diff --git a/internal/signature/gemini_sanitize.go b/internal/signature/gemini_sanitize.go
index e639255c..9678c46d 100644
--- a/internal/signature/gemini_sanitize.go
+++ b/internal/signature/gemini_sanitize.go
@@ -1,7 +1,6 @@
 package signature
 
 import (
-	"fmt"
 	"strings"
 
 	log "github.com/sirupsen/logrus"
@@ -34,23 +33,29 @@ func SanitizeGeminiRequestThoughtSignatures(payload []byte, contentsPath string)
 	}
 
 	contents := gjson.GetBytes(payload, contentsPath)
-	if !contents.IsArray() {
+	if !contents.IsArray() || !geminiContentsThoughtSignaturesNeedSanitize(contents) {
 		return payload
 	}
 
+	contentsChanged := false
+	contentItems := make([][]byte, 0, int(contents.Get("#").Int()))
 	contents.ForEach(func(contentIdx, content gjson.Result) bool {
-		isModelTurn := content.Get("role").String() == "model"
 		parts := content.Get("parts")
 		if !parts.IsArray() {
+			contentItems = append(contentItems, []byte(content.Raw))
 			return true
 		}
 
+		isModelTurn := content.Get("role").String() == "model"
+		partsChanged := false
+		partItems := make([][]byte, 0, int(parts.Get("#").Int()))
 		parts.ForEach(func(partIdx, part gjson.Result) bool {
-			partPath := fmt.Sprintf("%s.%d.parts.%d", contentsPath, contentIdx.Int(), partIdx.Int())
+			partJSON := []byte(part.Raw)
 			if part.Get("functionResponse").Exists() {
 				_, hadSignature := geminiPartThoughtSignature(part)
-				payload = deleteGeminiPartThoughtSignatureFields(payload, partPath)
 				if hadSignature {
+					partJSON = deleteGeminiPartThoughtSignatureFields(partJSON)
+					partsChanged = true
 					logGeminiThoughtSignatureSanitize(contentsPath, int(contentIdx.Int()), int(partIdx.Int()), SignatureCompatibilityDecision{
 						TargetProvider: SignatureProviderGemini,
 						BlockKind:      SignatureBlockKindGeminiModelPart,
@@ -58,9 +63,11 @@ func SanitizeGeminiRequestThoughtSignatures(payload []byte, contentsPath string)
 						Reason:         "user-turn functionResponse parts cannot replay thought signatures",
 					}, "", true)
 				}
+				partItems = append(partItems, partJSON)
 				return true
 			}
 			if !isModelTurn {
+				partItems = append(partItems, partJSON)
 				return true
 			}
 
@@ -68,6 +75,7 @@ func SanitizeGeminiRequestThoughtSignatures(payload []byte, contentsPath string)
 			hasThought := part.Get("thought").Exists()
 			rawSignature, hasSignature := geminiPartThoughtSignature(part)
 			if !hasFunctionCall && !hasThought && !hasSignature {
+				partItems = append(partItems, partJSON)
 				return true
 			}
 
@@ -75,19 +83,72 @@ func SanitizeGeminiRequestThoughtSignatures(payload []byte, contentsPath string)
 			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 !hasNormalizedGeminiPartThoughtSignature(part, replaySignature) {
+				partJSON = deleteGeminiPartThoughtSignatureFields(partJSON)
+				partJSON, _ = sjson.SetBytes(partJSON, "thoughtSignature", replaySignature)
+				partsChanged = true
+			}
 			if decision.Action != SignatureActionPreserve {
 				logGeminiThoughtSignatureSanitize(contentsPath, int(contentIdx.Int()), int(partIdx.Int()), decision, rawSignature, hasSignature)
 			}
+			partItems = append(partItems, partJSON)
 			return true
 		})
+
+		contentJSON := []byte(content.Raw)
+		if partsChanged {
+			contentJSON, _ = sjson.SetRawBytes(contentJSON, "parts", joinGeminiSignatureRawArray(partItems))
+			contentsChanged = true
+		}
+		contentItems = append(contentItems, contentJSON)
 		return true
 	})
 
-	return payload
+	if !contentsChanged {
+		return payload
+	}
+	updated, errSet := sjson.SetRawBytes(payload, contentsPath, joinGeminiSignatureRawArray(contentItems))
+	if errSet != nil {
+		return payload
+	}
+	return updated
+}
+
+func geminiContentsThoughtSignaturesNeedSanitize(contents gjson.Result) bool {
+	needsSanitize := false
+	contents.ForEach(func(_, content gjson.Result) bool {
+		isModelTurn := content.Get("role").String() == "model"
+		parts := content.Get("parts")
+		if !parts.IsArray() {
+			return true
+		}
+		parts.ForEach(func(_, part gjson.Result) bool {
+			if part.Get("functionResponse").Exists() {
+				_, needsSanitize = geminiPartThoughtSignature(part)
+				return !needsSanitize
+			}
+			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
+			}
+			replaySignature := GeminiReplaySignatureOrBypass(rawSignature, blockKind)
+			needsSanitize = !hasNormalizedGeminiPartThoughtSignature(part, replaySignature)
+			return !needsSanitize
+		})
+		return !needsSanitize
+	})
+	return needsSanitize
 }
 
