feat: intercept incompatible signature replay

internal/runtime/executor/antigravity_executor.go

@@ -245,7 +245,9 @@ func validateAntigravityRequestSignatures(from sdktranslator.Format, rawJSON []b
 		return rawJSON, nil
 	}
 	// Always strip thinking blocks with invalid signatures (empty or non-Claude-format).
+	before := countClaudeThinkingBlocks(rawJSON)
 	rawJSON = antigravityclaude.StripEmptySignatureThinkingBlocks(rawJSON)
+	logAntigravitySignatureStrip(before, countClaudeThinkingBlocks(rawJSON), "prefix_cleanup", "empty_or_non_claude_signature")
 	if cache.SignatureCacheEnabled() {
 		return rawJSON, nil
 	}
@@ -254,12 +256,51 @@ func validateAntigravityRequestSignatures(from sdktranslator.Format, rawJSON []b
 		// by dropping unsigned thinking blocks silently (no 400).
 		return rawJSON, nil
 	}
-	if err := antigravityclaude.ValidateClaudeBypassSignatures(rawJSON); err != nil {
-		return rawJSON, statusErr{code: http.StatusBadRequest, msg: err.Error()}
-	}
+	before = countClaudeThinkingBlocks(rawJSON)
+	rawJSON = antigravityclaude.StripInvalidBypassSignatureThinkingBlocks(rawJSON)
+	logAntigravitySignatureStrip(before, countClaudeThinkingBlocks(rawJSON), "strict_bypass", "invalid_antigravity_claude_signature")
 	return rawJSON, nil
 }
 
+func countClaudeThinkingBlocks(rawJSON []byte) int {
+	messages := gjson.GetBytes(rawJSON, "messages")
+	if !messages.IsArray() {
+		return 0
+	}
+
+	count := 0
+	messages.ForEach(func(_, message gjson.Result) bool {
+		content := message.Get("content")
+		if !content.IsArray() {
+			return true
+		}
+		content.ForEach(func(_, part gjson.Result) bool {
+			if part.Get("type").String() == "thinking" {
+				count++
+			}
+			return true
+		})
+		return true
+	})
+	return count
+}
+
+func logAntigravitySignatureStrip(before, after int, stage, reason string) {
+	removed := before - after
+	if removed <= 0 {
+		return
+	}
+	log.WithFields(log.Fields{
+		"component":       "signature_sanitizer",
+		"executor":        "antigravity",
+		"target_provider": "claude",
+		"action":          "drop_thinking_blocks",
+		"stage":           stage,
+		"reason":          reason,
+		"count":           removed,
+	}).Debug("antigravity executor: dropped Claude thinking blocks with invalid signatures")
+}
+
 // Identifier returns the executor identifier.
 func (e *AntigravityExecutor) Identifier() string { return antigravityAuthType }
 

internal/runtime/executor/antigravity_executor_signature_test.go

@@ -4,16 +4,17 @@ import (
 	"bytes"
 	"context"
 	"encoding/base64"
-	"net/http"
-	"net/http/httptest"
-	"sync/atomic"
+	"fmt"
+	"strings"
 	"testing"
 	"time"
 
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/cache"
 	cliproxyauth "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/auth"
-	cliproxyexecutor "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/executor"
 	sdktranslator "github.com/router-for-me/CLIProxyAPI/v7/sdk/translator"
+	log "github.com/sirupsen/logrus"
+	"github.com/sirupsen/logrus/hooks/test"
+	"github.com/tidwall/gjson"
 )
 
 func testGeminiSignaturePayload() string {
@@ -56,7 +57,38 @@ func invalidClaudeThinkingPayload() []byte {
 	}`)
 }
 
-func TestAntigravityExecutor_StrictBypassRejectsInvalidSignature(t *testing.T) {
+func newSignatureDebugHook(t *testing.T) *test.Hook {
+	t.Helper()
+
+	previousLevel := log.GetLevel()
+	log.SetLevel(log.DebugLevel)
+	hook := test.NewLocal(log.StandardLogger())
+	t.Cleanup(func() {
+		hook.Reset()
+		log.SetLevel(previousLevel)
+	})
+	return hook
+}
+
+func assertSignatureDebugDoesNotLeak(t *testing.T, hook *test.Hook, forbidden string) {
+	t.Helper()
+
+	if forbidden == "" {
+		return
+	}
+	for _, entry := range hook.AllEntries() {
+		if strings.Contains(entry.Message, forbidden) {
+			t.Fatalf("debug log leaked signature in message: %q", entry.Message)
+		}
+		for key, value := range entry.Data {
+			if strings.Contains(fmt.Sprint(value), forbidden) {
+				t.Fatalf("debug log leaked signature in field %q: %v", key, value)
+			}
+		}
+	}
+}
+
+func TestAntigravityExecutor_StrictBypassStripsInvalidSignature(t *testing.T) {
 	previousCache := cache.SignatureCacheEnabled()
 	previousStrict := cache.SignatureBypassStrictMode()
 	cache.SetSignatureCacheEnabled(false)
@@ -66,67 +98,122 @@ func TestAntigravityExecutor_StrictBypassRejectsInvalidSignature(t *testing.T) {
 		cache.SetSignatureBypassStrictMode(previousStrict)
 	})
 
-	var hits atomic.Int32
-	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		hits.Add(1)
-		w.WriteHeader(http.StatusOK)
-		_, _ = w.Write([]byte(`{"response":{"candidates":[{"content":{"parts":[{"text":"ok"}]}}]}}`))
-	}))
-	defer server.Close()
-
-	executor := NewAntigravityExecutor(nil)
-	auth := testAntigravityAuth(server.URL)
 	payload := invalidClaudeThinkingPayload()
-	opts := cliproxyexecutor.Options{SourceFormat: sdktranslator.FromString("claude"), OriginalRequest: payload}
-	req := cliproxyexecutor.Request{Model: "claude-sonnet-4-5-thinking", Payload: payload}
+	from := sdktranslator.FromString("claude")
 
-	tests := []struct {
-		name   string
-		invoke func() error
-	}{
-		{
-			name: "execute",
-			invoke: func() error {
-				_, err := executor.Execute(context.Background(), auth, req, opts)
-				return err
-			},
-		},
-		{
-			name: "stream",
-			invoke: func() error {
-				_, err := executor.ExecuteStream(context.Background(), auth, req, cliproxyexecutor.Options{SourceFormat: opts.SourceFormat, OriginalRequest: payload, Stream: true})
-				return err
-			},
-		},
-		{
-			name: "count tokens",
-			invoke: func() error {
-				_, err := executor.CountTokens(context.Background(), auth, req, opts)
-				return err
-			},
-		},
+	output, err := validateAntigravityRequestSignatures(from, payload)
+	if err != nil {
+		t.Fatalf("strict bypass should strip invalid signatures instead of rejecting request: %v", err)
+	}
+	parts := gjson.GetBytes(output, "messages.0.content").Array()
+	if len(parts) != 1 {
+		t.Fatalf("content length = %d, want 1 after invalid thinking strip: %s", len(parts), output)
+	}
+	if got := parts[0].Get("type").String(); got != "text" {
+		t.Fatalf("remaining part type = %q, want text: %s", got, output)
+	}
+}
+
+func TestAntigravityExecutor_StrictBypassLogsStrippedInvalidSignature(t *testing.T) {
+	previousCache := cache.SignatureCacheEnabled()
+	previousStrict := cache.SignatureBypassStrictMode()
+	cache.SetSignatureCacheEnabled(false)
+	cache.SetSignatureBypassStrictMode(true)
+	t.Cleanup(func() {
+		cache.SetSignatureCacheEnabled(previousCache)
+		cache.SetSignatureBypassStrictMode(previousStrict)
+	})
+
+	hook := newSignatureDebugHook(t)
+	rawSignature := testFakeClaudeSignature()
+	payload := []byte(`{
+		"model": "claude-sonnet-4-5-thinking",
+		"messages": [
+			{
+				"role": "assistant",
+				"content": [
+					{"type": "thinking", "thinking": "bad", "signature": "` + rawSignature + `"},
+					{"type": "text", "text": "hello"}
+				]
+			}
+		]
+	}`)
+	from := sdktranslator.FromString("claude")
+
+	if _, err := validateAntigravityRequestSignatures(from, payload); err != nil {
+		t.Fatalf("strict bypass should strip invalid signatures instead of rejecting request: %v", err)
 	}
 
-	for _, tt := range tests {
-		tt := tt
-		t.Run(tt.name, func(t *testing.T) {
-			err := tt.invoke()
-			if err == nil {
-				t.Fatal("expected invalid signature to return an error")
+	found := false
+	for _, entry := range hook.AllEntries() {
+		if entry.Level != log.DebugLevel {
+			continue
+		}
+		if entry.Data["component"] != "signature_sanitizer" ||
+			entry.Data["executor"] != "antigravity" ||
+			entry.Data["action"] != "drop_thinking_blocks" ||
+			entry.Data["stage"] != "strict_bypass" {
+			continue
+		}
+		if entry.Data["count"] != 1 {
+			t.Fatalf("debug drop count = %v, want 1", entry.Data["count"])
+		}
+		found = true
+	}
+	if !found {
+		t.Fatal("expected debug log for stripped Antigravity Claude thinking signature")
+	}
+	assertSignatureDebugDoesNotLeak(t, hook, rawSignature)
+}
+
+func TestClaudeExecutor_LogsSanitizedClaudeUpstreamSignatures(t *testing.T) {
+	hook := newSignatureDebugHook(t)
+	rawSignature := "skip_thought_signature_validator"
+	body := []byte(`{
+		"model": "claude-sonnet-4-5",
+		"messages": [
+			{
+				"role": "assistant",
+				"content": [
+					{"type": "thinking", "thinking": "bad", "signature": "` + rawSignature + `"},
+					{"type": "text", "text": "hello"},
+					{"type": "tool_use", "id": "call_123", "name": "get_weather", "input": {}, "signature": "` + rawSignature + `"}
+				]
 			}
-			statusProvider, ok := err.(interface{ StatusCode() int })
-			if !ok {
-				t.Fatalf("expected status error, got %T: %v", err, err)
-			}
-			if statusProvider.StatusCode() != http.StatusBadRequest {
-				t.Fatalf("status = %d, want %d", statusProvider.StatusCode(), http.StatusBadRequest)
-			}
-		})
+		]
+	}`)
+
+	output := sanitizeClaudeMessagesForClaudeUpstreamWithDebug(context.Background(), body, "claude-sonnet-4-5")
+	parts := gjson.GetBytes(output, "messages.0.content").Array()
+	if len(parts) != 2 {
+		t.Fatalf("content length = %d, want 2 after invalid thinking strip: %s", len(parts), output)
+	}
+	if parts[1].Get("signature").Exists() {
+		t.Fatalf("tool_use signature should be removed before Claude upstream: %s", output)
 	}
 
-	if got := hits.Load(); got != 0 {
-		t.Fatalf("expected invalid signature to be rejected before upstream request, got %d upstream hits", got)
+	found := false
+	for _, entry := range hook.AllEntries() {
+		if entry.Level != log.DebugLevel {
+			continue
+		}
+		if entry.Data["component"] != "signature_sanitizer" ||
+			entry.Data["executor"] != "claude" ||
+			entry.Data["action"] != "sanitize_claude_messages" {
+			continue
+		}
+		if entry.Data["dropped_blocks"] != 1 {
+			t.Fatalf("dropped_blocks = %v, want 1", entry.Data["dropped_blocks"])
+		}
+		if entry.Data["dropped_signatures"] != 1 {
+			t.Fatalf("dropped_signatures = %v, want 1", entry.Data["dropped_signatures"])
+		}
+		found = true
 	}
+	if !found {
+		t.Fatal("expected debug log for Claude upstream signature sanitization")
+	}
+	assertSignatureDebugDoesNotLeak(t, hook, rawSignature)
 }
 
 func TestAntigravityExecutor_NonStrictBypassSkipsPrecheck(t *testing.T) {

internal/runtime/executor/claude_executor.go

@@ -22,6 +22,7 @@ import (
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/misc"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/registry"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/runtime/executor/helps"
+	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	cliproxyauth "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/auth"
@@ -44,6 +45,38 @@ type ClaudeExecutor struct {
 // Previously "proxy_" was used but this is a detectable fingerprint difference.
 const claudeToolPrefix = ""
 
+func sanitizeClaudeMessagesForClaudeUpstreamWithDebug(ctx context.Context, body []byte, baseModel string) []byte {
+	sanitized, report := sigcompat.SanitizeClaudeMessagesForClaudeUpstream(body, baseModel)
+	logClaudeSignatureSanitizeReport(ctx, baseModel, report)
+	return sanitized
+}
+
+func logClaudeSignatureSanitizeReport(ctx context.Context, baseModel string, report sigcompat.SignatureSanitizeReport) {
+	if report.DroppedBlocks == 0 && report.DroppedSignatures == 0 && report.ReplacedSignatures == 0 {
+		return
+	}
+
+	fields := log.Fields{
+		"component":           "signature_sanitizer",
+		"executor":            "claude",
+		"action":              "sanitize_claude_messages",
+		"target_provider":     string(report.TargetProvider),
+		"target_model":        baseModel,
+		"preserved":           report.Preserved,
+		"dropped_blocks":      report.DroppedBlocks,
+		"dropped_signatures":  report.DroppedSignatures,
+		"replaced_signatures": report.ReplacedSignatures,
+	}
+	if len(report.Decisions) > 0 {
+		decision := report.Decisions[0]
+		fields["first_block_kind"] = string(decision.BlockKind)
+		fields["first_detected_provider"] = string(decision.DetectedProvider)
+		fields["first_reason"] = decision.Reason
+	}
+
+	helps.LogWithRequestID(ctx).WithFields(fields).Debug("claude executor: sanitized signature history before upstream")
+}
+
 // oauthToolRenameMap maps OpenCode-style (lowercase) tool names to Claude Code-style
 // (TitleCase) names. Anthropic uses tool name fingerprinting to detect third-party
 // clients on OAuth traffic. Renaming to official names avoids extra-usage billing.
@@ -195,6 +228,7 @@ func (e *ClaudeExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, r
 	if oauthToken {
 		bodyForUpstream, oauthToolNamesReverseMap = prepareClaudeOAuthToolNamesForUpstream(bodyForUpstream, claudeToolPrefix, auth.ToolPrefixDisabled())
 	}
+	bodyForUpstream = sanitizeClaudeMessagesForClaudeUpstreamWithDebug(ctx, bodyForUpstream, baseModel)
 	// Enable cch signing by default for OAuth tokens (not just experimental flag).
 	// Claude Code always computes cch; missing or invalid cch is a detectable fingerprint.
 	if oauthToken || experimentalCCHSigningEnabled(e.cfg, auth) {
@@ -372,6 +406,7 @@ func (e *ClaudeExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.A
 	if oauthToken {
 		bodyForUpstream, oauthToolNamesReverseMap = prepareClaudeOAuthToolNamesForUpstream(bodyForUpstream, claudeToolPrefix, auth.ToolPrefixDisabled())
 	}
+	bodyForUpstream = sanitizeClaudeMessagesForClaudeUpstreamWithDebug(ctx, bodyForUpstream, baseModel)
 	// Enable cch signing by default for OAuth tokens (not just experimental flag).
 	if oauthToken || experimentalCCHSigningEnabled(e.cfg, auth) {
 		bodyForUpstream = signAnthropicMessagesBody(bodyForUpstream)
@@ -613,6 +648,7 @@ func (e *ClaudeExecutor) CountTokens(ctx context.Context, auth *cliproxyauth.Aut
 	if isClaudeOAuthToken(apiKey) {
 		body, _ = prepareClaudeOAuthToolNamesForUpstream(body, claudeToolPrefix, auth.ToolPrefixDisabled())
 	}
+	body = sanitizeClaudeMessagesForClaudeUpstreamWithDebug(ctx, body, baseModel)
 
 	url := fmt.Sprintf("%s/v1/messages/count_tokens?beta=true", baseURL)
 	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(body))

internal/runtime/executor/claude_executor_test.go

@@ -1251,6 +1251,63 @@ func TestClaudeExecutor_CountTokens_AppliesCacheControlGuards(t *testing.T) {
 	}
 }
 
+func TestClaudeExecutor_ExecuteSanitizesSignaturesBeforeUpstream(t *testing.T) {
+	var seenBody []byte
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, _ := io.ReadAll(r.Body)
+		seenBody = bytes.Clone(body)
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"id":"msg_1","type":"message","model":"claude-sonnet-4-5","role":"assistant","content":[{"type":"text","text":"ok"}],"usage":{"input_tokens":1,"output_tokens":1}}`))
+	}))
+	defer server.Close()
+
+	executor := NewClaudeExecutor(&config.Config{})
+	auth := &cliproxyauth.Auth{Attributes: map[string]string{
+		"api_key":  "key-123",
+		"base_url": server.URL,
+	}}
+
+	payload := []byte(`{
+		"model": "claude-sonnet-4-5",
+		"max_tokens": 16,
+		"messages": [
+			{"role":"assistant","content":[
+				{"type":"thinking","thinking":"drop this","signature":""},
+				{"type":"text","text":"I will run git status."},
+				{"type":"tool_use","id":"Bash-1","name":"Bash","input":{"command":"git status"},"signature":"bad","thoughtSignature":"bad2","model":"claude-opus-4-1"}
+			]},
+			{"role":"user","content":[{"type":"tool_result","tool_use_id":"Bash-1","content":"ok"}]}
+		]
+	}`)
+
+	if _, err := executor.Execute(context.Background(), auth, cliproxyexecutor.Request{
+		Model:   "claude-sonnet-4-5",
+		Payload: payload,
+	}, cliproxyexecutor.Options{
+		SourceFormat: sdktranslator.FromString("claude"),
+		Stream:       false,
+	}); err != nil {
+		t.Fatalf("Execute error: %v", err)
+	}
+
+	parts := gjson.GetBytes(seenBody, "messages.0.content").Array()
+	if len(parts) != 2 {
+		t.Fatalf("messages.0.content length = %d, want 2; body=%s", len(parts), seenBody)
+	}
+	if parts[0].Get("type").String() != "text" {
+		t.Fatalf("first remaining part = %s, want text", parts[0].Raw)
+	}
+	toolUse := parts[1]
+	if toolUse.Get("type").String() != "tool_use" {
+		t.Fatalf("second remaining part = %s, want tool_use", toolUse.Raw)
+	}
+	for _, path := range []string{"signature", "thoughtSignature", "model"} {
+		if toolUse.Get(path).Exists() {
+			t.Fatalf("tool_use.%s should be removed before upstream: %s", path, seenBody)
+		}
+	}
+}
+
 func hasTTLOrderingViolation(payload []byte) bool {
 	seen5m := false
 	violates := false

internal/runtime/executor/codex_executor.go

@@ -285,6 +285,7 @@ func (e *CodexExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, re
 	if e.cfg == nil || e.cfg.DisableImageGeneration == config.DisableImageGenerationOff {
 		body = ensureImageGenerationTool(body, baseModel, auth)
 	}
+	body = sanitizeOpenAIResponsesReasoningEncryptedContent(ctx, "codex executor", body)
 	reporter.SetTranslatedReasoningEffort(body, to.String())
 
 	url := strings.TrimSuffix(baseURL, "/") + "/responses"
@@ -443,6 +444,7 @@ func (e *CodexExecutor) executeCompact(ctx context.Context, auth *cliproxyauth.A
 	if e.cfg == nil || e.cfg.DisableImageGeneration == config.DisableImageGenerationOff {
 		body = ensureImageGenerationTool(body, baseModel, auth)
 	}
+	body = sanitizeOpenAIResponsesReasoningEncryptedContent(ctx, "codex executor", body)
 	reporter.SetTranslatedReasoningEffort(body, to.String())
 
 	url := strings.TrimSuffix(baseURL, "/") + "/responses/compact"
@@ -546,6 +548,7 @@ func (e *CodexExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.Au
 	if e.cfg == nil || e.cfg.DisableImageGeneration == config.DisableImageGenerationOff {
 		body = ensureImageGenerationTool(body, baseModel, auth)
 	}
+	body = sanitizeOpenAIResponsesReasoningEncryptedContent(ctx, "codex executor", body)
 	reporter.SetTranslatedReasoningEffort(body, to.String())
 
 	url := strings.TrimSuffix(baseURL, "/") + "/responses"

internal/runtime/executor/codex_executor_signature_test.go

@@ -0,0 +1,138 @@
+package executor
+
+import (
+	"context"
+	"encoding/base64"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/config"
+	cliproxyauth "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/auth"
+	cliproxyexecutor "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/executor"
+	sdktranslator "github.com/router-for-me/CLIProxyAPI/v7/sdk/translator"
+	"github.com/tidwall/gjson"
+)
+
+func validCodexReasoningEncryptedContentForTest() string {
+	payload := make([]byte, 1+8+16+16+32)
+	payload[0] = 0x80
+	for i := 9; i < len(payload); i++ {
+		payload[i] = byte(i)
+	}
+	return base64.RawURLEncoding.EncodeToString(payload)
+}
+
+func newCodexSignatureTestAuth(serverURL string) *cliproxyauth.Auth {
+	return &cliproxyauth.Auth{Attributes: map[string]string{
+		"base_url": serverURL,
+		"api_key":  "test",
+	}}
+}
+
+func TestCodexExecutorDropsInvalidReasoningEncryptedContentFromFinalRequest(t *testing.T) {
+	validEncryptedContent := validCodexReasoningEncryptedContentForTest()
+	var gotBody []byte
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, errRead := io.ReadAll(r.Body)
+		if errRead != nil {
+			t.Fatalf("read body: %v", errRead)
+		}
+		gotBody = body
+		w.Header().Set("Content-Type", "text/event-stream")
+		_, _ = w.Write([]byte("data: {\"type\":\"response.completed\",\"response\":{\"id\":\"resp_1\",\"object\":\"response\",\"created_at\":0,\"status\":\"completed\",\"background\":false,\"error\":null}}\n\n"))
+	}))
+	defer server.Close()
+
+	executor := NewCodexExecutor(&config.Config{})
+	_, err := executor.Execute(context.Background(), newCodexSignatureTestAuth(server.URL), cliproxyexecutor.Request{
+		Model: "gpt-5.4",
+		Payload: []byte(`{"model":"gpt-5.4","input":[` +
+			`{"id":"rs_bad","type":"reasoning","encrypted_content":"gAAAAABqFTIa\u2026abc","summary":[]},` +
+			`{"id":"rs_non_string","type":"reasoning","encrypted_content":123,"summary":[]},` +
+			`{"id":"rs_good","type":"reasoning","encrypted_content":"` + validEncryptedContent + `","summary":[]},` +
+			`{"role":"user","content":"hello","encrypted_content":"leave-message-alone"}` +
+			`]}`),
+	}, cliproxyexecutor.Options{
+		SourceFormat: sdktranslator.FromString("openai-response"),
+		Stream:       false,
+	})
+	if err != nil {
+		t.Fatalf("Execute error: %v", err)
+	}
+
+	if gjson.GetBytes(gotBody, "input.0.encrypted_content").Exists() {
+		t.Fatalf("invalid reasoning encrypted_content exists, want removed; body=%s", string(gotBody))
+	}
+	if gjson.GetBytes(gotBody, "input.1.encrypted_content").Exists() {
+		t.Fatalf("non-string reasoning encrypted_content exists, want removed; body=%s", string(gotBody))
+	}
+	if got := gjson.GetBytes(gotBody, "input.2.encrypted_content").String(); got != validEncryptedContent {
+		t.Fatalf("valid reasoning encrypted_content = %q, want preserved", got)
+	}
+	if got := gjson.GetBytes(gotBody, "input.3.encrypted_content").String(); got != "leave-message-alone" {
+		t.Fatalf("non-reasoning encrypted_content = %q, want untouched", got)
+	}
+}
+
+func TestCodexExecutorExecuteStreamDropsInvalidReasoningEncryptedContentFromFinalRequest(t *testing.T) {
+	var gotBody []byte
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, errRead := io.ReadAll(r.Body)
+		if errRead != nil {
+			t.Fatalf("read body: %v", errRead)
+		}
+		gotBody = body
+		w.Header().Set("Content-Type", "text/event-stream")
+		_, _ = w.Write([]byte("data: {\"type\":\"response.completed\",\"response\":{\"id\":\"resp_1\",\"object\":\"response\",\"created_at\":0,\"status\":\"completed\",\"background\":false,\"error\":null}}\n\n"))
+	}))
+	defer server.Close()
+
+	executor := NewCodexExecutor(&config.Config{})
+	result, err := executor.ExecuteStream(context.Background(), newCodexSignatureTestAuth(server.URL), cliproxyexecutor.Request{
+		Model:   "gpt-5.4",
+		Payload: []byte(`{"model":"gpt-5.4","stream":true,"input":[{"id":"rs_bad","type":"reasoning","encrypted_content":"bad","summary":[]}]}`),
+	}, cliproxyexecutor.Options{
+		SourceFormat: sdktranslator.FromString("openai-response"),
+		Stream:       true,
+	})
+	if err != nil {
+		t.Fatalf("ExecuteStream error: %v", err)
+	}
+	for range result.Chunks {
+	}
+	if gjson.GetBytes(gotBody, "input.0.encrypted_content").Exists() {
+		t.Fatalf("invalid stream reasoning encrypted_content exists, want removed; body=%s", string(gotBody))
+	}
+}
+
+func TestCodexExecutorCompactDropsInvalidReasoningEncryptedContentFromFinalRequest(t *testing.T) {
+	var gotBody []byte
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, errRead := io.ReadAll(r.Body)
+		if errRead != nil {
+			t.Fatalf("read body: %v", errRead)
+		}
+		gotBody = body
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"id":"resp_1","object":"response.compaction","usage":{"input_tokens":1,"output_tokens":2,"total_tokens":3}}`))
+	}))
+	defer server.Close()
+
+	executor := NewCodexExecutor(&config.Config{})
+	_, err := executor.Execute(context.Background(), newCodexSignatureTestAuth(server.URL), cliproxyexecutor.Request{
+		Model:   "gpt-5.4",
+		Payload: []byte(`{"model":"gpt-5.4","input":[{"id":"rs_bad","type":"reasoning","encrypted_content":"bad","summary":[]}]}`),
+	}, cliproxyexecutor.Options{
+		SourceFormat: sdktranslator.FromString("openai-response"),
+		Alt:          "responses/compact",
+		Stream:       false,
+	})
+	if err != nil {
+		t.Fatalf("Execute compact error: %v", err)
+	}
+	if gjson.GetBytes(gotBody, "input.0.encrypted_content").Exists() {
+		t.Fatalf("invalid compact reasoning encrypted_content exists, want removed; body=%s", string(gotBody))
+	}
+}

internal/runtime/executor/codex_websockets_executor.go

@@ -213,6 +213,7 @@ func (e *CodexWebsocketsExecutor) Execute(ctx context.Context, auth *cliproxyaut
 	if e.cfg == nil || e.cfg.DisableImageGeneration == config.DisableImageGenerationOff {
 		body = ensureImageGenerationTool(body, baseModel, auth)
 	}
+	body = sanitizeOpenAIResponsesReasoningEncryptedContent(ctx, "codex websockets executor", body)
 
 	httpURL := strings.TrimSuffix(baseURL, "/") + "/responses"
 	wsURL, err := buildCodexResponsesWebsocketURL(httpURL)
@@ -417,6 +418,7 @@ func (e *CodexWebsocketsExecutor) ExecuteStream(ctx context.Context, auth *clipr
 	if e.cfg == nil || e.cfg.DisableImageGeneration == config.DisableImageGenerationOff {
 		body = ensureImageGenerationTool(body, baseModel, auth)
 	}
+	body = sanitizeOpenAIResponsesReasoningEncryptedContent(ctx, "codex websockets executor", body)
 
 	httpURL := strings.TrimSuffix(baseURL, "/") + "/responses"
 	wsURL, err := buildCodexResponsesWebsocketURL(httpURL)

internal/runtime/executor/openai_compat_executor.go

@@ -125,6 +125,7 @@ func (e *OpenAICompatExecutor) Execute(ctx context.Context, auth *cliproxyauth.A
 		if updated, errDelete := sjson.DeleteBytes(translated, "stream"); errDelete == nil {
 			translated = updated
 		}
+		translated = sanitizeOpenAIResponsesReasoningEncryptedContent(ctx, "openai compat executor", translated)
 	}
 	reporter.SetTranslatedReasoningEffort(translated, to.String())
 

internal/runtime/executor/openai_responses_signature.go

@@ -0,0 +1,68 @@
+package executor
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/runtime/executor/helps"
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
+	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
+)
+
+func sanitizeOpenAIResponsesReasoningEncryptedContent(ctx context.Context, provider string, body []byte) []byte {
+	input := gjson.GetBytes(body, "input")
+	if !input.Exists() || !input.IsArray() {
+		return body
+	}
+	provider = strings.TrimSpace(provider)
+	if provider == "" {
+		provider = "openai responses upstream"
+	}
+
+	updated := body
+	for index, item := range input.Array() {
+		if strings.TrimSpace(item.Get("type").String()) != "reasoning" {
+			continue
+		}
+
+		encryptedContentPath := fmt.Sprintf("input.%d.encrypted_content", index)
+		encryptedContent := gjson.GetBytes(updated, encryptedContentPath)
+		if !encryptedContent.Exists() {
+			continue
+		}
+
+		reason := ""
+		switch encryptedContent.Type {
+		case gjson.String:
+			rawSignature := encryptedContent.String()
+			if rawSignature != strings.TrimSpace(rawSignature) {
+				reason = "encrypted_content has leading or trailing whitespace"
+			} else if _, err := signature.InspectGPTReasoningSignature(rawSignature); err != nil {
+				reason = err.Error()
+			}
+		case gjson.Null:
+			reason = "encrypted_content is null"
+		default:
+			reason = fmt.Sprintf("encrypted_content must be a string, got %s", encryptedContent.Type.String())
+		}
+		if reason == "" {
+			continue
+		}
+
+		next, err := sjson.DeleteBytes(updated, encryptedContentPath)
+		if err != nil {
+			helps.LogWithRequestID(ctx).Debugf("%s: failed to drop invalid reasoning encrypted_content at input[%d]: %v", provider, index, err)
+			continue
+		}
+		updated = next
+
+		itemID := strings.TrimSpace(gjson.GetBytes(updated, fmt.Sprintf("input.%d.id", index)).String())
+		if itemID == "" {
+			itemID = fmt.Sprintf("input[%d]", index)
+		}
+		helps.LogWithRequestID(ctx).Debugf("%s: dropped invalid reasoning encrypted_content at input[%d] item_id=%q reason=%s", provider, index, itemID, reason)
+	}
+	return updated
+}

internal/signature/claude_messages_sanitize.go

@@ -9,10 +9,11 @@ import (
 )
 
 type ClaudeMessagesSignatureSanitizeOptions struct {
-	TargetProvider     SignatureProvider
-	TargetModel        string
-	DropEmptyMessages  bool
-	DropToolSignatures bool
+	TargetProvider                SignatureProvider
+	TargetModel                   string
+	DropEmptyMessages             bool
+	DropToolSignatures            bool
+	DropEmptyThinkingPlaceholders bool
 }
 
 type SignatureSanitizeReport struct {
@@ -35,6 +36,20 @@ func SanitizeClaudeMessagesSignaturesForModel(payload []byte, targetModel string
 	})
 }
 
+// SanitizeClaudeMessagesForClaudeUpstream prepares a Claude /v1/messages body
+// for native Claude upstreams. Invalid thinking blocks are dropped, valid
+// thinking signatures are normalized to Claude provider-native E-form, and
+// tool_use blocks keep only their tool-call payload.
+func SanitizeClaudeMessagesForClaudeUpstream(payload []byte, targetModel string) ([]byte, SignatureSanitizeReport) {
+	return SanitizeClaudeMessagesSignaturesForTarget(payload, ClaudeMessagesSignatureSanitizeOptions{
+		TargetProvider:                SignatureProviderClaude,
+		TargetModel:                   targetModel,
+		DropEmptyMessages:             true,
+		DropToolSignatures:            true,
+		DropEmptyThinkingPlaceholders: true,
+	})
+}
+
 // SanitizeClaudeMessagesSignaturesForTarget applies provider-aware signature
 // compatibility rules to Claude /v1/messages history. Compatible thinking
 // signatures are preserved. Incompatible thinking blocks are removed so a user
@@ -103,7 +118,7 @@ func SanitizeClaudeMessagesSignaturesForTarget(payload []byte, opts ClaudeMessag
 				continue
 			}
 
-			if targetProvider == SignatureProviderClaude && isEmptyClaudeThinkingPlaceholder(part) {
+			if targetProvider == SignatureProviderClaude && isEmptyClaudeThinkingPlaceholder(part) && !opts.DropEmptyThinkingPlaceholders {
 				keptParts = append(keptParts, part.Raw)
 				continue
 			}
@@ -162,7 +177,7 @@ func SanitizeClaudeMessagesSignaturesForTarget(payload []byte, opts ClaudeMessag
 func stripClaudeToolUseSignatureFields(part gjson.Result) (string, bool) {
 	updated := part.Raw
 	changed := false
-	for _, sigPath := range claudeToolUseSignaturePaths() {
+	for _, sigPath := range claudeToolUseProvenancePaths() {
 		if !gjson.Get(updated, sigPath).Exists() {
 			continue
 		}
@@ -231,11 +246,16 @@ func sanitizeClaudeToolUseSignature(part gjson.Result, targetProvider SignatureP
 func claudeToolUseSignaturePaths() []string {
 	return []string{
 		"signature",
+		"thoughtSignature",
 		"thought_signature",
 		"extra_content.google.thought_signature",
 	}
 }
 
+func claudeToolUseProvenancePaths() []string {
+	return append(claudeToolUseSignaturePaths(), "model")
+}
+
 func deleteEmptyJSONObjectPath(raw, path string) (string, bool) {
 	result := gjson.Get(raw, path)
 	if !result.Exists() || !result.IsObject() || len(result.Map()) != 0 {

internal/signature/gemini_sanitize.go

@@ -0,0 +1,140 @@
+package signature
+
+import (
+	"fmt"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
+)
+
+// GeminiReplaySignatureOrBypass returns a Gemini-replayable thoughtSignature.
+// Compatible Gemini signatures are normalized and preserved. Missing, unknown,
+// or cross-provider signatures are replaced with Gemini's bypass sentinel.
+func GeminiReplaySignatureOrBypass(rawSignature string, blockKind SignatureBlockKind) string {
+	if signature, ok := CompatibleSignatureForProviderBlock(SignatureProviderGemini, rawSignature, blockKind); ok {
+		return signature
+	}
+	decision := DecideSignatureCompatibility(SignatureProviderGemini, rawSignature, blockKind)
+	if decision.Action == SignatureActionReplaceWithGeminiBypass && decision.ReplacementSignature != "" {
+		return decision.ReplacementSignature
+	}
+	return GeminiSkipThoughtSignatureValidator
+}
+
+// SanitizeGeminiRequestThoughtSignatures applies Gemini replay policy to a
+// Gemini-shaped request. Model-turn functionCall, thought, and signed parts keep
+// compatible Gemini signatures and use the bypass sentinel otherwise. User-turn
+// functionResponse parts must not carry thoughtSignature fields.
+func SanitizeGeminiRequestThoughtSignatures(payload []byte, contentsPath string) []byte {
+	contentsPath = strings.TrimSpace(contentsPath)
+	if contentsPath == "" {
+		contentsPath = "contents"
+	}
+
+	contents := gjson.GetBytes(payload, contentsPath)
+	if !contents.IsArray() {
+		return payload
+	}
+
+	contents.ForEach(func(contentIdx, content gjson.Result) bool {
+		isModelTurn := content.Get("role").String() == "model"
+		parts := content.Get("parts")
+		if !parts.IsArray() {
+			return true
+		}
+
+		parts.ForEach(func(partIdx, part gjson.Result) bool {
+			partPath := fmt.Sprintf("%s.%d.parts.%d", contentsPath, contentIdx.Int(), partIdx.Int())
+			if part.Get("functionResponse").Exists() {
+				_, hadSignature := geminiPartThoughtSignature(part)
+				payload = deleteGeminiPartThoughtSignatureFields(payload, partPath)
+				if hadSignature {
+					logGeminiThoughtSignatureSanitize(contentsPath, int(contentIdx.Int()), int(partIdx.Int()), SignatureCompatibilityDecision{
+						TargetProvider: SignatureProviderGemini,
+						BlockKind:      SignatureBlockKindGeminiModelPart,
+						Action:         SignatureActionDropSignature,
+						Reason:         "user-turn functionResponse parts cannot replay thought signatures",
+					}, "", true)
+				}
+				return true
+			}
+			if !isModelTurn {
+				return true
+			}
+
+			hasFunctionCall := part.Get("functionCall").Exists()
+			hasThought := part.Get("thought").Exists()
+			rawSignature, hasSignature := geminiPartThoughtSignature(part)
+			if !hasFunctionCall && !hasThought && !hasSignature {
+				return true
+			}
+
+			blockKind := SignatureBlockKindGeminiModelPart
+			if hasFunctionCall {
+				blockKind = SignatureBlockKindGeminiFunctionCall
+			}
+			payload = deleteGeminiPartThoughtSignatureFields(payload, partPath)
+			decision := DecideSignatureCompatibility(SignatureProviderGemini, rawSignature, blockKind)
+			replaySignature := GeminiReplaySignatureOrBypass(rawSignature, blockKind)
+			payload, _ = sjson.SetBytes(payload, partPath+".thoughtSignature", replaySignature)
+			if decision.Action != SignatureActionPreserve {
+				logGeminiThoughtSignatureSanitize(contentsPath, int(contentIdx.Int()), int(partIdx.Int()), decision, rawSignature, hasSignature)
+			}
+			return true
+		})
+		return true
+	})
+
+	return payload
+}
+
+func logGeminiThoughtSignatureSanitize(contentsPath string, contentIndex, partIndex int, decision SignatureCompatibilityDecision, rawSignature string, hasSignature bool) {
+	log.WithFields(log.Fields{
+		"component":         "signature_sanitizer",
+		"target_provider":   string(SignatureProviderGemini),
+		"action":            string(decision.Action),
+		"reason":            decision.Reason,
+		"contents_path":     contentsPath,
+		"content_index":     contentIndex,
+		"part_index":        partIndex,
+		"block_kind":        string(decision.BlockKind),
+		"detected_provider": string(decision.DetectedProvider),
+		"has_signature":     hasSignature,
+		"signature_length":  len(strings.TrimSpace(rawSignature)),
+	}).Debug("gemini request: sanitized thoughtSignature before upstream")
+}
+
+func geminiPartThoughtSignature(part gjson.Result) (string, bool) {
+	for _, path := range []string{
+		"thoughtSignature",
+		"thought_signature",
+		"functionCall.thoughtSignature",
+		"functionCall.thought_signature",
+		"functionResponse.thoughtSignature",
+		"functionResponse.thought_signature",
+		"extra_content.google.thought_signature",
+	} {
+		result := part.Get(path)
+		if result.Exists() {
+			return result.String(), true
+		}
+	}
+	return "", false
+}
+
+func deleteGeminiPartThoughtSignatureFields(payload []byte, partPath string) []byte {
+	for _, path := range []string{
+		"thoughtSignature",
+		"thought_signature",
+		"functionCall.thoughtSignature",
+		"functionCall.thought_signature",
+		"functionResponse.thoughtSignature",
+		"functionResponse.thought_signature",
+		"extra_content.google.thought_signature",
+	} {
+		payload, _ = sjson.DeleteBytes(payload, partPath+"."+path)
+	}
+	return payload
+}