 func logGeminiThoughtSignatureSanitize(contentsPath string, contentIndex, partIndex int, decision SignatureCompatibilityDecision, rawSignature string, hasSignature bool) {
@@ -106,16 +167,18 @@ func logGeminiThoughtSignatureSanitize(contentsPath string, contentIndex, partIn
 	}).Debug("gemini request: sanitized thoughtSignature before upstream")
 }
 
+var geminiPartThoughtSignaturePaths = []string{
+	"thoughtSignature",
+	"thought_signature",
+	"functionCall.thoughtSignature",
+	"functionCall.thought_signature",
+	"functionResponse.thoughtSignature",
+	"functionResponse.thought_signature",
+	"extra_content.google.thought_signature",
+}
+
 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",
-	} {
+	for _, path := range geminiPartThoughtSignaturePaths {
 		result := part.Get(path)
 		if result.Exists() {
 			return result.String(), true
@@ -124,17 +187,51 @@ func geminiPartThoughtSignature(part gjson.Result) (string, bool) {
 	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)
+func hasNormalizedGeminiPartThoughtSignature(part gjson.Result, replaySignature string) bool {
+	canonicalCount := 0
+	part.ForEach(func(key, _ gjson.Result) bool {
+		if key.String() == "thoughtSignature" {
+			canonicalCount++
+		}
+		return true
+	})
+	canonical := part.Get("thoughtSignature")
+	if canonicalCount != 1 || canonical.Type != gjson.String || canonical.String() != replaySignature {
+		return false
+	}
+	for _, path := range geminiPartThoughtSignaturePaths[1:] {
+		if part.Get(path).Exists() {
+			return false
+		}
+	}
+	return true
+}
+
+func deleteGeminiPartThoughtSignatureFields(payload []byte) []byte {
+	for _, path := range geminiPartThoughtSignaturePaths {
+		for gjson.GetBytes(payload, path).Exists() {
+			updated, errDelete := sjson.DeleteBytes(payload, path)
+			if errDelete != nil || len(updated) >= len(payload) {
+				break
+			}
+			payload = updated
+		}
 	}
 	return payload
 }
+
+func joinGeminiSignatureRawArray(items [][]byte) []byte {
+	size := len(items) + 1
+	for _, item := range items {
+		size += len(item)
+	}
+	out := make([]byte, 0, size)
+	out = append(out, '[')
+	for index, item := range items {
+		if index > 0 {
+			out = append(out, ',')
+		}
+		out = append(out, item...)
+	}
+	return append(out, ']')
+}
diff --git a/internal/signature/gemini_sanitize_test.go b/internal/signature/gemini_sanitize_test.go
index 8faf8a85..63cf456e 100644
--- a/internal/signature/gemini_sanitize_test.go
+++ b/internal/signature/gemini_sanitize_test.go
@@ -41,6 +41,8 @@ func assertSignatureDebugDoesNotLeak(t *testing.T, hook *test.Hook, forbidden st
 	}
 }
 
+var benchmarkSanitizeGeminiRequestOutput []byte
+
 func TestSanitizeGeminiRequestThoughtSignaturesPreservesGeminiSignature(t *testing.T) {
 	sig := testGemini3ThoughtSignature([]byte{0x01, 0x0c, 0x39})
 	input := []byte(`{"contents":[{"role":"model","parts":[{"functionCall":{"name":"f","args":{}},"thoughtSignature":"` + sig + `"}]}]}`)
@@ -50,6 +52,35 @@ func TestSanitizeGeminiRequestThoughtSignaturesPreservesGeminiSignature(t *testi
 	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))
 	}
+	if &out[0] != &input[0] {
+		t.Fatal("compatible canonical signature payload was copied")
+	}
+}
+
+func TestSanitizeGeminiRequestThoughtSignaturesNormalizesDuplicateCanonicalField(t *testing.T) {
+	input := []byte(`{"contents":[{"role":"model","parts":[{"functionCall":{"name":"f","args":{}},"thoughtSignature":"` + GeminiSkipThoughtSignatureValidator + `","thoughtSignature":"bad","thoughtSignature":"worse"}]}]}`)
+
+	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, out)
+	}
+	if count := strings.Count(string(out), `"thoughtSignature"`); count != 1 {
+		t.Fatalf("thoughtSignature field count = %d, want 1. Output: %s", count, out)
+	}
+}
+
+func TestSanitizeGeminiRequestThoughtSignaturesReusesUnsignedFunctionResponsePayload(t *testing.T) {
+	input := []byte(`{"contents":[{"role":"user","parts":[{"functionResponse":{"name":"f","response":{"result":"ok"}}}]}]}`)
+
+	out := SanitizeGeminiRequestThoughtSignatures(input, "contents")
+
+	if &out[0] != &input[0] {
+		t.Fatal("unsigned function response payload was copied")
+	}
+	if string(out) != string(input) {
+		t.Fatalf("payload changed:\n got: %s\nwant: %s", out, input)
+	}
 }
 