internal/signature/gemini_sanitize_test.go

@@ -0,0 +1,122 @@
+package signature
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/sirupsen/logrus/hooks/test"
+	"github.com/tidwall/gjson"
+)
+
+func newSignatureDebugHook(t *testing.T) *test.Hook {
+	t.Helper()
+
+	previousLevel := log.GetLevel()
+	log.SetLevel(log.DebugLevel)
+	hook := test.NewLocal(log.StandardLogger())
+	t.Cleanup(func() {
+		hook.Reset()
+		log.SetLevel(previousLevel)
+	})
+	return hook
+}
+
+func assertSignatureDebugDoesNotLeak(t *testing.T, hook *test.Hook, forbidden string) {
+	t.Helper()
+
+	if forbidden == "" {
+		return
+	}
+	for _, entry := range hook.AllEntries() {
+		if strings.Contains(entry.Message, forbidden) {
+			t.Fatalf("debug log leaked signature in message: %q", entry.Message)
+		}
+		for key, value := range entry.Data {
+			if strings.Contains(fmt.Sprint(value), forbidden) {
+				t.Fatalf("debug log leaked signature in field %q: %v", key, value)
+			}
+		}
+	}
+}
+
+func TestSanitizeGeminiRequestThoughtSignaturesPreservesGeminiSignature(t *testing.T) {
+	sig := testGemini3ThoughtSignature([]byte{0x01, 0x0c, 0x39})
+	input := []byte(`{"contents":[{"role":"model","parts":[{"functionCall":{"name":"f","args":{}},"thoughtSignature":"` + sig + `"}]}]}`)
+
+	out := SanitizeGeminiRequestThoughtSignatures(input, "contents")
+
+	if got := gjson.GetBytes(out, "contents.0.parts.0.thoughtSignature").String(); got != sig {
+		t.Fatalf("thoughtSignature = %q, want %q. Output: %s", got, sig, string(out))
+	}
+}
+
+func TestSanitizeGeminiRequestThoughtSignaturesReplacesBase64UUIDFunctionCall(t *testing.T) {
+	sig := testGeminiThoughtSignature([]byte("e24830a7-5cd6-42fe-998b-ee539e72b9c3"))
+	input := []byte(`{"contents":[{"role":"model","parts":[{"functionCall":{"name":"f","args":{},"thoughtSignature":"` + sig + `"}}]}]}`)
+
+	out := SanitizeGeminiRequestThoughtSignatures(input, "contents")
+
+	if got := gjson.GetBytes(out, "contents.0.parts.0.thoughtSignature").String(); got != GeminiSkipThoughtSignatureValidator {
+		t.Fatalf("thoughtSignature = %q, want bypass sentinel. Output: %s", got, string(out))
+	}
+	if gjson.GetBytes(out, "contents.0.parts.0.functionCall.thoughtSignature").Exists() {
+		t.Fatalf("nested functionCall thoughtSignature should be removed. Output: %s", string(out))
+	}
+}
+
+func TestSanitizeGeminiRequestThoughtSignaturesLogsBypassReplacement(t *testing.T) {
+	hook := newSignatureDebugHook(t)
+	sig := testGeminiThoughtSignature([]byte("e24830a7-5cd6-42fe-998b-ee539e72b9c3"))
+	input := []byte(`{"contents":[{"role":"model","parts":[{"functionCall":{"name":"f","args":{},"thoughtSignature":"` + sig + `"}}]}]}`)
+
+	out := SanitizeGeminiRequestThoughtSignatures(input, "contents")
+	if got := gjson.GetBytes(out, "contents.0.parts.0.thoughtSignature").String(); got != GeminiSkipThoughtSignatureValidator {
+		t.Fatalf("thoughtSignature = %q, want bypass sentinel. Output: %s", got, string(out))
+	}
+
+	found := false
+	for _, entry := range hook.AllEntries() {
+		if entry.Level != log.DebugLevel {
+			continue
+		}
+		if entry.Data["component"] != "signature_sanitizer" ||
+			entry.Data["target_provider"] != string(SignatureProviderGemini) ||
+			entry.Data["action"] != "replace_with_gemini_bypass" {
+			continue
+		}
+		if entry.Data["block_kind"] != string(SignatureBlockKindGeminiFunctionCall) {
+			t.Fatalf("block_kind = %v, want %s", entry.Data["block_kind"], SignatureBlockKindGeminiFunctionCall)
+		}
+		found = true
+	}
+	if !found {
+		t.Fatal("expected debug log for Gemini thoughtSignature bypass replacement")
+	}
+	assertSignatureDebugDoesNotLeak(t, hook, sig)
+}
+
+func TestSanitizeGeminiRequestThoughtSignaturesReplacesField2WrappedUUIDFunctionCall(t *testing.T) {
+	sig := testGemini3ThoughtSignature([]byte("e24830a7-5cd6-42fe-998b-ee539e72b9c3"))
+	input := []byte(`{"request":{"contents":[{"role":"model","parts":[{"functionCall":{"name":"f","args":{}},"thoughtSignature":"` + sig + `"}]}]}}`)
+
+	out := SanitizeGeminiRequestThoughtSignatures(input, "request.contents")
+
+	if got := gjson.GetBytes(out, "request.contents.0.parts.0.thoughtSignature").String(); got != GeminiSkipThoughtSignatureValidator {
+		t.Fatalf("thoughtSignature = %q, want bypass sentinel. Output: %s", got, string(out))
+	}
+}
+
+func TestSanitizeGeminiRequestThoughtSignaturesRemovesFunctionResponseSignature(t *testing.T) {
+	input := []byte(`{"contents":[{"role":"user","parts":[{"functionResponse":{"name":"f","response":{"result":"ok"},"thoughtSignature":"bad"},"thoughtSignature":"bad"}]}]}`)
+
+	out := SanitizeGeminiRequestThoughtSignatures(input, "contents")
+
+	if gjson.GetBytes(out, "contents.0.parts.0.thoughtSignature").Exists() {
+		t.Fatalf("functionResponse top-level thoughtSignature should be removed. Output: %s", string(out))
+	}
+	if gjson.GetBytes(out, "contents.0.parts.0.functionResponse.thoughtSignature").Exists() {
+		t.Fatalf("functionResponse nested thoughtSignature should be removed. Output: %s", string(out))
+	}
+}

internal/signature/provider_compatibility_test.go

@@ -282,3 +282,58 @@ func TestSanitizeClaudeMessagesSignaturesForModel_DropsEmptyAssistantMessage(t *
 		t.Fatalf("remaining role = %q, want user", got)
 	}
 }
+
+func TestSanitizeClaudeMessagesForClaudeUpstream_DropsInvalidThinkingAndCleansToolUse(t *testing.T) {
+	input := []byte(`{"messages":[{"role":"assistant","content":[{"type":"thinking","thinking":"drop me","signature":""},{"type":"text","text":"answer"},{"type":"tool_use","id":"toolu_1","name":"Bash","input":{"command":"git status"},"signature":"bad","thoughtSignature":"bad2","thought_signature":"bad3","model":"claude-sonnet-4-5","extra_content":{"google":{"thought_signature":"bad4"}}}]}]}`)
+
+	output, report := SanitizeClaudeMessagesForClaudeUpstream(input, "claude-sonnet-4-5")
+	if report.DroppedBlocks != 1 {
+		t.Fatalf("DroppedBlocks = %d, want 1; report=%+v", report.DroppedBlocks, report)
+	}
+	parts := gjson.GetBytes(output, "messages.0.content").Array()
+	if len(parts) != 2 {
+		t.Fatalf("content length = %d, want 2: %s", len(parts), output)
+	}
+	if parts[0].Get("type").String() != "text" {
+		t.Fatalf("first remaining part = %s, want text", parts[0].Raw)
+	}
+	toolUse := parts[1]
+	if toolUse.Get("type").String() != "tool_use" {
+		t.Fatalf("second remaining part = %s, want tool_use", toolUse.Raw)
+	}
+	if got := toolUse.Get("id").String(); got != "toolu_1" {
+		t.Fatalf("tool_use id = %q, want toolu_1", got)
+	}
+	for _, path := range []string{
+		"signature",
+		"thoughtSignature",
+		"thought_signature",
+		"model",
+		"extra_content",
+	} {
+		if toolUse.Get(path).Exists() {
+			t.Fatalf("tool_use.%s should be removed: %s", path, toolUse.Raw)
+		}
+	}
+}
+
+func TestSanitizeClaudeMessagesForClaudeUpstream_NormalizesValidThinkingAndDropsEmptyMessage(t *testing.T) {
+	nativeSig := testClaudeThinkingSignature()
+	doubleEncoded := base64.StdEncoding.EncodeToString([]byte(nativeSig))
+	input := []byte(`{"messages":[{"role":"assistant","content":[{"type":"thinking","thinking":"keep","signature":"` + doubleEncoded + `"},{"type":"text","text":"answer"}]},{"role":"assistant","content":[{"type":"thinking","thinking":"drop"}]},{"role":"user","content":[{"type":"text","text":"next"}]}]}`)
+
+	output, report := SanitizeClaudeMessagesForClaudeUpstream(input, "claude-sonnet-4-5")
+	if report.Preserved != 1 || report.DroppedBlocks != 1 {
+		t.Fatalf("unexpected report: %+v", report)
+	}
+	messages := gjson.GetBytes(output, "messages").Array()
+	if len(messages) != 2 {
+		t.Fatalf("messages length = %d, want 2: %s", len(messages), output)
+	}
+	if got := messages[0].Get("content.0.signature").String(); got != nativeSig {
+		t.Fatalf("signature = %q, want provider-native %q", got, nativeSig)
+	}
+	if got := messages[1].Get("role").String(); got != "user" {
+		t.Fatalf("remaining second role = %q, want user", got)
+	}
+}

internal/translator/antigravity/claude/antigravity_claude_request.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/cache"
+	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/translator/gemini/common"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
@@ -18,15 +19,30 @@ import (
 )
 
 func resolveThinkingSignature(modelName, thinkingText, rawSignature string) string {
+	targetProvider := sigcompat.SignatureProviderFromModelName(modelName)
+	if targetProvider == sigcompat.SignatureProviderGemini {
+		return resolveProviderCompatibleSignature(targetProvider, rawSignature, sigcompat.SignatureBlockKindGeminiModelPart)
+	}
 	if cache.SignatureCacheEnabled() {
 		return resolveCacheModeSignature(modelName, thinkingText, rawSignature)
 	}
-	return resolveBypassModeSignature(rawSignature)
+	if signature := resolveProviderCompatibleSignature(targetProvider, rawSignature, sigcompat.SignatureBlockKindUnknown); signature != "" {
+		return signature
+	}
+	return resolveBypassModeSignatureForProvider(targetProvider, rawSignature)
 }
 
 func resolveCacheModeSignature(modelName, thinkingText, rawSignature string) string {
+	targetProvider := sigcompat.SignatureProviderFromModelName(modelName)
 	if thinkingText != "" {
 		if cachedSig := cache.GetCachedSignature(modelName, thinkingText); cachedSig != "" {
+			if targetProvider == sigcompat.SignatureProviderClaude {
+				signature, ok := sigcompat.CompatibleAntigravityClaudeThinkingSignature(cachedSig)
+				if !ok {
+					return ""
+				}
+				return signature
+			}
 			return cachedSig
 		}
 	}
@@ -43,6 +59,13 @@ func resolveCacheModeSignature(modelName, thinkingText, rawSignature string) str
 		}
 	}
 	if cache.HasValidSignature(modelName, clientSignature) {
+		if targetProvider == sigcompat.SignatureProviderClaude {
+			signature, ok := sigcompat.CompatibleAntigravityClaudeThinkingSignature(clientSignature)
+			if !ok {
+				return ""
+			}
+			return signature
+		}
 		return clientSignature
 	}
 
@@ -50,9 +73,23 @@ func resolveCacheModeSignature(modelName, thinkingText, rawSignature string) str
 }
 
 func resolveBypassModeSignature(rawSignature string) string {
+	return resolveBypassModeSignatureForProvider(sigcompat.SignatureProviderClaude, rawSignature)
+}
+
+func resolveBypassModeSignatureForProvider(targetProvider sigcompat.SignatureProvider, rawSignature string) string {
 	if rawSignature == "" {
 		return ""
 	}
+	if targetProvider != sigcompat.SignatureProviderClaude && targetProvider != sigcompat.SignatureProviderUnknown {
+		return ""
+	}
+	if targetProvider == sigcompat.SignatureProviderClaude {
+		signature, ok := sigcompat.CompatibleAntigravityClaudeThinkingSignature(rawSignature)
+		if !ok {
+			return ""
+		}
+		return signature
+	}
 	normalized, err := normalizeClaudeBypassSignature(rawSignature)
 	if err != nil {
 		return ""
@@ -61,12 +98,143 @@ func resolveBypassModeSignature(rawSignature string) string {
 }
 
 func hasResolvedThinkingSignature(modelName, signature string) bool {
+	targetProvider := sigcompat.SignatureProviderFromModelName(modelName)
+	if targetProvider == sigcompat.SignatureProviderClaude {
+		_, ok := sigcompat.CompatibleAntigravityClaudeThinkingSignature(signature)
+		return ok
+	}
+	if _, ok := sigcompat.CompatibleSignatureForProvider(targetProvider, signature); ok {
+		return true
+	}
 	if cache.SignatureCacheEnabled() {
 		return cache.HasValidSignature(modelName, signature)
 	}
 	return signature != ""
 }
 
+func resolveProviderCompatibleSignature(targetProvider sigcompat.SignatureProvider, rawSignature string, blockKind sigcompat.SignatureBlockKind) string {
+	if rawSignature == "" {
+		return ""
+	}
+	if targetProvider == sigcompat.SignatureProviderClaude {
+		signature, ok := sigcompat.CompatibleAntigravityClaudeThinkingSignature(rawSignature)
+		if !ok {
+			return ""
+		}
+		return signature
+	}
+	signature, ok := sigcompat.CompatibleSignatureForProviderBlock(targetProvider, rawSignature, blockKind)
+	if !ok {
+		return ""
+	}
+	return signature
+}
+
+func resolveToolUseThoughtSignature(modelName string, contentResult gjson.Result, allowSyntheticFallback bool) string {
+	targetProvider := sigcompat.SignatureProviderFromModelName(modelName)
+	if targetProvider == sigcompat.SignatureProviderGemini {
+		for _, path := range []string{
+			"signature",
+			"thought_signature",
+			"extra_content.google.thought_signature",
+		} {
+			if signatureResult := contentResult.Get(path); signatureResult.Exists() {
+				if signature := resolveProviderCompatibleSignature(targetProvider, signatureResult.String(), sigcompat.SignatureBlockKindGeminiFunctionCall); signature != "" {
+					return signature
+				}
+			}
+		}
+		if allowSyntheticFallback {
+			return sigcompat.GeminiSkipThoughtSignatureValidator
+		}
+		return ""
+	}
+
+	for _, path := range []string{
+		"signature",
+		"thought_signature",
+		"extra_content.google.thought_signature",
+	} {
+		if signatureResult := contentResult.Get(path); signatureResult.Exists() {
+			if signature := resolveProviderCompatibleSignature(targetProvider, signatureResult.String(), sigcompat.SignatureBlockKindUnknown); signature != "" {
+				return signature
+			}
+		}
+	}
+	if targetProvider == sigcompat.SignatureProviderClaude {
+		return ""
+	}
+	return sigcompat.GeminiSkipThoughtSignatureValidator
+}
+
+func firstToolUseSignatureField(contentResult gjson.Result) (string, string, bool) {
+	for _, path := range []string{
+		"signature",
+		"thought_signature",
+		"extra_content.google.thought_signature",
+	} {
+		signatureResult := contentResult.Get(path)
+		if signatureResult.Exists() {
+			return path, signatureResult.String(), true
+		}
+	}
+	return "", "", false
+}
+
+func logDroppedAntigravityThinkingSignature(modelName string, messageIndex, contentIndex int, thinkingText string, signatureResult gjson.Result) {
+	rawSignature := signatureResult.String()
+	fields := log.Fields{
+		"component":        "signature_sanitizer",
+		"translator":       "antigravity_claude",
+		"target_provider":  string(sigcompat.SignatureProviderFromModelName(modelName)),
+		"action":           "drop_thinking_block",
+		"reason":           "missing_or_incompatible_signature",
+		"model":            modelName,
+		"message_index":    messageIndex,
+		"content_index":    contentIndex,
+		"thinking_length":  len(thinkingText),
+		"has_signature":    signatureResult.Exists(),
+		"signature_length": len(strings.TrimSpace(rawSignature)),
+	}
+	if signatureResult.Exists() {
+		fields["detected_provider"] = string(sigcompat.DetectSignatureProviderForBlock(rawSignature, sigcompat.SignatureBlockKindClaudeThinking))
+	}
+	log.WithFields(fields).Debug("antigravity claude translator: dropped thinking block with incompatible signature")
+}
+
+func logDroppedAntigravityEmptyThinking(modelName string, messageIndex, contentIndex int) {
+	log.WithFields(log.Fields{
+		"component":       "signature_sanitizer",
+		"translator":      "antigravity_claude",
+		"target_provider": string(sigcompat.SignatureProviderFromModelName(modelName)),
+		"action":          "drop_thinking_block",
+		"reason":          "empty_thinking_text",
+		"model":           modelName,
+		"message_index":   messageIndex,
+		"content_index":   contentIndex,
+	}).Debug("antigravity claude translator: dropped empty thinking block")
+}
+
+func logDroppedAntigravityToolUseSignature(modelName string, messageIndex, contentIndex int, contentResult gjson.Result) {
+	path, rawSignature, ok := firstToolUseSignatureField(contentResult)
+	if !ok {
+		return
+	}
+	log.WithFields(log.Fields{
+		"component":         "signature_sanitizer",
+		"translator":        "antigravity_claude",
+		"target_provider":   string(sigcompat.SignatureProviderFromModelName(modelName)),
+		"action":            "drop_tool_use_signature",
+		"reason":            "missing_or_incompatible_signature",
+		"model":             modelName,
+		"message_index":     messageIndex,
+		"content_index":     contentIndex,
+		"signature_path":    path,
+		"signature_length":  len(strings.TrimSpace(rawSignature)),
+		"detected_provider": string(sigcompat.DetectSignatureProviderForBlock(rawSignature, sigcompat.SignatureBlockKindUnknown)),
+	}).Debug("antigravity claude translator: dropped tool_use signature field")
+}
+
 // ConvertClaudeRequestToAntigravity parses and transforms a Claude Code API request into Gemini CLI API format.
 // It extracts the model name, system instruction, message contents, and tool declarations
 // from the raw JSON request and returns them in the format expected by the Gemini CLI API.
@@ -147,19 +315,14 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 			if contentsResult.IsArray() {
 				contentResults := contentsResult.Array()
 				numContents := len(contentResults)
-				var currentMessageThinkingSignature string
 				for j := 0; j < numContents; j++ {
 					contentResult := contentResults[j]
 					contentTypeResult := contentResult.Get("type")
 					if contentTypeResult.Type == gjson.String && contentTypeResult.String() == "thinking" {
 						// Use GetThinkingText to handle wrapped thinking objects
 						thinkingText := thinking.GetThinkingText(contentResult)
-						signature := resolveThinkingSignature(modelName, thinkingText, contentResult.Get("signature").String())
-
-						// Store for subsequent tool_use in the same message
-						if hasResolvedThinkingSignature(modelName, signature) {
-							currentMessageThinkingSignature = signature
-						}
+						signatureResult := contentResult.Get("signature")
+						signature := resolveThinkingSignature(modelName, thinkingText, signatureResult.String())
 
 						// Skip unsigned thinking blocks instead of converting them to text.
 						isUnsigned := !hasResolvedThinkingSignature(modelName, signature)
@@ -168,7 +331,7 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 						// Claude requires assistant messages to start with thinking blocks when thinking is enabled
 						// Converting to text would break this requirement
 						if isUnsigned {
-							// log.Debugf("Dropping unsigned thinking block (no valid signature)")
+							logDroppedAntigravityThinkingSignature(modelName, i, j, thinkingText, signatureResult)
 							enableThoughtTranslate = false
 							continue
 						}
@@ -178,6 +341,7 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 						// omits the required inner "thinking" field, causing:
 						//   400 "messages.N.content.0.thinking.thinking: Field required"
 						if thinkingText == "" {
+							logDroppedAntigravityEmptyThinking(modelName, i, j)
 							continue
 						}
 
@@ -226,15 +390,11 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 						if argsRaw != "" {
 							partJSON := []byte(`{}`)
 
-							// Use skip_thought_signature_validator for tool calls without valid thinking signature
-							// This is the approach used in opencode-google-antigravity-auth for Gemini
-							// and also works for Claude through Antigravity API
-							const skipSentinel = "skip_thought_signature_validator"
-							if hasResolvedThinkingSignature(modelName, currentMessageThinkingSignature) {
-								partJSON, _ = sjson.SetBytes(partJSON, "thoughtSignature", currentMessageThinkingSignature)
+							signature := resolveToolUseThoughtSignature(modelName, contentResult, true)
+							if signature != "" {
+								partJSON, _ = sjson.SetBytes(partJSON, "thoughtSignature", signature)
 							} else {
-								// No valid signature - use skip sentinel to bypass validation
-								partJSON, _ = sjson.SetBytes(partJSON, "thoughtSignature", skipSentinel)
+								logDroppedAntigravityToolUseSignature(modelName, i, j, contentResult)
 							}
 
 							if functionID != "" {

internal/translator/antigravity/claude/antigravity_claude_request_test.go

@@ -3,10 +3,13 @@ package claude
 import (
 	"bytes"
 	"encoding/base64"
+	"fmt"
 	"strings"
 	"testing"
 
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/cache"
+	log "github.com/sirupsen/logrus"
+	"github.com/sirupsen/logrus/hooks/test"
 	"github.com/tidwall/gjson"
 	"google.golang.org/protobuf/encoding/protowire"
 )
@@ -22,6 +25,13 @@ func testAnthropicNativeSignature(t *testing.T) string {
 	return signature
 }
 
+func testAntigravityClaudeSignature(t *testing.T) (string, string) {
+	t.Helper()
+
+	native := testAnthropicNativeSignature(t)
+	return native, base64.StdEncoding.EncodeToString([]byte(native))
+}
+
 func testMinimalAnthropicSignature(t *testing.T) string {
 	t.Helper()
 
@@ -70,6 +80,37 @@ func uint64Ptr(v uint64) *uint64 {
 	return &v
 }
 
+func newSignatureDebugHook(t *testing.T) *test.Hook {
+	t.Helper()
+
+	previousLevel := log.GetLevel()
+	log.SetLevel(log.DebugLevel)
+	hook := test.NewLocal(log.StandardLogger())
+	t.Cleanup(func() {
+		hook.Reset()
+		log.SetLevel(previousLevel)
+	})
+	return hook
+}
+
+func assertSignatureDebugDoesNotLeak(t *testing.T, hook *test.Hook, forbidden string) {
+	t.Helper()
+
+	if forbidden == "" {
+		return
+	}
+	for _, entry := range hook.AllEntries() {
+		if strings.Contains(entry.Message, forbidden) {
+			t.Fatalf("debug log leaked signature in message: %q", entry.Message)
+		}
+		for key, value := range entry.Data {
+			if strings.Contains(fmt.Sprint(value), forbidden) {
+				t.Fatalf("debug log leaked signature in field %q: %v", key, value)
+			}
+		}
+	}
+}
+
 func TestConvertClaudeRequestToAntigravity_StripsClaudeCodeAttribution(t *testing.T) {
 	inputJSON := []byte(`{
 		"model": "claude-sonnet-4-5",
@@ -114,6 +155,23 @@ func testGeminiRawSignature(t *testing.T) string {
 	return signature
 }
 
+func testGeminiEPrefixSignature(t *testing.T) string {
+	t.Helper()
+
+	inner := []byte{}
+	inner = protowire.AppendTag(inner, 1, protowire.BytesType)
+	inner = protowire.AppendBytes(inner, []byte{0x01, 0x0c, 0x39, 0xd6, 0xc7, 0x34})
+
+	payload := []byte{}
+	payload = protowire.AppendTag(payload, 2, protowire.BytesType)
+	payload = protowire.AppendBytes(payload, inner)
+	signature := base64.StdEncoding.EncodeToString(payload)
+	if !strings.HasPrefix(signature, "E") {
+		t.Fatalf("test signature should start with E, got %q", signature[:1])
+	}
+	return signature
+}
+
 func TestConvertClaudeRequestToAntigravity_BasicStructure(t *testing.T) {
 	inputJSON := []byte(`{
 		"model": "claude-3-5-sonnet-20240620",
@@ -182,8 +240,7 @@ func TestConvertClaudeRequestToAntigravity_RoleMapping(t *testing.T) {
 func TestConvertClaudeRequestToAntigravity_ThinkingBlocks(t *testing.T) {
 	cache.ClearSignatureCache("")
 
-	// Valid signature must be at least 50 characters
-	validSignature := "abc123validSignature1234567890123456789012345678901234567890"
+	nativeSignature, antigravitySignature := testAntigravityClaudeSignature(t)
 	thinkingText := "Let me think..."
 
 	// Pre-cache the signature (simulating a previous response for the same thinking text)
@@ -197,14 +254,14 @@ func TestConvertClaudeRequestToAntigravity_ThinkingBlocks(t *testing.T) {
 			{
 				"role": "assistant",
 				"content": [
-					{"type": "thinking", "thinking": "` + thinkingText + `", "signature": "` + validSignature + `"},
+						{"type": "thinking", "thinking": "` + thinkingText + `", "signature": "` + nativeSignature + `"},
 					{"type": "text", "text": "Answer"}
 				]
 			}
 		]
 	}`)
 
-	cache.CacheSignature("claude-sonnet-4-5-thinking", thinkingText, validSignature)
+	cache.CacheSignature("claude-sonnet-4-5-thinking", thinkingText, nativeSignature)
 
 	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5-thinking", inputJSON, false)
 	outputStr := string(output)
@@ -217,8 +274,8 @@ func TestConvertClaudeRequestToAntigravity_ThinkingBlocks(t *testing.T) {
 	if firstPart.Get("text").String() != thinkingText {
 		t.Error("thinking text mismatch")
 	}
-	if firstPart.Get("thoughtSignature").String() != validSignature {
-		t.Errorf("Expected thoughtSignature '%s', got '%s'", validSignature, firstPart.Get("thoughtSignature").String())
+	if firstPart.Get("thoughtSignature").String() != antigravitySignature {
+		t.Errorf("Expected thoughtSignature '%s', got '%s'", antigravitySignature, firstPart.Get("thoughtSignature").String())
 	}
 }
 
@@ -563,7 +620,7 @@ func TestConvertClaudeRequestToAntigravity_BypassModeNormalizesESignature(t *tes
 	})
 
 	thinkingText := "Let me think..."
-	cachedSignature := "cachedSignature1234567890123456789012345678901234567890123"
+	cachedSignature := base64.StdEncoding.EncodeToString([]byte(testMinimalAnthropicSignature(t)))
 	rawSignature := testAnthropicNativeSignature(t)
 	expectedSignature := base64.StdEncoding.EncodeToString([]byte(rawSignature))
 
@@ -750,6 +807,57 @@ func TestConvertClaudeRequestToAntigravity_BypassModeDropsInvalidSignature(t *te
 	}
 }
 
+func TestConvertClaudeRequestToAntigravity_LogsDroppedInvalidThinkingSignature(t *testing.T) {
+	cache.ClearSignatureCache("")
+	previous := cache.SignatureCacheEnabled()
+	cache.SetSignatureCacheEnabled(false)
+	t.Cleanup(func() {
+		cache.SetSignatureCacheEnabled(previous)
+		cache.ClearSignatureCache("")
+	})
+
+	hook := newSignatureDebugHook(t)
+	invalidRawSignature := testNonAnthropicRawSignature(t)
+	inputJSON := []byte(`{
+		"model": "claude-sonnet-4-5-thinking",
+		"messages": [
+			{
+				"role": "assistant",
+				"content": [
+					{"type": "thinking", "thinking": "Let me think...", "signature": "` + invalidRawSignature + `"},
+					{"type": "text", "text": "Answer"}
+				]
+			}
+		]
+	}`)
+
+	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5-thinking", inputJSON, false)
+	parts := gjson.GetBytes(output, "request.contents.0.parts").Array()
+	if len(parts) != 1 || parts[0].Get("text").String() != "Answer" {
+		t.Fatalf("expected invalid thinking block to be dropped, output: %s", output)
+	}
+
+	found := false
+	for _, entry := range hook.AllEntries() {
+		if entry.Level != log.DebugLevel {
+			continue
+		}
+		if entry.Data["component"] != "signature_sanitizer" ||
+			entry.Data["translator"] != "antigravity_claude" ||
+			entry.Data["action"] != "drop_thinking_block" {
+			continue
+		}
+		if entry.Data["model"] != "claude-sonnet-4-5-thinking" {
+			t.Fatalf("model field = %v, want claude-sonnet-4-5-thinking", entry.Data["model"])
+		}
+		found = true
+	}
+	if !found {
+		t.Fatal("expected debug log for dropped Antigravity Claude thinking signature")
+	}
+	assertSignatureDebugDoesNotLeak(t, hook, invalidRawSignature)
+}
+
 func TestConvertClaudeRequestToAntigravity_BypassModeDropsGeminiSignature(t *testing.T) {
 	cache.ClearSignatureCache("")
 	previous := cache.SignatureCacheEnabled()
@@ -784,6 +892,42 @@ func TestConvertClaudeRequestToAntigravity_BypassModeDropsGeminiSignature(t *tes
 	}
 }
 
+func TestConvertClaudeRequestToAntigravity_BypassModeDropsGeminiEPrefixSignature(t *testing.T) {
+	cache.ClearSignatureCache("")
+	previous := cache.SignatureCacheEnabled()
+	cache.SetSignatureCacheEnabled(false)
+	t.Cleanup(func() {
+		cache.SetSignatureCacheEnabled(previous)
+		cache.ClearSignatureCache("")
+	})
+
+	geminiSig := testGeminiEPrefixSignature(t)
+	inputJSON := []byte(`{
+		"model": "claude-sonnet-4-5-thinking",
+		"messages": [
+			{
+				"role": "assistant",
+				"content": [
+					{"type": "thinking", "thinking": "hmm", "signature": "` + geminiSig + `"},
+					{"type": "text", "text": "Answer"}
+				]
+			}
+		]
+	}`)
+
+	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5-thinking", inputJSON, false)
+	parts := gjson.GetBytes(output, "request.contents.0.parts").Array()
+	if len(parts) != 1 {
+		t.Fatalf("expected Gemini E-prefix signed thinking block to be dropped, got %d parts: %s", len(parts), output)
+	}
+	if parts[0].Get("text").String() != "Answer" {
+		t.Fatalf("expected remaining text part, got %s", parts[0].Raw)
+	}
+	if strings.Contains(string(output), geminiSig) {
+		t.Fatalf("Gemini E-prefix signature should not be forwarded. Output: %s", output)
+	}
+}
+
 func TestConvertClaudeRequestToAntigravity_ThinkingBlockWithoutSignature(t *testing.T) {
 	cache.ClearSignatureCache("")
 
@@ -935,18 +1079,67 @@ func TestConvertClaudeRequestToAntigravity_ToolUse(t *testing.T) {
 	if funcCall.Get("id").String() != "call_123" {
 		t.Errorf("Expected function id 'call_123', got '%s'", funcCall.Get("id").String())
 	}
-	// Verify skip_thought_signature_validator is added (bypass for tools without valid thinking)
-	expectedSig := "skip_thought_signature_validator"
-	actualSig := parts[0].Get("thoughtSignature").String()
-	if actualSig != expectedSig {
-		t.Errorf("Expected thoughtSignature '%s', got '%s'", expectedSig, actualSig)
+	if parts[0].Get("thoughtSignature").Exists() {
+		t.Errorf("Expected no thoughtSignature without valid Claude thinking signature, got '%s'", parts[0].Get("thoughtSignature").String())
 	}
 }
 
-func TestConvertClaudeRequestToAntigravity_ToolUse_WithSignature(t *testing.T) {
+func TestConvertClaudeRequestToAntigravity_ToolUse_DropsInvalidThoughtSignatureOnly(t *testing.T) {
+	hook := newSignatureDebugHook(t)
+	rawSignature := "skip_thought_signature_validator"
+	inputJSON := []byte(`{
+		"model": "claude-sonnet-4-5",
+		"messages": [
+			{
+				"role": "assistant",
+				"content": [
+					{
+						"type": "tool_use",
+						"id": "call_123",
+						"name": "get_weather",
+						"input": "{\"location\": \"Paris\"}",
+						"signature": "` + rawSignature + `"
+					}
+				]
+			}
+		]
+	}`)
+
+	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5", inputJSON, false)
+	part := gjson.GetBytes(output, "request.contents.0.parts.0")
+
+	if !part.Get("functionCall").Exists() {
+		t.Fatalf("functionCall should be preserved, output: %s", output)
+	}
+	if got := part.Get("functionCall.name").String(); got != "get_weather" {
+		t.Fatalf("functionCall.name = %q, want get_weather", got)
+	}
+	if part.Get("thoughtSignature").Exists() {
+		t.Fatalf("invalid thoughtSignature should be removed, output: %s", output)
+	}
+
+	found := false
+	for _, entry := range hook.AllEntries() {
+		if entry.Level != log.DebugLevel {
+			continue
+		}
+		if entry.Data["component"] != "signature_sanitizer" ||
+			entry.Data["translator"] != "antigravity_claude" ||
+			entry.Data["action"] != "drop_tool_use_signature" {
+			continue
+		}
+		found = true
+	}
+	if !found {
+		t.Fatal("expected debug log for dropped Antigravity Claude tool_use signature")
+	}
+	assertSignatureDebugDoesNotLeak(t, hook, rawSignature)
+}
+
+func TestConvertClaudeRequestToAntigravity_ToolUse_DoesNotReuseThinkingSignature(t *testing.T) {
 	cache.ClearSignatureCache("")
 
-	validSignature := "abc123validSignature1234567890123456789012345678901234567890"
+	nativeSignature, _ := testAntigravityClaudeSignature(t)
 	thinkingText := "Let me think..."
 
 	inputJSON := []byte(`{
@@ -959,7 +1152,7 @@ func TestConvertClaudeRequestToAntigravity_ToolUse_WithSignature(t *testing.T) {
 			{
 				"role": "assistant",
 				"content": [
-					{"type": "thinking", "thinking": "` + thinkingText + `", "signature": "` + validSignature + `"},
+						{"type": "thinking", "thinking": "` + thinkingText + `", "signature": "` + nativeSignature + `"},
 					{
 						"type": "tool_use",
 						"id": "call_123",
@@ -971,18 +1164,17 @@ func TestConvertClaudeRequestToAntigravity_ToolUse_WithSignature(t *testing.T) {
 		]
 	}`)
 