 func TestSanitizeGeminiRequestThoughtSignaturesReplacesBase64UUIDFunctionCall(t *testing.T) {
@@ -108,8 +139,46 @@ func TestSanitizeGeminiRequestThoughtSignaturesReplacesField2WrappedUUIDFunction
 	}
 }
 
+func BenchmarkSanitizeGeminiRequestThoughtSignaturesNormalizedHistory(b *testing.B) {
+	for _, turns := range []int{1, 16, 64} {
+		b.Run(fmt.Sprintf("turns_%d", turns), func(b *testing.B) {
+			input := normalizedGeminiSignatureHistory(turns, 8<<20)
+			output := SanitizeGeminiRequestThoughtSignatures(input, "contents")
+			if &output[0] != &input[0] {
+				b.Fatal("normalized payload was copied")
+			}
+			b.ReportAllocs()
+			b.SetBytes(int64(len(input)))
+			b.ResetTimer()
+
+			for b.Loop() {
+				benchmarkSanitizeGeminiRequestOutput = SanitizeGeminiRequestThoughtSignatures(input, "contents")
+			}
+		})
+	}
+}
+
+func normalizedGeminiSignatureHistory(turns, totalPayloadBytes int) []byte {
+	payload := strings.Repeat("x", totalPayloadBytes/turns)
+	var builder strings.Builder
+	builder.Grow(totalPayloadBytes + turns*256)
+	builder.WriteString(`{"contents":[`)
+	for i := 0; i < turns; i++ {
+		if i > 0 {
+			builder.WriteByte(',')
+		}
+		builder.WriteString(`{"role":"model","parts":[{"functionCall":{"name":"lookup","args":{"value":"`)
+		builder.WriteString(payload)
+		builder.WriteString(`"}},"thoughtSignature":"`)
+		builder.WriteString(GeminiSkipThoughtSignatureValidator)
+		builder.WriteString(`"}]},{"role":"user","parts":[{"functionResponse":{"name":"lookup","response":{"result":"ok"}}}]}`)
+	}
+	builder.WriteString(`]}`)
+	return []byte(builder.String())
+}
+
 func TestSanitizeGeminiRequestThoughtSignaturesRemovesFunctionResponseSignature(t *testing.T) {
-	input := []byte(`{"contents":[{"role":"user","parts":[{"functionResponse":{"name":"f","response":{"result":"ok"},"thoughtSignature":"bad"},"thoughtSignature":"bad"}]}]}`)
+	input := []byte(`{"contents":[{"role":"user","parts":[{"functionResponse":{"name":"f","response":{"result":"ok"},"thoughtSignature":"bad","thoughtSignature":"worse"},"thoughtSignature":"bad"}]}]}`)
 
 	out := SanitizeGeminiRequestThoughtSignatures(input, "contents")
 