-	cache.CacheSignature("claude-sonnet-4-5-thinking", thinkingText, validSignature)
+	cache.CacheSignature("claude-sonnet-4-5-thinking", thinkingText, nativeSignature)
 
 	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5-thinking", inputJSON, false)
 	outputStr := string(output)
 
-	// Check function call has the signature from the preceding thinking block (now in contents.1)
 	part := gjson.Get(outputStr, "request.contents.1.parts.1")
 	if part.Get("functionCall.name").String() != "get_weather" {
 		t.Errorf("Expected functionCall, got %s", part.Raw)
 	}
-	if part.Get("thoughtSignature").String() != validSignature {
-		t.Errorf("Expected thoughtSignature '%s' on tool_use, got '%s'", validSignature, part.Get("thoughtSignature").String())
+	if part.Get("thoughtSignature").Exists() {
+		t.Fatalf("tool_use should not reuse preceding thinking thoughtSignature, output: %s", output)
 	}
 }
 
@@ -990,7 +1182,7 @@ func TestConvertClaudeRequestToAntigravity_ReorderThinking(t *testing.T) {
 	cache.ClearSignatureCache("")
 
 	// Case: text block followed by thinking block -> should be reordered to thinking first
-	validSignature := "abc123validSignature1234567890123456789012345678901234567890"
+	nativeSignature, _ := testAntigravityClaudeSignature(t)
 	thinkingText := "Planning..."
 
 	inputJSON := []byte(`{
@@ -1004,13 +1196,13 @@ func TestConvertClaudeRequestToAntigravity_ReorderThinking(t *testing.T) {
 				"role": "assistant",
 				"content": [
 					{"type": "text", "text": "Here is the plan."},
-					{"type": "thinking", "thinking": "` + thinkingText + `", "signature": "` + validSignature + `"}
+						{"type": "thinking", "thinking": "` + thinkingText + `", "signature": "` + nativeSignature + `"}
 				]
 			}
 		]
 	}`)
 
-	cache.CacheSignature("claude-sonnet-4-5-thinking", thinkingText, validSignature)
+	cache.CacheSignature("claude-sonnet-4-5-thinking", thinkingText, nativeSignature)
 
 	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5-thinking", inputJSON, false)
 	outputStr := string(output)
@@ -1137,7 +1329,7 @@ func TestConvertClaudeRequestToAntigravity_ReorderParallelFunctionCalls(t *testi
 func TestConvertClaudeRequestToAntigravity_ReorderThinkingAndTextBeforeFunctionCall(t *testing.T) {
 	cache.ClearSignatureCache("")
 
-	validSignature := "abc123validSignature1234567890123456789012345678901234567890"
+	nativeSignature, _ := testAntigravityClaudeSignature(t)
 	thinkingText := "Let me think about this..."
 
 	inputJSON := []byte(`{
@@ -1151,7 +1343,7 @@ func TestConvertClaudeRequestToAntigravity_ReorderThinkingAndTextBeforeFunctionC
 				"role": "assistant",
 				"content": [
 					{"type": "text", "text": "Before thinking"},
-					{"type": "thinking", "thinking": "` + thinkingText + `", "signature": "` + validSignature + `"},
+						{"type": "thinking", "thinking": "` + thinkingText + `", "signature": "` + nativeSignature + `"},
 					{
 						"type": "tool_use",
 						"id": "call_xyz",
@@ -1164,7 +1356,7 @@ func TestConvertClaudeRequestToAntigravity_ReorderThinkingAndTextBeforeFunctionC
 		]
 	}`)
 
-	cache.CacheSignature("claude-sonnet-4-5-thinking", thinkingText, validSignature)
+	cache.CacheSignature("claude-sonnet-4-5-thinking", thinkingText, nativeSignature)
 
 	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5-thinking", inputJSON, false)
 	outputStr := string(output)
@@ -1536,7 +1728,7 @@ func TestConvertClaudeRequestToAntigravity_TrailingSignedThinking_Kept(t *testin
 	cache.ClearSignatureCache("")
 
 	// Last assistant message ends with signed thinking block - should be kept
-	validSignature := "abc123validSignature1234567890123456789012345678901234567890"
+	nativeSignature, _ := testAntigravityClaudeSignature(t)
 	thinkingText := "Valid thinking..."
 
 	inputJSON := []byte(`{
@@ -1550,13 +1742,13 @@ func TestConvertClaudeRequestToAntigravity_TrailingSignedThinking_Kept(t *testin
 				"role": "assistant",
 				"content": [
 					{"type": "text", "text": "Here is my answer"},
-					{"type": "thinking", "thinking": "` + thinkingText + `", "signature": "` + validSignature + `"}
+						{"type": "thinking", "thinking": "` + thinkingText + `", "signature": "` + nativeSignature + `"}
 				]
 			}
 		]
 	}`)
 
-	cache.CacheSignature("claude-sonnet-4-5-thinking", thinkingText, validSignature)
+	cache.CacheSignature("claude-sonnet-4-5-thinking", thinkingText, nativeSignature)
 
 	output := ConvertClaudeRequestToAntigravity("claude-sonnet-4-5-thinking", inputJSON, false)
 	outputStr := string(output)

internal/translator/antigravity/claude/signature_validation.go

@@ -17,6 +17,10 @@ func StripEmptySignatureThinkingBlocks(payload []byte) []byte {
 	return signature.StripInvalidClaudeThinkingBlocks(payload, signature.ClaudeSignatureValidationOptions{PrefixOnly: true})
 }
 
+func StripInvalidBypassSignatureThinkingBlocks(payload []byte) []byte {
+	return signature.StripInvalidClaudeThinkingBlocks(payload, claudeBypassSignatureValidationOptions())
+}
+
 func ValidateClaudeBypassSignatures(inputRawJSON []byte) error {
 	return signature.ValidateClaudeThinkingSignatures(inputRawJSON, claudeBypassSignatureValidationOptions())
 }

internal/translator/antigravity/gemini/antigravity_gemini_request.go

@@ -6,9 +6,11 @@
 package gemini
 
 import (
+	"encoding/json"
 	"fmt"
 	"strings"
 
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/translator/gemini/common"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	log "github.com/sirupsen/logrus"
@@ -98,28 +100,213 @@ func ConvertGeminiRequestToAntigravity(modelName string, inputRawJSON []byte, _
 		}
 	}
 
-	// Gemini-specific handling for non-Claude models:
-	// - Replace client-provided thoughtSignature values with the skip sentinel.
-	// - Add the same sentinel to functionCall and thinking parts so upstream can bypass signature validation.
-	if !strings.Contains(strings.ToLower(modelName), "claude") {
-		const skipSentinel = "skip_thought_signature_validator"
-
-		gjson.GetBytes(rawJSON, "request.contents").ForEach(func(contentIdx, content gjson.Result) bool {
-			if content.Get("role").String() == "model" {
-				content.Get("parts").ForEach(func(partIdx, part gjson.Result) bool {
-					if part.Get("functionCall").Exists() || part.Get("thought").Exists() || part.Get("thoughtSignature").Exists() {
-						rawJSON, _ = sjson.SetBytes(rawJSON, fmt.Sprintf("request.contents.%d.parts.%d.thoughtSignature", contentIdx.Int(), partIdx.Int()), skipSentinel)
-					}
-					return true
-				})
-			}
-			return true
-		})
+	if strings.Contains(strings.ToLower(modelName), "claude") {
+		rawJSON = sanitizeAntigravityClaudeGeminiRequestSignatures(modelName, rawJSON)
+	} else {
+		rawJSON = signature.SanitizeGeminiRequestThoughtSignatures(rawJSON, "request.contents")
 	}
 
 	return common.AttachDefaultSafetySettings(rawJSON, "request.safetySettings")
 }
 
+func sanitizeAntigravityClaudeGeminiRequestSignatures(modelName string, rawJSON []byte) []byte {
+	var root map[string]any
+	if err := json.Unmarshal(rawJSON, &root); err != nil {
+		log.WithError(err).Debug("antigravity gemini translator: failed to parse request for Claude signature sanitize")
+		return rawJSON
+	}
+
+	request, ok := root["request"].(map[string]any)
+	if !ok {
+		return rawJSON
+	}
+	contents, ok := request["contents"].([]any)
+	if !ok {
+		return rawJSON
+	}
+
+	changed := false
+	rewrittenContents := make([]any, 0, len(contents))
+	for contentIndex, contentValue := range contents {
+		content, ok := contentValue.(map[string]any)
+		if !ok {
+			rewrittenContents = append(rewrittenContents, contentValue)
+			continue
+		}
+
+		parts, ok := content["parts"].([]any)
+		if !ok {
+			rewrittenContents = append(rewrittenContents, content)
+			continue
+		}
+
+		isModelTurn := content["role"] == "model"
+		rewrittenParts := make([]any, 0, len(parts))
+		for partIndex, partValue := range parts {
+			part, ok := partValue.(map[string]any)
+			if !ok {
+				rewrittenParts = append(rewrittenParts, partValue)
+				continue
+			}
+
+			rawSignature, hasSignature := antigravityClaudeGeminiPartThoughtSignature(part)
+			if hasFunctionResponsePart(part) {
+				if hasSignature {
+					changed = true
+					deleteAntigravityClaudeGeminiPartThoughtSignatureFields(part)
+					logAntigravityClaudeGeminiSignatureSanitize(modelName, "drop_signature", "functionResponse parts cannot replay Claude thinking signatures", contentIndex, partIndex, rawSignature)
+				}
+				rewrittenParts = append(rewrittenParts, part)
+				continue
+			}
+			if !isModelTurn {
+				if hasSignature {
+					changed = true
+					deleteAntigravityClaudeGeminiPartThoughtSignatureFields(part)
+					logAntigravityClaudeGeminiSignatureSanitize(modelName, "drop_signature", "non-model parts cannot replay Claude thinking signatures", contentIndex, partIndex, rawSignature)
+				}
+				rewrittenParts = append(rewrittenParts, part)
+				continue
+			}
+
+			if part["thought"] == true {
+				normalized, compatible := signature.CompatibleAntigravityClaudeThinkingSignature(rawSignature)
+				if !compatible {
+					changed = true
+					logAntigravityClaudeGeminiSignatureSanitize(modelName, "drop_thinking_block", "missing_or_incompatible_signature", contentIndex, partIndex, rawSignature)
+					continue
+				}
+				if text, _ := part["text"].(string); strings.TrimSpace(text) == "" {
+					changed = true
+					logAntigravityClaudeGeminiSignatureSanitize(modelName, "drop_thinking_block", "empty_thinking_text", contentIndex, partIndex, rawSignature)
+					continue
+				}
+				if normalized != rawSignature {
+					changed = true
+					logAntigravityClaudeGeminiSignatureSanitize(modelName, "normalize_signature", "compatible_claude_signature", contentIndex, partIndex, rawSignature)
+				}
+				deleteAntigravityClaudeGeminiPartThoughtSignatureFields(part)
+				part["thoughtSignature"] = normalized
+				rewrittenParts = append(rewrittenParts, part)
+				continue
+			}
+
+			if hasSignature {
+				changed = true
+				deleteAntigravityClaudeGeminiPartThoughtSignatureFields(part)
+				logAntigravityClaudeGeminiSignatureSanitize(modelName, "drop_signature", "non-thinking parts should not carry Claude thinking signatures", contentIndex, partIndex, rawSignature)
+			}
+			rewrittenParts = append(rewrittenParts, part)
+		}
+
+		if len(rewrittenParts) == 0 {
+			changed = true
+			continue
+		}
+		content["parts"] = rewrittenParts
+		rewrittenContents = append(rewrittenContents, content)
+	}
+
+	if !changed {
+		return rawJSON
+	}
+	request["contents"] = rewrittenContents
+	out, err := json.Marshal(root)
+	if err != nil {
+		log.WithError(err).Debug("antigravity gemini translator: failed to marshal Claude signature sanitize")
+		return rawJSON
+	}
+	return out
+}
+
+func antigravityClaudeGeminiPartThoughtSignature(part map[string]any) (string, bool) {
+	for _, path := range [][]string{
+		{"thoughtSignature"},
+		{"thought_signature"},
+		{"functionCall", "thoughtSignature"},
+		{"functionCall", "thought_signature"},
+		{"functionResponse", "thoughtSignature"},
+		{"functionResponse", "thought_signature"},
+		{"extra_content", "google", "thought_signature"},
+	} {
+		if value, ok := stringAtPath(part, path...); ok {
+			return value, true
+		}
+	}
+	return "", false
+}
+
+func deleteAntigravityClaudeGeminiPartThoughtSignatureFields(part map[string]any) {
+	for _, path := range [][]string{
+		{"thoughtSignature"},
+		{"thought_signature"},
+		{"functionCall", "thoughtSignature"},
+		{"functionCall", "thought_signature"},
+		{"functionResponse", "thoughtSignature"},
+		{"functionResponse", "thought_signature"},
+		{"extra_content", "google", "thought_signature"},
+	} {
+		deleteAtPath(part, path...)
+	}
+}
+
+func hasFunctionResponsePart(part map[string]any) bool {
+	_, ok := part["functionResponse"]
+	if ok {
+		return true
+	}
+	_, ok = part["function_response"]
+	return ok
+}
+
+func stringAtPath(value map[string]any, path ...string) (string, bool) {
+	var current any = value
+	for _, key := range path {
+		m, ok := current.(map[string]any)
+		if !ok {
+			return "", false
+		}
+		current, ok = m[key]
+		if !ok {
+			return "", false
+		}
+	}
+	s, ok := current.(string)
+	return s, ok
+}
+
+func deleteAtPath(value map[string]any, path ...string) {
+	if len(path) == 0 {
+		return
+	}
+	current := value
+	for _, key := range path[:len(path)-1] {
+		next, ok := current[key].(map[string]any)
+		if !ok {
+			return
+		}
+		current = next
+	}
+	delete(current, path[len(path)-1])
+}
+
+func logAntigravityClaudeGeminiSignatureSanitize(modelName, action, reason string, contentIndex, partIndex int, rawSignature string) {
+	fields := log.Fields{
+		"component":         "signature_sanitizer",
+		"translator":        "antigravity_gemini",
+		"target_provider":   string(signature.SignatureProviderClaude),
+		"action":            action,
+		"reason":            reason,
+		"model":             modelName,
+		"content_index":     contentIndex,
+		"part_index":        partIndex,
+		"has_signature":     strings.TrimSpace(rawSignature) != "",
+		"signature_length":  len(strings.TrimSpace(rawSignature)),
+		"detected_provider": string(signature.DetectSignatureProviderForBlock(rawSignature, signature.SignatureBlockKindClaudeThinking)),
+	}
+	log.WithFields(fields).Debug("antigravity gemini translator: sanitized Claude target thoughtSignature before upstream")
+}
+
 // FunctionCallGroup represents a group of function calls and their responses
 type FunctionCallGroup struct {
 	ResponsesNeeded int

internal/translator/antigravity/gemini/antigravity_gemini_request_test.go

@@ -1,10 +1,13 @@
 package gemini
 
 import (
+	"encoding/base64"
 	"fmt"
 	"testing"
 
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/tidwall/gjson"
+	"google.golang.org/protobuf/encoding/protowire"
 )
 
 func TestConvertGeminiRequestToAntigravity_ReplacesClientSignatureOnFunctionCall(t *testing.T) {
@@ -105,6 +108,128 @@ func TestConvertGeminiRequestToAntigravity_SkipsUppercaseClaudeModel(t *testing.
 	}
 }
 
+func TestConvertGeminiRequestToAntigravity_ClaudeModelNormalizesStrictClaudeThoughtSignature(t *testing.T) {
+	nativeSig := testAntigravityGeminiClaudeSignature(t)
+	expectedSig, ok := signature.CompatibleAntigravityClaudeThinkingSignature(nativeSig)
+	if !ok {
+		t.Fatal("test Claude signature should be compatible with Antigravity Claude")
+	}
+
+	inputJSON := []byte(`{
+		"model": "claude-opus-4-6-thinking",
+		"contents": [
+			{
+				"role": "model",
+				"parts": [
+					{"text": "internal reasoning", "thought": true, "thoughtSignature": "` + nativeSig + `"},
+					{"text": "visible answer"}
+				]
+			},
+			{
+				"role": "user",
+				"parts": [{"text": "continue"}]
+			}
+		]
+	}`)
+
+	output := ConvertGeminiRequestToAntigravity("claude-opus-4-6-thinking", inputJSON, false)
+
+	part := gjson.GetBytes(output, "request.contents.0.parts.0")
+	if !part.Get("thought").Bool() {
+		t.Fatalf("first part should remain thought. Output: %s", output)
+	}
+	if got := part.Get("thoughtSignature").String(); got != expectedSig {
+		t.Fatalf("thoughtSignature = %q, want %q. Output: %s", got, expectedSig, output)
+	}
+}
+
+func TestConvertGeminiRequestToAntigravity_ClaudeModelDropsNonStrictEPrefixThoughtSignature(t *testing.T) {
+	looseEPrefix := base64.StdEncoding.EncodeToString([]byte{0x12, 0x01, 0x02})
+	if looseEPrefix[0] != 'E' {
+		t.Fatalf("test signature should start with E, got %q", looseEPrefix[:1])
+	}
+
+	inputJSON := []byte(`{
+		"model": "claude-opus-4-6-thinking",
+		"contents": [
+			{
+				"role": "model",
+				"parts": [
+					{"text": "must not reach Claude", "thought": true, "thoughtSignature": "` + looseEPrefix + `"},
+					{"text": "visible answer"}
+				]
+			},
+			{
+				"role": "user",
+				"parts": [{"text": "continue"}]
+			}
+		]
+	}`)
+
+	output := ConvertGeminiRequestToAntigravity("claude-opus-4-6-thinking", inputJSON, false)
+
+	if gjson.GetBytes(output, `request.contents.#.parts.#(thought=true)#`).Int() != 0 {
+		t.Fatalf("non-strict E-prefix thought block should be dropped. Output: %s", output)
+	}
+	if got := gjson.GetBytes(output, "request.contents.0.parts.0.text").String(); got != "visible answer" {
+		t.Fatalf("visible text = %q, want visible answer. Output: %s", got, output)
+	}
+}
+
+func TestConvertGeminiRequestToAntigravity_ClaudeModelDropsEmptyThoughtText(t *testing.T) {
+	nativeSig := testAntigravityGeminiClaudeSignature(t)
+	inputJSON := []byte(`{
+		"model": "claude-opus-4-6-thinking",
+		"contents": [
+			{
+				"role": "model",
+				"parts": [
+					{"text": "", "thought": true, "thoughtSignature": "` + nativeSig + `"},
+					{"text": "visible answer"}
+				]
+			},
+			{
+				"role": "user",
+				"parts": [{"text": "continue"}]
+			}
+		]
+	}`)
+
+	output := ConvertGeminiRequestToAntigravity("claude-opus-4-6-thinking", inputJSON, false)
+
+	if gjson.GetBytes(output, `request.contents.#.parts.#(thought=true)#`).Int() != 0 {
+		t.Fatalf("empty-text thought block should be dropped for Antigravity Claude. Output: %s", output)
+	}
+	if got := gjson.GetBytes(output, "request.contents.0.parts.0.text").String(); got != "visible answer" {
+		t.Fatalf("visible text = %q, want visible answer. Output: %s", got, output)
+	}
+}
+
+func TestConvertGeminiRequestToAntigravity_ClaudeModelStripsUnneededFunctionCallSignature(t *testing.T) {
+	nativeSig := testAntigravityGeminiClaudeSignature(t)
+	inputJSON := []byte(`{
+		"model": "claude-opus-4-6-thinking",
+		"contents": [
+			{
+				"role": "model",
+				"parts": [
+					{"functionCall": {"name": "test_tool", "args": {}}, "thoughtSignature": "` + nativeSig + `"}
+				]
+			}
+		]
+	}`)
+
+	output := ConvertGeminiRequestToAntigravity("claude-opus-4-6-thinking", inputJSON, false)
+
+	part := gjson.GetBytes(output, "request.contents.0.parts.0")
+	if !part.Get("functionCall").Exists() {
+		t.Fatalf("functionCall should be preserved. Output: %s", output)
+	}
+	if part.Get("thoughtSignature").Exists() {
+		t.Fatalf("functionCall thoughtSignature should be stripped for Claude target. Output: %s", output)
+	}
+}
+
 func TestConvertGeminiRequestToAntigravity_AddSkipSentinelToFunctionCall(t *testing.T) {
 	// functionCall without signature should get skip_thought_signature_validator
 	inputJSON := []byte(`{
@@ -130,6 +255,28 @@ func TestConvertGeminiRequestToAntigravity_AddSkipSentinelToFunctionCall(t *test
 	}
 }
 
+func testAntigravityGeminiClaudeSignature(t *testing.T) string {
+	t.Helper()
+	channelBlock := []byte{}
+	channelBlock = protowire.AppendTag(channelBlock, 1, protowire.VarintType)
+	channelBlock = protowire.AppendVarint(channelBlock, 12)
+	channelBlock = protowire.AppendTag(channelBlock, 2, protowire.VarintType)
+	channelBlock = protowire.AppendVarint(channelBlock, 2)
+	channelBlock = protowire.AppendTag(channelBlock, 6, protowire.BytesType)
+	channelBlock = protowire.AppendString(channelBlock, "claude-sonnet-4-6")
+
+	container := []byte{}
+	container = protowire.AppendTag(container, 1, protowire.BytesType)
+	container = protowire.AppendBytes(container, channelBlock)
+
+	payload := []byte{}
+	payload = protowire.AppendTag(payload, 2, protowire.BytesType)
+	payload = protowire.AppendBytes(payload, container)
+	payload = protowire.AppendTag(payload, 3, protowire.VarintType)
+	payload = protowire.AppendVarint(payload, 1)
+	return base64.StdEncoding.EncodeToString(payload)
+}
+
 func TestConvertGeminiRequestToAntigravity_ParallelFunctionCalls(t *testing.T) {
 	// Multiple functionCalls should all get skip_thought_signature_validator
 	inputJSON := []byte(`{

internal/translator/antigravity/openai/responses/antigravity_openai-responses_request.go

@@ -1,12 +1,204 @@
 package responses
 
 import (
+	"encoding/json"
+	"strings"
+
+	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	. "github.com/router-for-me/CLIProxyAPI/v7/internal/translator/antigravity/gemini"
 	. "github.com/router-for-me/CLIProxyAPI/v7/internal/translator/gemini/openai/responses"
+	log "github.com/sirupsen/logrus"
+	"github.com/tidwall/gjson"
 )
 
 func ConvertOpenAIResponsesRequestToAntigravity(modelName string, inputRawJSON []byte, stream bool) []byte {
 	rawJSON := inputRawJSON
 	rawJSON = ConvertOpenAIResponsesRequestToGemini(modelName, rawJSON, stream)
+	rawJSON = rewriteOpenAIResponsesReasoningForAntigravityClaude(modelName, inputRawJSON, rawJSON)
 	return ConvertGeminiRequestToAntigravity(modelName, rawJSON, stream)
 }
+
+type antigravityClaudeReasoningSignature struct {
+	Signature        string
+	HasRawSignature  bool
+	RawSignatureLen  int
+	DetectedProvider sigcompat.SignatureProvider
+}
+
+func rewriteOpenAIResponsesReasoningForAntigravityClaude(modelName string, inputRawJSON, geminiJSON []byte) []byte {
+	if sigcompat.SignatureProviderFromModelName(modelName) != sigcompat.SignatureProviderClaude {
+		return geminiJSON
+	}
+
+	reasoningSignatures := antigravityClaudeReasoningSignatures(inputRawJSON)
+	if len(reasoningSignatures) == 0 {
+		return geminiJSON
+	}
+
+	var root map[string]any
+	if err := json.Unmarshal(geminiJSON, &root); err != nil {
+		log.WithError(err).Debug("antigravity responses translator: failed to parse Gemini request for Claude signature rewrite")
+		return geminiJSON
+	}
+
+	contents, ok := root["contents"].([]any)
+	if !ok {
+		return geminiJSON
+	}
+
+	reasoningIndex := 0
+	changed := false
+	rewrittenContents := make([]any, 0, len(contents))
+	for contentIndex, contentValue := range contents {
+		content, ok := contentValue.(map[string]any)
+		if !ok {
+			rewrittenContents = append(rewrittenContents, contentValue)
+			continue
+		}
+
+		parts, ok := content["parts"].([]any)
+		if !ok {
+			rewrittenContents = append(rewrittenContents, content)
+			continue
+		}
+
+		rewrittenParts := make([]any, 0, len(parts))
+		for partIndex, partValue := range parts {
+			part, ok := partValue.(map[string]any)
+			if !ok || part["thought"] != true {
+				rewrittenParts = append(rewrittenParts, partValue)
+				continue
+			}
+
+			var reasoningSig antigravityClaudeReasoningSignature
+			if reasoningIndex < len(reasoningSignatures) {
+				reasoningSig = reasoningSignatures[reasoningIndex]
+			}
+			reasoningIndex++
+
+			if reasoningSig.Signature == "" {
+				changed = true
+				logDroppedOpenAIResponsesAntigravityClaudeReasoning(modelName, contentIndex, partIndex, reasoningIndex-1, reasoningSig)
+				continue
+			}
+			if text, _ := part["text"].(string); strings.TrimSpace(text) == "" {
+				changed = true
+				logDroppedOpenAIResponsesAntigravityClaudeEmptyReasoning(modelName, contentIndex, partIndex, reasoningIndex-1, reasoningSig)
+				continue
+			}
+
+			if currentSignature, _ := part["thoughtSignature"].(string); currentSignature != reasoningSig.Signature {
+				changed = true
+				logNormalizedOpenAIResponsesAntigravityClaudeReasoning(modelName, contentIndex, partIndex, reasoningIndex-1, reasoningSig)
+			}
+			part["thoughtSignature"] = reasoningSig.Signature
+			rewrittenParts = append(rewrittenParts, part)
+		}
+
+		if len(rewrittenParts) == 0 {
+			changed = true
+			continue
+		}
+		content["parts"] = rewrittenParts
+		rewrittenContents = append(rewrittenContents, content)
+	}
+
+	if !changed {
+		return geminiJSON
+	}
+
+	root["contents"] = rewrittenContents
+	out, err := json.Marshal(root)
+	if err != nil {
+		log.WithError(err).Debug("antigravity responses translator: failed to marshal Claude signature rewrite")
+		return geminiJSON
+	}
+	return out
+}
+
+func antigravityClaudeReasoningSignatures(inputRawJSON []byte) []antigravityClaudeReasoningSignature {
+	input := gjson.GetBytes(inputRawJSON, "input")
+	if !input.IsArray() {
+		return nil
+	}
+
+	signatures := make([]antigravityClaudeReasoningSignature, 0)
+	input.ForEach(func(_, item gjson.Result) bool {
+		itemType := item.Get("type").String()
+		if itemType == "" && item.Get("role").Exists() {
+			itemType = "message"
+		}
+		if itemType != "reasoning" {
+			return true
+		}
+
+		rawSignatureResult := item.Get("encrypted_content")
+		rawSignature := rawSignatureResult.String()
+		signature, ok := sigcompat.CompatibleAntigravityClaudeThinkingSignature(rawSignature)
+		reasoningSignature := antigravityClaudeReasoningSignature{
+			HasRawSignature:  rawSignatureResult.Exists(),
+			RawSignatureLen:  len(rawSignature),
+			DetectedProvider: sigcompat.SignatureProviderUnknown,
+		}
+		if rawSignature != "" {
+			reasoningSignature.DetectedProvider = sigcompat.DetectSignatureProviderForBlock(rawSignature, sigcompat.SignatureBlockKindClaudeThinking)
+		}
+		if ok {
+			reasoningSignature.Signature = signature
+		}
+		signatures = append(signatures, reasoningSignature)
+		return true
+	})
+	return signatures
+}
+
+func logDroppedOpenAIResponsesAntigravityClaudeReasoning(modelName string, contentIndex, partIndex, reasoningIndex int, sig antigravityClaudeReasoningSignature) {
+	log.WithFields(log.Fields{
+		"component":         "signature_sanitizer",
+		"translator":        "antigravity_openai_responses",
+		"target_provider":   string(sigcompat.SignatureProviderClaude),
+		"action":            "drop_thinking_block",
+		"reason":            "missing_or_incompatible_signature",
+		"model":             modelName,
+		"content_index":     contentIndex,
+		"part_index":        partIndex,
+		"reasoning_index":   reasoningIndex,
+		"has_signature":     sig.HasRawSignature,
+		"signature_length":  sig.RawSignatureLen,
+		"detected_provider": string(sig.DetectedProvider),
+	}).Debug("antigravity responses translator: dropped Claude reasoning block with incompatible encrypted_content")
+}
+
+func logDroppedOpenAIResponsesAntigravityClaudeEmptyReasoning(modelName string, contentIndex, partIndex, reasoningIndex int, sig antigravityClaudeReasoningSignature) {
+	log.WithFields(log.Fields{
+		"component":         "signature_sanitizer",
+		"translator":        "antigravity_openai_responses",
+		"target_provider":   string(sigcompat.SignatureProviderClaude),
+		"action":            "drop_thinking_block",
+		"reason":            "empty_thinking_text",
+		"model":             modelName,
+		"content_index":     contentIndex,
+		"part_index":        partIndex,
+		"reasoning_index":   reasoningIndex,
+		"has_signature":     sig.HasRawSignature,
+		"signature_length":  sig.RawSignatureLen,
+		"detected_provider": string(sig.DetectedProvider),
+	}).Debug("antigravity responses translator: dropped Claude reasoning block with empty thinking text")
+}
+
+func logNormalizedOpenAIResponsesAntigravityClaudeReasoning(modelName string, contentIndex, partIndex, reasoningIndex int, sig antigravityClaudeReasoningSignature) {
+	log.WithFields(log.Fields{
+		"component":         "signature_sanitizer",
+		"translator":        "antigravity_openai_responses",
+		"target_provider":   string(sigcompat.SignatureProviderClaude),
+		"action":            "normalize_signature",
+		"reason":            "compatible_claude_signature",
+		"model":             modelName,
+		"content_index":     contentIndex,
+		"part_index":        partIndex,
+		"reasoning_index":   reasoningIndex,
+		"has_signature":     sig.HasRawSignature,
+		"signature_length":  sig.RawSignatureLen,
+		"detected_provider": string(sig.DetectedProvider),
+	}).Debug("antigravity responses translator: normalized Claude reasoning encrypted_content before upstream")
+}

internal/translator/antigravity/openai/responses/antigravity_openai-responses_request_test.go

@@ -0,0 +1,176 @@
+package responses
+
+import (
+	"encoding/base64"
+	"strings"
+	"testing"
+
+	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
+	"github.com/tidwall/gjson"
+	"google.golang.org/protobuf/encoding/protowire"
+)
+
+func TestConvertOpenAIResponsesRequestToAntigravity_ClaudeReasoningKeepsClaudeSignature(t *testing.T) {
+	nativeSig := testAntigravityResponsesClaudeSignature(t)
+	antigravitySig, ok := sigcompat.CompatibleAntigravityClaudeThinkingSignature(nativeSig)
+	if !ok {
+		t.Fatal("test Claude signature should be compatible with Antigravity Claude")
+	}
+
+	tests := []struct {
+		name      string
+		encrypted string
+	}{
+		{
+			name:      "Claude native E signature",
+			encrypted: nativeSig,
+		},
+		{
+			name:      "Antigravity double-layer R signature",
+			encrypted: antigravitySig,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			raw := []byte(`{
+				"model": "claude-opus-4-6-thinking",
+				"input": [
+					{
+						"id": "rs_prev",
+						"type": "reasoning",
+						"encrypted_content": "` + tt.encrypted + `",
+						"summary": [{"type": "summary_text", "text": "internal reasoning"}]
+					},
+					{
+						"role": "assistant",
+						"content": [{"type": "output_text", "text": "visible answer"}]
+					},
+					{
+						"role": "user",
+						"content": [{"type": "input_text", "text": "continue"}]
+					}
+				]
+			}`)
+
+			out := ConvertOpenAIResponsesRequestToAntigravity("claude-opus-4-6-thinking", raw, false)
+			part := gjson.GetBytes(out, "request.contents.0.parts.0")
+			if !part.Get("thought").Bool() {
+				t.Fatalf("first part should remain a thought block. Output: %s", out)
+			}
+			if got := part.Get("thoughtSignature").String(); got != antigravitySig {
+				t.Fatalf("thoughtSignature prefix/len = %q/%d, want %q/%d. Output: %s",
+					firstByte(got), len(got), firstByte(antigravitySig), len(antigravitySig), out)
+			}
+			if got := part.Get("text").String(); got != "internal reasoning" {
+				t.Fatalf("thought text = %q, want internal reasoning. Output: %s", got, out)
+			}
+		})
+	}
+}
+
+func TestConvertOpenAIResponsesRequestToAntigravity_ClaudeReasoningDropsIncompatibleSignature(t *testing.T) {
+	raw := []byte(`{
+		"model": "claude-opus-4-6-thinking",
+		"input": [
+			{
+				"id": "rs_prev",
+				"type": "reasoning",
+				"encrypted_content": "` + testAntigravityResponsesGPTSignature() + `",
+				"summary": [{"type": "summary_text", "text": "must not reach Claude"}]
+			},
+			{
+				"role": "assistant",
+				"content": [{"type": "output_text", "text": "visible answer"}]
+			},
+			{
+				"role": "user",
+				"content": [{"type": "input_text", "text": "continue"}]
+			}
+		]
+	}`)
+
+	out := ConvertOpenAIResponsesRequestToAntigravity("claude-opus-4-6-thinking", raw, false)
+	if strings.Contains(string(out), sigcompat.GeminiSkipThoughtSignatureValidator) {
+		t.Fatalf("Claude target must not receive Gemini bypass signature. Output: %s", out)
+	}
+	if gjson.GetBytes(out, `request.contents.#.parts.#(thought=true)#`).Int() != 0 {
+		t.Fatalf("incompatible reasoning block should be dropped. Output: %s", out)
+	}
+	if strings.Contains(string(out), "must not reach Claude") {
+		t.Fatalf("incompatible reasoning text should be dropped. Output: %s", out)
+	}
+	if got := gjson.GetBytes(out, "request.contents.0.parts.0.text").String(); got != "visible answer" {
+		t.Fatalf("visible assistant text = %q, want visible answer. Output: %s", got, out)
+	}
+}
+
+func TestConvertOpenAIResponsesRequestToAntigravity_ClaudeReasoningDropsEmptyThinkingText(t *testing.T) {
+	rawSignature := testAntigravityResponsesClaudeSignature(t)
+	raw := []byte(`{
+		"model": "claude-opus-4-6-thinking",
+		"input": [
+			{
+				"id": "rs_prev",
+				"type": "reasoning",
+				"encrypted_content": "` + rawSignature + `",
+				"summary": []
+			},
+			{
+				"role": "assistant",
+				"content": [{"type": "output_text", "text": "visible answer"}]
+			},
+			{
+				"role": "user",
+				"content": [{"type": "input_text", "text": "continue"}]
+			}
+		]
+	}`)
+
+	out := ConvertOpenAIResponsesRequestToAntigravity("claude-opus-4-6-thinking", raw, false)
+	if gjson.GetBytes(out, `request.contents.#.parts.#(thought=true)#`).Int() != 0 {
+		t.Fatalf("empty-text reasoning block should be dropped for Antigravity Claude. Output: %s", out)
+	}
+	if got := gjson.GetBytes(out, "request.contents.0.parts.0.text").String(); got != "visible answer" {
+		t.Fatalf("visible assistant text = %q, want visible answer. Output: %s", got, out)
+	}
+}
+
+func testAntigravityResponsesClaudeSignature(t *testing.T) string {
+	t.Helper()
+	channelBlock := []byte{}
+	channelBlock = protowire.AppendTag(channelBlock, 1, protowire.VarintType)
+	channelBlock = protowire.AppendVarint(channelBlock, 12)
+	channelBlock = protowire.AppendTag(channelBlock, 2, protowire.VarintType)
+	channelBlock = protowire.AppendVarint(channelBlock, 2)
+	channelBlock = protowire.AppendTag(channelBlock, 6, protowire.BytesType)
+	channelBlock = protowire.AppendString(channelBlock, "claude-sonnet-4-6")
+
+	container := []byte{}
+	container = protowire.AppendTag(container, 1, protowire.BytesType)
+	container = protowire.AppendBytes(container, channelBlock)
+
+	payload := []byte{}
+	payload = protowire.AppendTag(payload, 2, protowire.BytesType)
+	payload = protowire.AppendBytes(payload, container)
+	payload = protowire.AppendTag(payload, 3, protowire.VarintType)
+	payload = protowire.AppendVarint(payload, 1)
+	return base64.StdEncoding.EncodeToString(payload)
+}
+
+func testAntigravityResponsesGPTSignature() string {
+	payload := make([]byte, 1+8+16+16+32)
+	payload[0] = 0x80
+	payload[8] = 1
+	for i := 9; i < len(payload); i++ {
+		payload[i] = byte(i)
+	}
+	return base64.URLEncoding.EncodeToString(payload)
+}
+
+func firstByte(s string) string {
+	if s == "" {
+		return ""
+	}
+	return s[:1]
+}

internal/translator/claude/openai/responses/claude_openai-responses_request.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/google/uuid"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/registry"
+	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking"
 	"github.com/tidwall/gjson"
 	"github.com/tidwall/sjson"
@@ -439,8 +440,8 @@ func ConvertOpenAIResponsesRequestToClaude(modelName string, inputRawJSON []byte
 }
 
 func convertResponsesReasoningToClaudeThinking(item gjson.Result) []byte {
-	signature := item.Get("encrypted_content").String()
-	if signature == "" {
+	signature, ok := sigcompat.CompatibleSignatureForProvider(sigcompat.SignatureProviderClaude, item.Get("encrypted_content").String())
+	if !ok {
 		return nil
 	}
 

internal/translator/claude/openai/responses/claude_openai-responses_request_test.go