diff --git a/internal/translator/antigravity/claude/antigravity_claude_request.go b/internal/translator/antigravity/claude/antigravity_claude_request.go
index a33aa333..1efeb3a0 100644
--- a/internal/translator/antigravity/claude/antigravity_claude_request.go
+++ b/internal/translator/antigravity/claude/antigravity_claude_request.go
@@ -587,30 +587,33 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 				}
 				clientContentJSON := antigravityClaudeContent(role, partItems)
 				if role == "model" && len(partItems) > 1 {
-					var thinkingParts []gjson.Result
-					var regularParts []gjson.Result
-					var functionCallParts []gjson.Result
+					var thinkingParts [][]byte
+					var regularParts [][]byte
+					var functionCallParts [][]byte
+					needsReorder := false
+					previousCategory := -1
 					for _, partJSON := range partItems {
 						part := gjson.ParseBytes(partJSON)
+						category := 1
 						if part.Get("thought").Bool() {
-							thinkingParts = append(thinkingParts, part)
+							category = 0
+							thinkingParts = append(thinkingParts, partJSON)
 						} else if part.Get("functionCall").Exists() {
-							functionCallParts = append(functionCallParts, part)
+							category = 2
+							functionCallParts = append(functionCallParts, partJSON)
 						} else {
-							regularParts = append(regularParts, part)
+							regularParts = append(regularParts, partJSON)
 						}
+						needsReorder = needsReorder || category < previousCategory
+						previousCategory = category
 					}
-					newParts := make([]interface{}, 0, len(partItems))
-					for _, part := range thinkingParts {
-						newParts = append(newParts, part.Value())
+					if needsReorder {
+						newParts := make([][]byte, 0, len(partItems))
+						newParts = append(newParts, thinkingParts...)
+						newParts = append(newParts, regularParts...)
+						newParts = append(newParts, functionCallParts...)
+						clientContentJSON, _ = sjson.SetRawBytes(clientContentJSON, "parts", translatorcommon.JoinRawArray(newParts))
 					}
-					for _, part := range regularParts {
-						newParts = append(newParts, part.Value())
-					}
-					for _, part := range functionCallParts {
-						newParts = append(newParts, part.Value())
-					}
-					clientContentJSON, _ = sjson.SetBytes(clientContentJSON, "parts", newParts)
 				}
 				contentItems = append(contentItems, clientContentJSON)
 			} else if contentsResult.Type == gjson.String {
@@ -642,7 +645,12 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 				inputSchema := util.CleanJSONSchemaForAntigravity(inputSchemaResult.Raw)
 				tool, _ := sjson.DeleteBytes([]byte(toolResult.Raw), "input_schema")
 				tool, _ = sjson.SetRawBytes(tool, "parametersJsonSchema", []byte(inputSchema))
-				tool, _ = sjson.SetBytes(tool, "name", util.MapSanitizedFunctionName(functionNameMap, gjson.GetBytes(tool, "name").String()))
+				nameResult := gjson.GetBytes(tool, "name")
+				originalName := nameResult.String()
+				mappedName := util.MapSanitizedFunctionName(functionNameMap, originalName)
+				if nameResult.Type != gjson.String || mappedName != originalName {
+					tool, _ = sjson.SetBytes(tool, "name", mappedName)
+				}
 				for toolKey := range gjson.ParseBytes(tool).Map() {
 					if util.InArray(allowedToolKeys, toolKey) {
 						continue
diff --git a/internal/translator/antigravity/gemini/antigravity_gemini_request.go b/internal/translator/antigravity/gemini/antigravity_gemini_request.go
index 4fc4a0d9..1824fcb2 100644
--- a/internal/translator/antigravity/gemini/antigravity_gemini_request.go
+++ b/internal/translator/antigravity/gemini/antigravity_gemini_request.go
@@ -42,7 +42,9 @@ func ConvertGeminiRequestToAntigravity(modelName string, inputRawJSON []byte, _
 	templateBytes, _ := sjson.SetRawBytes([]byte(template), "request", rawJSON)
 	templateBytes, _ = sjson.SetBytes(templateBytes, "model", modelName)
 	template = string(templateBytes)
-	template, _ = sjson.Delete(template, "request.model")
+	if gjson.Get(template, "request.model").Exists() {
+		template, _ = sjson.Delete(template, "request.model")
+	}
 
 	template, errFixCLIToolResponse := fixCLIToolResponse(template)
 	if errFixCLIToolResponse != nil {
@@ -87,44 +89,61 @@ func ConvertGeminiRequestToAntigravity(modelName string, inputRawJSON []byte, _
 	toolsResult := gjson.GetBytes(rawJSON, "request.tools")
 	if toolsResult.IsArray() {
 		seenFunctionNames := make(map[string]struct{})
+		toolsChanged := false
 		var toolItems [][]byte
 		toolsResult.ForEach(func(toolIndex, tool gjson.Result) bool {
 			toolJSON := []byte(tool.Raw)
+			toolChanged := false
 			for _, key := range []string{"functionDeclarations", "function_declarations"} {
 				declarations := tool.Get(key)
 				if !declarations.IsArray() {
 					continue
 				}
 
+				declarationsChanged := false
 				var declarationItems [][]byte
 				declarations.ForEach(func(_, declaration gjson.Result) bool {
-					mappedName := util.MapSanitizedFunctionName(functionNameMap, declaration.Get("name").String())
+					nameResult := declaration.Get("name")
+					originalName := nameResult.String()
+					mappedName := util.MapSanitizedFunctionName(functionNameMap, originalName)
 					if mappedName != "" {
 						if _, exists := seenFunctionNames[mappedName]; exists {
+							declarationsChanged = true
 							return true
 						}
 						seenFunctionNames[mappedName] = struct{}{}
 					}
 