@@ -1,19 +1,22 @@
 package responses
 
 import (
+	"encoding/base64"
 	"testing"
 
+	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/tidwall/gjson"
+	"google.golang.org/protobuf/encoding/protowire"
 )
 
 func TestConvertOpenAIResponsesRequestToClaude_ReasoningItemToThinkingBlock(t *testing.T) {
-	signature := "claude_sig_request"
+	rawSignature, expectedSignature := testClaudeResponsesThinkingSignature(t)
 	raw := []byte(`{
 		"model":"claude-test",
 		"input":[
 			{
 				"type":"reasoning",
-				"encrypted_content":"` + signature + `",
+				"encrypted_content":"` + rawSignature + `",
 				"summary":[{"type":"summary_text","text":"internal reasoning"}]
 			},
 			{
@@ -39,8 +42,8 @@ func TestConvertOpenAIResponsesRequestToClaude_ReasoningItemToThinkingBlock(t *t
 	if got := assistant.Get("content.0.type").String(); got != "thinking" {
 		t.Fatalf("first content type = %q, want thinking. Output: %s", got, string(out))
 	}
-	if got := assistant.Get("content.0.signature").String(); got != signature {
-		t.Fatalf("thinking signature = %q, want %q", got, signature)
+	if got := assistant.Get("content.0.signature").String(); got != expectedSignature {
+		t.Fatalf("thinking signature = %q, want %q", got, expectedSignature)
 	}
 	if got := assistant.Get("content.0.thinking").String(); got != "internal reasoning" {
 		t.Fatalf("thinking text = %q, want internal reasoning", got)
@@ -57,13 +60,13 @@ func TestConvertOpenAIResponsesRequestToClaude_ReasoningItemToThinkingBlock(t *t
 }
 
 func TestConvertOpenAIResponsesRequestToClaude_SignatureOnlyReasoningFlushesBeforeUser(t *testing.T) {
-	signature := "claude_sig_only"
+	rawSignature, expectedSignature := testClaudeResponsesThinkingSignature(t)
 	raw := []byte(`{
 		"model":"claude-test",
 		"input":[
 			{
 				"type":"reasoning",
-				"encrypted_content":"` + signature + `",
+				"encrypted_content":"` + rawSignature + `",
 				"summary":[]
 			},
 			{
@@ -81,8 +84,8 @@ func TestConvertOpenAIResponsesRequestToClaude_SignatureOnlyReasoningFlushesBefo
 	if got := thinking.Get("type").String(); got != "thinking" {
 		t.Fatalf("first content type = %q, want thinking. Output: %s", got, string(out))
 	}
-	if got := thinking.Get("signature").String(); got != signature {
-		t.Fatalf("thinking signature = %q, want %q", got, signature)
+	if got := thinking.Get("signature").String(); got != expectedSignature {
+		t.Fatalf("thinking signature = %q, want %q", got, expectedSignature)
 	}
 	if got := thinking.Get("thinking").String(); got != "" {
 		t.Fatalf("thinking text = %q, want empty", got)
@@ -91,3 +94,71 @@ func TestConvertOpenAIResponsesRequestToClaude_SignatureOnlyReasoningFlushesBefo
 		t.Fatalf("second message role = %q, want user. Output: %s", got, string(out))
 	}
 }
+
+func TestConvertOpenAIResponsesRequestToClaude_DropsIncompatibleReasoningSignature(t *testing.T) {
+	raw := []byte(`{
+		"model":"claude-test",
+		"input":[
+			{
+				"type":"reasoning",
+				"encrypted_content":"` + testGPTResponsesReasoningSignature() + `",
+				"summary":[{"type":"summary_text","text":"must not become Claude thinking"}]
+			},
+			{
+				"type":"message",
+				"role":"user",
+				"content":[{"type":"input_text","text":"continue"}]
+			}
+		]
+	}`)
+
+	out := ConvertOpenAIResponsesRequestToClaude("claude-test", raw, false)
+
+	if gjson.GetBytes(out, "messages.0.content.0.type").String() == "thinking" {
+		t.Fatalf("GPT encrypted_content should not become Claude thinking. Output: %s", string(out))
+	}
+	if gjson.GetBytes(out, "messages.0.content.0.signature").Exists() {
+		t.Fatalf("incompatible signature should not be forwarded. Output: %s", string(out))
+	}
+	if got := gjson.GetBytes(out, "messages.0.role").String(); got != "user" {
+		t.Fatalf("first message role = %q, want user. Output: %s", got, string(out))
+	}
+}
+
+func testClaudeResponsesThinkingSignature(t *testing.T) (string, string) {
+	t.Helper()
+	channelBlock := []byte{}
+	channelBlock = protowire.AppendTag(channelBlock, 1, protowire.VarintType)
+	channelBlock = protowire.AppendVarint(channelBlock, 12)
+	channelBlock = protowire.AppendTag(channelBlock, 2, protowire.VarintType)
+	channelBlock = protowire.AppendVarint(channelBlock, 2)
+	channelBlock = protowire.AppendTag(channelBlock, 6, protowire.BytesType)
+	channelBlock = protowire.AppendString(channelBlock, "claude-sonnet-4-6")
+
+	container := []byte{}
+	container = protowire.AppendTag(container, 1, protowire.BytesType)
+	container = protowire.AppendBytes(container, channelBlock)
+
+	payload := []byte{}
+	payload = protowire.AppendTag(payload, 2, protowire.BytesType)
+	payload = protowire.AppendBytes(payload, container)
+	payload = protowire.AppendTag(payload, 3, protowire.VarintType)
+	payload = protowire.AppendVarint(payload, 1)
+
+	rawSignature := base64.StdEncoding.EncodeToString(payload)
+	normalized, ok := sigcompat.CompatibleSignatureForProvider(sigcompat.SignatureProviderClaude, rawSignature)
+	if !ok {
+		t.Fatal("test Claude signature should be compatible")
+	}
+	return rawSignature, normalized
+}
+
+func testGPTResponsesReasoningSignature() string {
+	payload := make([]byte, 1+8+16+16+32)
+	payload[0] = 0x80
+	payload[8] = 1
+	for i := 9; i < len(payload); i++ {
+		payload[i] = byte(i)
+	}
+	return base64.URLEncoding.EncodeToString(payload)
+}

internal/translator/codex/claude/codex_claude_request.go

@@ -7,12 +7,12 @@ package claude
 
 import (
 	"crypto/sha256"
-	"encoding/base64"
 	"encoding/hex"
 	"fmt"
 	"strconv"
 	"strings"
 
+	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	"github.com/tidwall/gjson"
@@ -133,8 +133,8 @@ func ConvertClaudeRequestToCodex(modelName string, inputRawJSON []byte, _ bool)
 					return
 				}
 
-				signature := part.Get("signature").String()
-				if !isFernetLikeReasoningSignature(signature) {
+				signature, ok := sigcompat.CompatibleSignatureForProvider(sigcompat.SignatureProviderGPT, part.Get("signature").String())
+				if !ok {
 					return
 				}
 
@@ -334,39 +334,6 @@ func ConvertClaudeRequestToCodex(modelName string, inputRawJSON []byte, _ bool)
 	return template
 }
 
-// isFernetLikeReasoningSignature checks only the encrypted_content envelope shape
-// observed in OpenAI reasoning signatures. It does not authenticate source or payload type.
-func isFernetLikeReasoningSignature(signature string) bool {
-	const (
-		fernetVersionLen = 1
-		fernetTimestamp  = 8
-		fernetIV         = 16
-		fernetHMAC       = 32
-		aesBlockSize     = 16
-	)
-
-	signature = strings.TrimSpace(signature)
-	if !strings.HasPrefix(signature, "gAAAA") {
-		return false
-	}
-
-	decoded, err := base64.URLEncoding.DecodeString(signature)
-	if err != nil {
-		decoded, err = base64.RawURLEncoding.DecodeString(signature)
-		if err != nil {
-			return false
-		}
-	}
-
-	minLen := fernetVersionLen + fernetTimestamp + fernetIV + aesBlockSize + fernetHMAC
-	if len(decoded) < minLen || decoded[0] != 0x80 {
-		return false
-	}
-
-	ciphertextLen := len(decoded) - fernetVersionLen - fernetTimestamp - fernetIV - fernetHMAC
-	return ciphertextLen > 0 && ciphertextLen%aesBlockSize == 0
-}
-
 // shortenCodexCallIDIfNeeded keeps Claude tool IDs within the OpenAI Responses
 // API call_id limit while preserving a stable, low-collision mapping.
 func shortenCodexCallIDIfNeeded(id string) string {

internal/translator/gemini-cli/gemini/gemini-cli_gemini_request.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"strings"
 
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/translator/gemini/common"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	log "github.com/sirupsen/logrus"
@@ -97,19 +98,7 @@ func ConvertGeminiRequestToGeminiCLI(_ string, inputRawJSON []byte, _ bool) []by
 		}
 	}
 
-	gjson.GetBytes(rawJSON, "request.contents").ForEach(func(key, content gjson.Result) bool {
-		if content.Get("role").String() == "model" {
-			content.Get("parts").ForEach(func(partKey, part gjson.Result) bool {
-				if part.Get("functionCall").Exists() {
-					rawJSON, _ = sjson.SetBytes(rawJSON, fmt.Sprintf("request.contents.%d.parts.%d.thoughtSignature", key.Int(), partKey.Int()), "skip_thought_signature_validator")
-				} else if part.Get("thoughtSignature").Exists() {
-					rawJSON, _ = sjson.SetBytes(rawJSON, fmt.Sprintf("request.contents.%d.parts.%d.thoughtSignature", key.Int(), partKey.Int()), "skip_thought_signature_validator")
-				}
-				return true
-			})
-		}
-		return true
-	})
+	rawJSON = signature.SanitizeGeminiRequestThoughtSignatures(rawJSON, "request.contents")
 
 	// Filter out contents with empty parts to avoid Gemini API error:
 	// "required oneof field 'data' must have one initialized field"

internal/translator/gemini-cli/openai/chat-completions/gemini-cli_openai_request.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/misc"
+	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/translator/gemini/common"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	log "github.com/sirupsen/logrus"
@@ -255,7 +256,7 @@ func ConvertOpenAIRequestToGeminiCLI(modelName string, inputRawJSON []byte, _ bo
 						fargs := tc.Get("function.arguments").String()
 						node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".functionCall.name", fname)
 						node, _ = sjson.SetRawBytes(node, "parts."+itoa(p)+".functionCall.args", []byte(fargs))
-						node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".thoughtSignature", geminiCLIFunctionThoughtSignature)
+						node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".thoughtSignature", openAIToolCallGeminiThoughtSignature(tc))
 						p++
 						if fid != "" {
 							fIDs = append(fIDs, fid)
@@ -397,5 +398,19 @@ func ConvertOpenAIRequestToGeminiCLI(modelName string, inputRawJSON []byte, _ bo
 	return common.AttachDefaultSafetySettings(out, "request.safetySettings")
 }
 
+func openAIToolCallGeminiThoughtSignature(toolCall gjson.Result) string {
+	for _, path := range []string{
+		"extra_content.google.thought_signature",
+		"function.extra_content.google.thought_signature",
+		"thoughtSignature",
+		"thought_signature",
+	} {
+		if signatureResult := toolCall.Get(path); signatureResult.Exists() {
+			return sigcompat.GeminiReplaySignatureOrBypass(signatureResult.String(), sigcompat.SignatureBlockKindGeminiFunctionCall)
+		}
+	}
+	return geminiCLIFunctionThoughtSignature
+}
+
 // itoa converts int to string without strconv import for few usages.
 func itoa(i int) string { return fmt.Sprintf("%d", i) }

internal/translator/gemini/gemini-cli/gemini_gemini-cli_request.go

@@ -8,6 +8,7 @@ package geminiCLI
 import (
 	"fmt"
 
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/translator/gemini/common"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	"github.com/tidwall/gjson"
@@ -45,19 +46,7 @@ func ConvertGeminiCLIRequestToGemini(_ string, inputRawJSON []byte, _ bool) []by
 		}
 	}
 
-	gjson.GetBytes(rawJSON, "contents").ForEach(func(key, content gjson.Result) bool {
-		if content.Get("role").String() == "model" {
-			content.Get("parts").ForEach(func(partKey, part gjson.Result) bool {
-				if part.Get("functionCall").Exists() {
-					rawJSON, _ = sjson.SetBytes(rawJSON, fmt.Sprintf("contents.%d.parts.%d.thoughtSignature", key.Int(), partKey.Int()), "skip_thought_signature_validator")
-				} else if part.Get("thoughtSignature").Exists() {
-					rawJSON, _ = sjson.SetBytes(rawJSON, fmt.Sprintf("contents.%d.parts.%d.thoughtSignature", key.Int(), partKey.Int()), "skip_thought_signature_validator")
-				}
-				return true
-			})
-		}
-		return true
-	})
+	rawJSON = signature.SanitizeGeminiRequestThoughtSignatures(rawJSON, "contents")
 
 	return common.AttachDefaultSafetySettings(rawJSON, "safetySettings")
 }

internal/translator/gemini/gemini/gemini_gemini_request.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"strings"
 
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/translator/gemini/common"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	log "github.com/sirupsen/logrus"
@@ -78,19 +79,7 @@ func ConvertGeminiRequestToGemini(_ string, inputRawJSON []byte, _ bool) []byte
 		return true
 	})
 
-	gjson.GetBytes(out, "contents").ForEach(func(key, content gjson.Result) bool {
-		if content.Get("role").String() == "model" {
-			content.Get("parts").ForEach(func(partKey, part gjson.Result) bool {
-				if part.Get("functionCall").Exists() {
-					out, _ = sjson.SetBytes(out, fmt.Sprintf("contents.%d.parts.%d.thoughtSignature", key.Int(), partKey.Int()), "skip_thought_signature_validator")
-				} else if part.Get("thoughtSignature").Exists() {
-					out, _ = sjson.SetBytes(out, fmt.Sprintf("contents.%d.parts.%d.thoughtSignature", key.Int(), partKey.Int()), "skip_thought_signature_validator")
-				}
-				return true
-			})
-		}
-		return true
-	})
+	out = signature.SanitizeGeminiRequestThoughtSignatures(out, "contents")
 
 	if gjson.GetBytes(rawJSON, "generationConfig.responseSchema").Exists() {
 		strJson, _ := util.RenameKey(string(out), "generationConfig.responseSchema", "generationConfig.responseJsonSchema")

internal/translator/gemini/openai/chat-completions/gemini_openai_request.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/misc"
+	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/translator/gemini/common"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	log "github.com/sirupsen/logrus"
@@ -261,7 +262,7 @@ func ConvertOpenAIRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 						fargs := tc.Get("function.arguments").String()
 						node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".functionCall.name", fname)
 						node, _ = sjson.SetRawBytes(node, "parts."+itoa(p)+".functionCall.args", []byte(fargs))
-						node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".thoughtSignature", geminiFunctionThoughtSignature)
+						node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".thoughtSignature", openAIToolCallGeminiThoughtSignature(tc))
 						p++
 						if fid != "" {
 							fIDs = append(fIDs, fid)
@@ -411,5 +412,19 @@ func ConvertOpenAIRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 	return out
 }
 
+func openAIToolCallGeminiThoughtSignature(toolCall gjson.Result) string {
+	for _, path := range []string{
+		"extra_content.google.thought_signature",
+		"function.extra_content.google.thought_signature",
+		"thoughtSignature",
+		"thought_signature",
+	} {
+		if signatureResult := toolCall.Get(path); signatureResult.Exists() {
+			return sigcompat.GeminiReplaySignatureOrBypass(signatureResult.String(), sigcompat.SignatureBlockKindGeminiFunctionCall)
+		}
+	}
+	return geminiFunctionThoughtSignature
+}
+
 // itoa converts int to string without strconv import for few usages.
 func itoa(i int) string { return fmt.Sprintf("%d", i) }

internal/translator/gemini/openai/chat-completions/gemini_openai_signature_test.go

@@ -0,0 +1,51 @@
+package chat_completions
+
+import (
+	"testing"
+
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
+	"github.com/tidwall/gjson"
+)
+
+const capturedGeminiToolCallThoughtSignature = "EjQKMgEMOdbHO0Gd+c9Mxk4ELwPGbpCEcp2mFfYYLix2UVtBH3fL8GECc4+JITVnHF4qZDsA"
+
+func TestConvertOpenAIRequestToGemini_ToolCallSignatureCompatibility(t *testing.T) {
+	tests := []struct {
+		name          string
+		rawSignature  string
+		wantSignature string
+	}{
+		{
+			name:          "Gemini signature is preserved",
+			rawSignature:  "gemini#" + capturedGeminiToolCallThoughtSignature,
+			wantSignature: capturedGeminiToolCallThoughtSignature,
+		},
+		{
+			name:          "unknown signature uses bypass",
+			rawSignature:  "not-a-provider-signature",
+			wantSignature: signature.GeminiSkipThoughtSignatureValidator,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			input := []byte(`{
+				"model": "gemini-3.5-flash",
+				"messages": [{
+					"role": "assistant",
+					"tool_calls": [{
+						"id": "call_123",
+						"type": "function",
+						"function": {"name": "lookup", "arguments": "{\"q\":\"Paris\"}"},
+						"extra_content": {"google": {"thought_signature": "` + tt.rawSignature + `"}}
+					}]
+				}]
+			}`)
+
+			output := ConvertOpenAIRequestToGemini("gemini-3.5-flash", input, false)
+			if got := gjson.GetBytes(output, "contents.0.parts.0.thoughtSignature").String(); got != tt.wantSignature {
+				t.Fatalf("thoughtSignature = %q, want %q. Output: %s", got, tt.wantSignature, output)
+			}
+		})
+	}
+}

internal/translator/gemini/openai/responses/gemini_openai-responses_request.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"strings"
 