 					declarationJSON := []byte(declaration.Raw)
-					declarationJSON, _ = sjson.SetBytes(declarationJSON, "name", mappedName)
+					if nameResult.Type != gjson.String || mappedName != originalName {
+						declarationJSON, _ = sjson.SetBytes(declarationJSON, "name", mappedName)
+						declarationsChanged = true
+					}
 					if parameters := declaration.Get("parameters"); parameters.Exists() {
 						declarationJSON, _ = sjson.SetRawBytes(declarationJSON, "parametersJsonSchema", []byte(parameters.Raw))
 						declarationJSON, _ = sjson.DeleteBytes(declarationJSON, "parameters")
+						declarationsChanged = true
 					}
 					declarationItems = append(declarationItems, declarationJSON)
 					return true
 				})
-				var errSet error
-				toolJSON, errSet = sjson.SetRawBytes(toolJSON, key, translatorcommon.JoinRawArray(declarationItems))
-				if errSet != nil {
-					log.Warnf("failed to normalize function declarations in tool %d: %v", toolIndex.Int(), errSet)
+				if declarationsChanged {
+					var errSet error
+					toolJSON, errSet = sjson.SetRawBytes(toolJSON, key, translatorcommon.JoinRawArray(declarationItems))
+					if errSet != nil {
+						log.Warnf("failed to normalize function declarations in tool %d: %v", toolIndex.Int(), errSet)
+					} else {
+						toolChanged = true
+					}
 				}
 			}
+			toolsChanged = toolsChanged || toolChanged
 			toolItems = append(toolItems, toolJSON)
 			return true
 		})
-		rawJSON, _ = sjson.SetRawBytes(rawJSON, "request.tools", translatorcommon.JoinRawArray(toolItems))
+		if toolsChanged {
+			rawJSON, _ = sjson.SetRawBytes(rawJSON, "request.tools", translatorcommon.JoinRawArray(toolItems))
+		}
 		rawJSON = removeEmptyGeminiFunctionTools(rawJSON)
 	}
 	rawJSON = rewriteGeminiFunctionNames(rawJSON, functionNameMap)
@@ -140,6 +159,11 @@ func ConvertGeminiRequestToAntigravity(modelName string, inputRawJSON []byte, _
 
 func removeEmptyGeminiFunctionTools(rawJSON []byte) []byte {
 	tools := gjson.GetBytes(rawJSON, "request.tools")
+	if tools.IsArray() && len(tools.Array()) == 0 {
+		rawJSON, _ = sjson.DeleteBytes(rawJSON, "request.tools")
+		return rawJSON
+	}
+	changed := false
 	var cleanedTools [][]byte
 	for _, tool := range tools.Array() {
 		toolJSON := []byte(tool.Raw)
@@ -147,14 +171,19 @@ func removeEmptyGeminiFunctionTools(rawJSON []byte) []byte {
 			for _, key := range []string{"functionDeclarations", "function_declarations"} {
 				if declarations := tool.Get(key); declarations.IsArray() && len(declarations.Array()) == 0 {
 					toolJSON, _ = sjson.DeleteBytes(toolJSON, key)
+					changed = true
 				}
 			}
 			if len(gjson.ParseBytes(toolJSON).Map()) == 0 {
+				changed = true
 				continue
 			}
 		}
 		cleanedTools = append(cleanedTools, toolJSON)
 	}
+	if !changed {
+		return rawJSON
+	}
 	if len(cleanedTools) == 0 {
 		rawJSON, _ = sjson.DeleteBytes(rawJSON, "request.tools")
 		return rawJSON
@@ -186,11 +215,16 @@ func rewriteGeminiFunctionNames(rawJSON []byte, functionNameMap map[string]strin
 			content.Get("parts").ForEach(func(_, part gjson.Result) bool {
 				partJSON := []byte(part.Raw)
 				for _, field := range []string{"functionCall", "functionResponse", "function_call", "function_response"} {
-					name := part.Get(field + ".name").String()
+					nameResult := part.Get(field + ".name")
+					name := nameResult.String()
 					if name == "" {
 						continue
 					}
-					partJSON, _ = sjson.SetBytes(partJSON, field+".name", util.MapSanitizedFunctionName(functionNameMap, name))
+					mappedName := util.MapSanitizedFunctionName(functionNameMap, name)
+					if nameResult.Type == gjson.String && mappedName == name {
+						continue
+					}
+					partJSON, _ = sjson.SetBytes(partJSON, field+".name", mappedName)
 					partsChanged = true
 				}
 				partItems = append(partItems, partJSON)
@@ -210,12 +244,17 @@ func rewriteGeminiFunctionNames(rawJSON []byte, functionNameMap map[string]strin
 		for contentIndex, content := range contents.Array() {
 			for partIndex, part := range content.Get("parts").Array() {
 				for _, field := range []string{"functionCall", "functionResponse", "function_call", "function_response"} {
-					name := part.Get(field + ".name").String()
+					nameResult := part.Get(field + ".name")
+					name := nameResult.String()
 					if name == "" {
 						continue
 					}
+					mappedName := util.MapSanitizedFunctionName(functionNameMap, name)
+					if nameResult.Type == gjson.String && mappedName == name {
+						continue
+					}
 					path := fmt.Sprintf("request.contents.%d.parts.%d.%s.name", contentIndex, partIndex, field)
-					rawJSON, _ = sjson.SetBytes(rawJSON, path, util.MapSanitizedFunctionName(functionNameMap, name))
+					rawJSON, _ = sjson.SetBytes(rawJSON, path, mappedName)
 				}
 			}
 		}
@@ -227,17 +266,26 @@ func rewriteGeminiFunctionNames(rawJSON []byte, functionNameMap map[string]strin
 	} {
 		allowedNames := gjson.GetBytes(rawJSON, allowedPath)
 		if allowedNames.IsArray() {
+			namesChanged := false
 			nameItems := make([][]byte, 0, 4)
 			allowedNames.ForEach(func(_, name gjson.Result) bool {
-				mappedName, _ := json.Marshal(util.MapSanitizedFunctionName(functionNameMap, name.String()))
-				nameItems = append(nameItems, mappedName)
+				mappedName := util.MapSanitizedFunctionName(functionNameMap, name.String())
+				namesChanged = namesChanged || name.Type != gjson.String || mappedName != name.String()
+				mappedNameJSON, _ := json.Marshal(mappedName)
+				nameItems = append(nameItems, mappedNameJSON)
 				return true
 			})
-			rawJSON, _ = sjson.SetRawBytes(rawJSON, allowedPath, translatorcommon.JoinRawArray(nameItems))
+			if namesChanged {
+				rawJSON, _ = sjson.SetRawBytes(rawJSON, allowedPath, translatorcommon.JoinRawArray(nameItems))
+			}
 		} else {
 			for index, name := range allowedNames.Array() {
+				mappedName := util.MapSanitizedFunctionName(functionNameMap, name.String())
+				if name.Type == gjson.String && mappedName == name.String() {
+					continue
+				}
 				path := fmt.Sprintf("%s.%d", allowedPath, index)
-				rawJSON, _ = sjson.SetBytes(rawJSON, path, util.MapSanitizedFunctionName(functionNameMap, name.String()))
+				rawJSON, _ = sjson.SetBytes(rawJSON, path, mappedName)
 			}
 		}
 	}
@@ -511,6 +559,26 @@ func fixCLIToolResponse(input string) (string, error) {
 		return input, fmt.Errorf("contents not found in input")
 	}
 
+	needsGrouping := false
+	allContentsAreObjects := true
+	contents.ForEach(func(_, content gjson.Result) bool {
+		if !content.IsObject() {
+			allContentsAreObjects = false
+			return true
+		}
+		content.Get("parts").ForEach(func(_, part gjson.Result) bool {
+			if part.Get("functionResponse").Exists() {
+				needsGrouping = true
+				return false
+			}
+			return true
+		})
+		return !needsGrouping
+	})
+	if contents.IsArray() && allContentsAreObjects && !needsGrouping {
+		return input, nil
+	}
+
 	// Initialize data structures for processing and grouping
 	contentItems := translatorcommon.NewRawArrayItems(contents.Get("#").Int())
 	var pendingGroups []*FunctionCallGroup // Groups awaiting completion with responses
diff --git a/internal/translator/antigravity/gemini/antigravity_gemini_response.go b/internal/translator/antigravity/gemini/antigravity_gemini_response.go
index 23d8f6b2..2c61913b 100644
--- a/internal/translator/antigravity/gemini/antigravity_gemini_response.go
+++ b/internal/translator/antigravity/gemini/antigravity_gemini_response.go
@@ -95,12 +95,17 @@ func restoreGeminiFunctionNames(chunk, originalRequestRawJSON []byte) []byte {
 	for candidateIndex, candidate := range candidates.Array() {
 		for partIndex, part := range candidate.Get("content.parts").Array() {
 			for _, field := range []string{"functionCall", "functionResponse", "function_call", "function_response"} {
-				name := part.Get(field + ".name").String()
+				nameResult := part.Get(field + ".name")
+				name := nameResult.String()
 				if name == "" {
 					continue
 				}
+				restoredName := util.RestoreSanitizedToolName(nameMap, name)
+				if nameResult.Type == gjson.String && restoredName == name {
+					continue
+				}
 				path := fmt.Sprintf("candidates.%d.content.parts.%d.%s.name", candidateIndex, partIndex, field)
-				chunk, _ = sjson.SetBytes(chunk, path, util.RestoreSanitizedToolName(nameMap, name))
+				chunk, _ = sjson.SetBytes(chunk, path, restoredName)
 			}
 		}
 	}
diff --git a/internal/translator/antigravity/gemini/noop_optimization_test.go b/internal/translator/antigravity/gemini/noop_optimization_test.go
new file mode 100644
index 00000000..16ea1317
--- /dev/null
+++ b/internal/translator/antigravity/gemini/noop_optimization_test.go
@@ -0,0 +1,74 @@
+package gemini
+
+import (
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestRewriteGeminiFunctionNamesReusesNormalizedPayload(t *testing.T) {
+	input := []byte(`{"request":{"contents":[{"role":"model","parts":[{"functionCall":{"name":"lookup","args":{}}}]},{"role":"user","parts":[{"functionResponse":{"name":"lookup","response":{"result":"ok"}}}]}],"toolConfig":{"functionCallingConfig":{"allowedFunctionNames":["lookup"]}}}}`)
+
+	output := rewriteGeminiFunctionNames(input, nil)
+
+	if &output[0] != &input[0] {
+		t.Fatal("normalized function names caused a payload copy")
+	}
+}
+
+func TestRemoveEmptyGeminiFunctionToolsReusesNormalizedPayload(t *testing.T) {
+	input := []byte(`{"request":{"tools":[{"functionDeclarations":[{"name":"lookup"}]}]}}`)
+
+	output := removeEmptyGeminiFunctionTools(input)
+
+	if &output[0] != &input[0] {
+		t.Fatal("non-empty tools caused a payload copy")
+	}
+}
+
+func TestRemoveEmptyGeminiFunctionToolsDeletesEmptyArray(t *testing.T) {
+	input := []byte(`{"request":{"tools":[]}}`)
+
+	output := removeEmptyGeminiFunctionTools(input)
+
+	if gjson.GetBytes(output, "request.tools").Exists() {
+		t.Fatalf("empty tools should be removed: %s", output)
+	}
+}
+
+func TestRewriteGeminiFunctionNamesNormalizesNonStringNames(t *testing.T) {
+	input := []byte(`{"request":{"contents":[{"role":"model","parts":[{"functionCall":{"name":true,"args":{}}}]}],"toolConfig":{"functionCallingConfig":{"allowedFunctionNames":[true]}}}}`)
+
+	output := rewriteGeminiFunctionNames(input, nil)
+
+	if name := gjson.GetBytes(output, "request.contents.0.parts.0.functionCall.name"); name.Type != gjson.String || name.String() != "true" {
+		t.Fatalf("functionCall.name = %s, want string true", name.Raw)
+	}
+	if name := gjson.GetBytes(output, "request.toolConfig.functionCallingConfig.allowedFunctionNames.0"); name.Type != gjson.String || name.String() != "true" {
+		t.Fatalf("allowedFunctionNames.0 = %s, want string true", name.Raw)
+	}
+}
+
+func TestFixCLIToolResponseReusesHistoryWithoutFunctionResponses(t *testing.T) {
+	input := `{"request":{"contents":[{"role":"user","parts":[{"text":"hello"}]},{"role":"model","parts":[{"text":"world"}]}]}}`
+
+	output, errFix := fixCLIToolResponse(input)
+	if errFix != nil {