+	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/translator/gemini/common"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	"github.com/tidwall/gjson"
@@ -355,7 +356,7 @@ func ConvertOpenAIResponsesRequestToGemini(modelName string, inputRawJSON []byte
 				thoughtContent := []byte(`{"role":"model","parts":[]}`)
 				thought := []byte(`{"text":"","thoughtSignature":"","thought":true}`)
 				thought, _ = sjson.SetBytes(thought, "text", item.Get("summary.0.text").String())
-				thought, _ = sjson.SetBytes(thought, "thoughtSignature", item.Get("encrypted_content").String())
+				thought, _ = sjson.SetBytes(thought, "thoughtSignature", openAIResponsesGeminiThoughtSignature(item.Get("encrypted_content").String()))
 
 				thoughtContent, _ = sjson.SetRawBytes(thoughtContent, "parts.-1", thought)
 				out, _ = sjson.SetRawBytes(out, "contents.-1", thoughtContent)
@@ -454,3 +455,7 @@ func ConvertOpenAIResponsesRequestToGemini(modelName string, inputRawJSON []byte
 	result = common.AttachDefaultSafetySettings(result, "safetySettings")
 	return result
 }
+
+func openAIResponsesGeminiThoughtSignature(rawSignature string) string {
+	return sigcompat.GeminiReplaySignatureOrBypass(rawSignature, sigcompat.SignatureBlockKindGeminiModelPart)
+}

internal/translator/gemini/openai/responses/gemini_openai-responses_request_test.go

@@ -0,0 +1,66 @@
+package responses
+
+import (
+	"encoding/base64"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+const testResponsesGeminiThoughtSignature = "EjQKMgEMOdbHO0Gd+c9Mxk4ELwPGbpCEcp2mFfYYLix2UVtBH3fL8GECc4+JITVnHF4qZDsA"
+
+func TestConvertOpenAIResponsesRequestToGemini_ReasoningSignatureCompatibility(t *testing.T) {
+	tests := []struct {
+		name          string
+		encrypted     string
+		wantSignature string
+	}{
+		{
+			name:          "GPT encrypted_content uses Gemini bypass",
+			encrypted:     validResponsesGPTReasoningSignature(),
+			wantSignature: geminiResponsesThoughtSignature,
+		},
+		{
+			name:          "Gemini encrypted_content is preserved",
+			encrypted:     "gemini#" + testResponsesGeminiThoughtSignature,
+			wantSignature: testResponsesGeminiThoughtSignature,
+		},
+		{
+			name:          "Missing encrypted_content uses Gemini bypass",
+			encrypted:     "",
+			wantSignature: geminiResponsesThoughtSignature,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			input := []byte(`{
+				"model": "gpt-5",
+				"input": [{
+					"type": "reasoning",
+					"encrypted_content": "` + tt.encrypted + `",
+					"summary": [{"type": "summary_text", "text": "reasoning summary"}]
+				}]
+			}`)
+
+			output := ConvertOpenAIResponsesRequestToGemini("gemini-3.5-flash", input, false)
+			part := gjson.GetBytes(output, "contents.0.parts.0")
+			if got := part.Get("thoughtSignature").String(); got != tt.wantSignature {
+				t.Fatalf("thoughtSignature = %q, want %q. Output: %s", got, tt.wantSignature, output)
+			}
+			if got := part.Get("text").String(); got != "reasoning summary" {
+				t.Fatalf("thought text = %q, want reasoning summary. Output: %s", got, output)
+			}
+		})
+	}
+}
+
+func validResponsesGPTReasoningSignature() string {
+	raw := make([]byte, 1+8+16+16+32)
+	raw[0] = 0x80
+	raw[8] = 1
+	for i := 9; i < len(raw); i++ {
+		raw[i] = byte(i)
+	}
+	return base64.URLEncoding.EncodeToString(raw)
+}

internal/translator/openai/claude/openai_claude_request.go

@@ -8,6 +8,7 @@ package claude
 import (
 	"strings"
 
+	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	"github.com/tidwall/gjson"
@@ -147,6 +148,9 @@ func ConvertClaudeRequestToOpenAI(modelName string, inputRawJSON []byte, stream
 					case "thinking":
 						// Only map thinking to reasoning_content for assistant messages (security: prevent injection)
 						if role == "assistant" {
+							if !shouldMapClaudeThinkingToGPTReasoning(part) {
+								return true
+							}
 							thinkingText := thinking.GetThinkingText(part)
 							// Skip empty or whitespace-only thinking
 							if strings.TrimSpace(thinkingText) != "" {
@@ -329,6 +333,15 @@ func ConvertClaudeRequestToOpenAI(modelName string, inputRawJSON []byte, stream
 	return out
 }
 
+func shouldMapClaudeThinkingToGPTReasoning(part gjson.Result) bool {
+	signature := part.Get("signature")
+	if !signature.Exists() || strings.TrimSpace(signature.String()) == "" {
+		return false
+	}
+	_, ok := sigcompat.CompatibleSignatureForProvider(sigcompat.SignatureProviderGPT, signature.String())
+	return ok
+}
+
 func convertClaudeContentPart(part gjson.Result) (string, bool) {
 	partType := part.Get("type").String()
 

internal/translator/openai/claude/openai_claude_request_test.go

@@ -1,6 +1,7 @@
 package claude
 
 import (
+	"encoding/base64"
 	"testing"
 
 	"github.com/tidwall/gjson"
@@ -18,7 +19,7 @@ func TestConvertClaudeRequestToOpenAI_ThinkingToReasoningContent(t *testing.T) {
 		wantHasContent          bool
 	}{
 		{
-			name: "AC1: assistant message with thinking and text",
+			name: "AC1: unsigned assistant thinking is dropped",
 			inputJSON: `{
 				"model": "claude-3-opus",
 				"messages": [{
@@ -29,8 +30,8 @@ func TestConvertClaudeRequestToOpenAI_ThinkingToReasoningContent(t *testing.T) {
 					]
 				}]
 			}`,
-			wantReasoningContent:    "Let me analyze this step by step...",
-			wantHasReasoningContent: true,
+			wantReasoningContent:    "",
+			wantHasReasoningContent: false,
 			wantContentText:         "Here is my response.",
 			wantHasContent:          true,
 		},
@@ -52,7 +53,7 @@ func TestConvertClaudeRequestToOpenAI_ThinkingToReasoningContent(t *testing.T) {
 			wantHasContent:          true,
 		},
 		{
-			name: "AC3: thinking-only message preserved with reasoning_content",
+			name: "AC3: unsigned thinking-only message is dropped",
 			inputJSON: `{
 				"model": "claude-3-opus",
 				"messages": [{
@@ -62,11 +63,10 @@ func TestConvertClaudeRequestToOpenAI_ThinkingToReasoningContent(t *testing.T) {
 					]
 				}]
 			}`,
-			wantReasoningContent:    "Internal reasoning only.",
-			wantHasReasoningContent: true,
+			wantReasoningContent:    "",
+			wantHasReasoningContent: false,
 			wantContentText:         "",
-			// For OpenAI compatibility, content field is set to empty string "" when no text content exists
-			wantHasContent: false,
+			wantHasContent:          false,
 		},
 		{
 			name: "AC4: thinking in user role must be ignored",
@@ -139,7 +139,7 @@ func TestConvertClaudeRequestToOpenAI_ThinkingToReasoningContent(t *testing.T) {
 			wantHasContent:          true,
 		},
 		{
-			name: "Multiple thinking parts concatenated",
+			name: "Unsigned thinking parts are dropped",
 			inputJSON: `{
 				"model": "claude-3-opus",
 				"messages": [{
@@ -151,13 +151,13 @@ func TestConvertClaudeRequestToOpenAI_ThinkingToReasoningContent(t *testing.T) {
 					]
 				}]
 			}`,
-			wantReasoningContent:    "First thought.\n\nSecond thought.",
-			wantHasReasoningContent: true,
+			wantReasoningContent:    "",
+			wantHasReasoningContent: false,
 			wantContentText:         "Final answer.",
 			wantHasContent:          true,
 		},
 		{
-			name: "Mixed thinking and redacted_thinking",
+			name: "Mixed unsigned thinking and redacted_thinking",
 			inputJSON: `{
 				"model": "claude-3-opus",
 				"messages": [{
@@ -169,8 +169,8 @@ func TestConvertClaudeRequestToOpenAI_ThinkingToReasoningContent(t *testing.T) {
 					]
 				}]
 			}`,
-			wantReasoningContent:    "Visible thought.",
-			wantHasReasoningContent: true,
+			wantReasoningContent:    "",
+			wantHasReasoningContent: false,
 			wantContentText:         "Answer.",
 			wantHasContent:          true,
 		},
@@ -246,9 +246,73 @@ func TestConvertClaudeRequestToOpenAI_ThinkingToReasoningContent(t *testing.T) {
 	}
 }
 
-// TestConvertClaudeRequestToOpenAI_ThinkingOnlyMessagePreserved tests AC3:
-// that a message with only thinking content is preserved (not dropped).
-func TestConvertClaudeRequestToOpenAI_ThinkingOnlyMessagePreserved(t *testing.T) {
+func TestConvertClaudeRequestToOpenAI_SignedThinkingCompatibility(t *testing.T) {
+	tests := []struct {
+		name                    string
+		signature               string
+		wantReasoningContent    string
+		wantHasReasoningContent bool
+	}{
+		{
+			name:                    "GPT-compatible signature keeps reasoning_content",
+			signature:               validGPTChatReasoningSignature(),
+			wantReasoningContent:    "provider state",
+			wantHasReasoningContent: true,
+		},
+		{
+			name:                    "Claude signature drops reasoning_content",
+			signature:               "claude#EjQ=",
+			wantReasoningContent:    "",
+			wantHasReasoningContent: false,
+		},
+		{
+			name:                    "Gemini signature drops reasoning_content",
+			signature:               "gemini#EjQKMgEMOdbHO0Gd+c9Mxk4ELwPGbpCEcp2mFfYYLix2UVtBH3fL8GECc4+JITVnHF4qZDsA",
+			wantReasoningContent:    "",
+			wantHasReasoningContent: false,
+		},
+		{
+			name:                    "Unknown signature drops reasoning_content",
+			signature:               "not-a-provider-signature",
+			wantReasoningContent:    "",
+			wantHasReasoningContent: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			inputJSON := `{
+				"model": "claude-3-opus",
+				"messages": [{
+					"role": "assistant",
+					"content": [
+						{"type": "thinking", "thinking": "provider state", "signature": "` + tt.signature + `"},
+						{"type": "text", "text": "visible answer"}
+					]
+				}]
+			}`
+
+			result := ConvertClaudeRequestToOpenAI("gpt-5", []byte(inputJSON), false)
+			assistantMsg := gjson.GetBytes(result, "messages.0")
+			gotReasoningContent := assistantMsg.Get("reasoning_content").String()
+			gotHasReasoningContent := assistantMsg.Get("reasoning_content").Exists()
+
+			if gotHasReasoningContent != tt.wantHasReasoningContent {
+				t.Fatalf("reasoning_content exists = %v, want %v. Output: %s", gotHasReasoningContent, tt.wantHasReasoningContent, string(result))
+			}
+			if gotReasoningContent != tt.wantReasoningContent {
+				t.Fatalf("reasoning_content = %q, want %q. Output: %s", gotReasoningContent, tt.wantReasoningContent, string(result))
+			}
+			if got := assistantMsg.Get("content.0.text").String(); got != "visible answer" {
+				t.Fatalf("visible content = %q, want visible answer. Output: %s", got, string(result))
+			}
+		})
+	}
+}
+
+// TestConvertClaudeRequestToOpenAI_UnsignedThinkingOnlyMessageDropped verifies
+// that unsigned Claude thinking is not migrated into GPT reasoning state.
+func TestConvertClaudeRequestToOpenAI_UnsignedThinkingOnlyMessageDropped(t *testing.T) {
 	inputJSON := `{
 		"model": "claude-3-opus",
 		"messages": [
@@ -272,24 +336,24 @@ func TestConvertClaudeRequestToOpenAI_ThinkingOnlyMessagePreserved(t *testing.T)
 
 	messages := resultJSON.Get("messages").Array()
 
-	// Should have: user + assistant (thinking-only) + user = 3 messages
-	if len(messages) != 3 {
-		t.Fatalf("Expected 3 messages, got %d. Messages: %v", len(messages), resultJSON.Get("messages").Raw)
+	if len(messages) != 2 {
+		t.Fatalf("Expected unsigned thinking-only assistant message to be dropped, got %d. Messages: %v", len(messages), resultJSON.Get("messages").Raw)
 	}
+	for _, message := range messages {
+		if message.Get("reasoning_content").Exists() {
+			t.Fatalf("unsigned thinking should not produce reasoning_content. Messages: %v", resultJSON.Get("messages").Raw)
+		}
+	}
+}
 
-	// Check the assistant message (index 1) has reasoning_content
-	assistantMsg := messages[1]
-	if assistantMsg.Get("role").String() != "assistant" {
-		t.Errorf("Expected message[1] to be assistant, got %s", assistantMsg.Get("role").String())
-	}
-
-	if !assistantMsg.Get("reasoning_content").Exists() {
-		t.Error("Expected assistant message to have reasoning_content")
-	}
-
-	if assistantMsg.Get("reasoning_content").String() != "Let me calculate: 2+2=4" {
-		t.Errorf("Unexpected reasoning_content: %s", assistantMsg.Get("reasoning_content").String())
+func validGPTChatReasoningSignature() string {
+	raw := make([]byte, 1+8+16+16+32)
+	raw[0] = 0x80
+	raw[8] = 1
+	for i := 9; i < len(raw); i++ {
+		raw[i] = byte(i)
 	}
+	return base64.URLEncoding.EncodeToString(raw)
 }
 
 func TestConvertClaudeRequestToOpenAI_SystemMessageScenarios(t *testing.T) {
@@ -667,8 +731,7 @@ func TestConvertClaudeRequestToOpenAI_AssistantThinkingToolUseThinkingSplit(t *t
 	resultJSON := gjson.ParseBytes(result)
 	messages := resultJSON.Get("messages").Array()
 
-	// New behavior: all content, thinking, and tool_calls unified in single assistant message
-	// Expect: assistant(content[pre,post] + tool_calls + reasoning_content[t1+t2])
+	// Unsigned thinking is dropped, while text and tool_calls remain unified.
 	if len(messages) != 1 {
 		t.Fatalf("Expected 1 message, got %d. Messages: %s", len(messages), resultJSON.Get("messages").Raw)
 	}
@@ -691,9 +754,8 @@ func TestConvertClaudeRequestToOpenAI_AssistantThinkingToolUseThinkingSplit(t *t
 		t.Fatalf("Expected assistant message to have tool_calls")
 	}
 
-	// Should have combined reasoning_content from both thinking blocks
-	if got := assistantMsg.Get("reasoning_content").String(); got != "t1\n\nt2" {
-		t.Fatalf("Expected reasoning_content %q, got %q", "t1\n\nt2", got)
+	if assistantMsg.Get("reasoning_content").Exists() {
+		t.Fatalf("unsigned thinking should not produce reasoning_content: %s", assistantMsg.Raw)
 	}
 }
 

sdk/api/handlers/openai/openai_responses_signature_test.go

@@ -0,0 +1,86 @@
+package openai
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/registry"
+	"github.com/router-for-me/CLIProxyAPI/v7/sdk/api/handlers"
+	coreauth "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/auth"
+	sdkconfig "github.com/router-for-me/CLIProxyAPI/v7/sdk/config"
+)
+
+func TestOpenAIResponsesForwardsInvalidReasoningEncryptedContentToExecutor(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	executor := &compactCaptureExecutor{}
+	manager := coreauth.NewManager(nil, nil, nil)
+	manager.RegisterExecutor(executor)
+
+	auth := &coreauth.Auth{ID: "signature-auth-responses", Provider: executor.Identifier(), Status: coreauth.StatusActive}
+	if _, err := manager.Register(context.Background(), auth); err != nil {
+		t.Fatalf("Register auth: %v", err)
+	}
+	registry.GetGlobalRegistry().RegisterClient(auth.ID, auth.Provider, []*registry.ModelInfo{{ID: "test-signature-model"}})
+	t.Cleanup(func() {
+		registry.GetGlobalRegistry().UnregisterClient(auth.ID)
+	})
+
+	base := handlers.NewBaseAPIHandlers(&sdkconfig.SDKConfig{}, manager)
+	h := NewOpenAIResponsesAPIHandler(base)
+	router := gin.New()
+	router.POST("/v1/responses", h.Responses)
+
+	body := `{"model":"test-signature-model","stream":false,"input":[{"id":"rs_bad","type":"reasoning","encrypted_content":"gAAAAABqFTIa\u2026abc","summary":[]}]}`
+	req := httptest.NewRequest(http.MethodPost, "/v1/responses", strings.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	resp := httptest.NewRecorder()
+	router.ServeHTTP(resp, req)
+
+	if resp.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d; body=%s", resp.Code, http.StatusOK, resp.Body.String())
+	}
+	if executor.calls != 1 {
+		t.Fatalf("executor calls = %d, want 1", executor.calls)
+	}
+}
+
+func TestOpenAIResponsesCompactForwardsInvalidReasoningEncryptedContentToExecutor(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	executor := &compactCaptureExecutor{}
+	manager := coreauth.NewManager(nil, nil, nil)
+	manager.RegisterExecutor(executor)
+
+	auth := &coreauth.Auth{ID: "signature-auth-compact", Provider: executor.Identifier(), Status: coreauth.StatusActive}
+	if _, err := manager.Register(context.Background(), auth); err != nil {
+		t.Fatalf("Register auth: %v", err)
+	}
+	registry.GetGlobalRegistry().RegisterClient(auth.ID, auth.Provider, []*registry.ModelInfo{{ID: "test-signature-compact-model"}})
+	t.Cleanup(func() {
+		registry.GetGlobalRegistry().UnregisterClient(auth.ID)
+	})
+
+	base := handlers.NewBaseAPIHandlers(&sdkconfig.SDKConfig{}, manager)
+	h := NewOpenAIResponsesAPIHandler(base)
+	router := gin.New()
+	router.POST("/v1/responses/compact", h.Compact)
+
+	body := `{"model":"test-signature-compact-model","input":[{"id":"rs_bad","type":"reasoning","encrypted_content":"bad","summary":[]}]}`
+	req := httptest.NewRequest(http.MethodPost, "/v1/responses/compact", strings.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	resp := httptest.NewRecorder()
+	router.ServeHTTP(resp, req)
+
+	if resp.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d; body=%s", resp.Code, http.StatusOK, resp.Body.String())
+	}
+	if executor.calls != 1 {
+		t.Fatalf("executor calls = %d, want 1", executor.calls)
+	}
+	if executor.alt != "responses/compact" {
+		t.Fatalf("alt = %q, want responses/compact", executor.alt)
+	}
+}