+		t.Fatalf("fixCLIToolResponse returned an error: %v", errFix)
+	}
+	if output != input {
+		t.Fatalf("history changed:\n got: %s\nwant: %s", output, input)
+	}
+}
+
+func TestFixCLIToolResponsePreservesObjectNormalization(t *testing.T) {
+	input := `{"request":{"contents":{"first":{"role":"user","parts":[{"text":"hello"}]}}}}`
+
+	output, errFix := fixCLIToolResponse(input)
+	if errFix != nil {
+		t.Fatalf("fixCLIToolResponse returned an error: %v", errFix)
+	}
+	if !gjson.Get(output, "request.contents").IsArray() {
+		t.Fatalf("contents should be normalized to an array: %s", output)
+	}
+}
diff --git a/internal/translator/antigravity/interactions/interactions_antigravity_request.go b/internal/translator/antigravity/interactions/interactions_antigravity_request.go
index 5fc445a4..123b42dc 100644
--- a/internal/translator/antigravity/interactions/interactions_antigravity_request.go
+++ b/internal/translator/antigravity/interactions/interactions_antigravity_request.go
@@ -53,11 +53,16 @@ func rewriteInteractionsFunctionNames(out []byte, functionNameMap map[string]str
 			content.Get("parts").ForEach(func(_, part gjson.Result) bool {
 				partJSON := []byte(part.Raw)
 				for _, field := range []string{"functionCall", "functionResponse"} {
-					name := part.Get(field + ".name").String()
+					nameResult := part.Get(field + ".name")
+					name := nameResult.String()
 					if name == "" {
 						continue
 					}
-					partJSON, _ = sjson.SetBytes(partJSON, field+".name", util.MapSanitizedFunctionName(functionNameMap, name))
+					mappedName := util.MapSanitizedFunctionName(functionNameMap, name)
+					if nameResult.Type == gjson.String && mappedName == name {
+						continue
+					}
+					partJSON, _ = sjson.SetBytes(partJSON, field+".name", mappedName)
 					partsChanged = true
 				}
 				partItems = append(partItems, partJSON)
@@ -77,12 +82,17 @@ func rewriteInteractionsFunctionNames(out []byte, functionNameMap map[string]str
 		for contentIndex, content := range contents.Array() {
 			for partIndex, part := range content.Get("parts").Array() {
 				for _, field := range []string{"functionCall", "functionResponse"} {
-					name := part.Get(field + ".name").String()
+					nameResult := part.Get(field + ".name")
+					name := nameResult.String()
 					if name == "" {
 						continue
 					}
+					mappedName := util.MapSanitizedFunctionName(functionNameMap, name)
+					if nameResult.Type == gjson.String && mappedName == name {
+						continue
+					}
 					path := fmt.Sprintf("request.contents.%d.parts.%d.%s.name", contentIndex, partIndex, field)
-					out, _ = sjson.SetBytes(out, path, util.MapSanitizedFunctionName(functionNameMap, name))
+					out, _ = sjson.SetBytes(out, path, mappedName)
 				}
 			}
 		}
@@ -91,17 +101,26 @@ func rewriteInteractionsFunctionNames(out []byte, functionNameMap map[string]str
 	allowedPath := "request.toolConfig.functionCallingConfig.allowedFunctionNames"
 	allowedNames := gjson.GetBytes(out, allowedPath)
 	if allowedNames.IsArray() {
+		namesChanged := false
 		nameItems := make([][]byte, 0, 4)
 		allowedNames.ForEach(func(_, name gjson.Result) bool {
-			mappedName, _ := json.Marshal(util.MapSanitizedFunctionName(functionNameMap, name.String()))
-			nameItems = append(nameItems, mappedName)
+			mappedName := util.MapSanitizedFunctionName(functionNameMap, name.String())
+			namesChanged = namesChanged || name.Type != gjson.String || mappedName != name.String()
+			mappedNameJSON, _ := json.Marshal(mappedName)
+			nameItems = append(nameItems, mappedNameJSON)
 			return true
 		})
-		out, _ = sjson.SetRawBytes(out, allowedPath, translatorcommon.JoinRawArray(nameItems))
+		if namesChanged {
+			out, _ = sjson.SetRawBytes(out, allowedPath, translatorcommon.JoinRawArray(nameItems))
+		}
 	} else {
 		for index, name := range allowedNames.Array() {
+			mappedName := util.MapSanitizedFunctionName(functionNameMap, name.String())
+			if name.Type == gjson.String && mappedName == name.String() {
+				continue
+			}
 			path := fmt.Sprintf("%s.%d", allowedPath, index)
-			out, _ = sjson.SetBytes(out, path, util.MapSanitizedFunctionName(functionNameMap, name.String()))
+			out, _ = sjson.SetBytes(out, path, mappedName)
 		}
 	}
 	return out
@@ -572,7 +591,6 @@ func antigravityFunctionDeclarationJSON(decl gjson.Result, functionNameMap map[s
 	if responseSchema := fn.Get("responseJsonSchema"); responseSchema.Exists() {
 		out, _ = sjson.SetRawBytes(out, "responseJsonSchema", []byte(responseSchema.Raw))
 	}
-	out, _ = sjson.DeleteBytes(out, "strict")
 	return out
 }
 
diff --git a/internal/translator/antigravity/interactions/interactions_antigravity_response.go b/internal/translator/antigravity/interactions/interactions_antigravity_response.go
index f7cafd10..4b46c060 100644
--- a/internal/translator/antigravity/interactions/interactions_antigravity_response.go
+++ b/internal/translator/antigravity/interactions/interactions_antigravity_response.go
@@ -143,12 +143,17 @@ func restoreInteractionsFunctionNames(root gjson.Result, nameMap map[string]stri
 	for candidateIndex, candidate := range candidates.Array() {
 		for partIndex, part := range candidate.Get("content.parts").Array() {
 			for _, field := range []string{"functionCall", "functionResponse"} {
-				name := part.Get(field + ".name").String()
+				nameResult := part.Get(field + ".name")
+				name := nameResult.String()
 				if name == "" {
 					continue
 				}
+				restoredName := util.RestoreSanitizedToolName(nameMap, name)
+				if nameResult.Type == gjson.String && restoredName == name {
+					continue
+				}
 				path := fmt.Sprintf("candidates.%d.content.parts.%d.%s.name", candidateIndex, partIndex, field)
-				raw, _ = sjson.SetBytes(raw, path, util.RestoreSanitizedToolName(nameMap, name))
+				raw, _ = sjson.SetBytes(raw, path, restoredName)
 			}
 		}
 	}
diff --git a/internal/translator/antigravity/interactions/noop_optimization_test.go b/internal/translator/antigravity/interactions/noop_optimization_test.go
new file mode 100644
index 00000000..976f1d17
--- /dev/null
+++ b/internal/translator/antigravity/interactions/noop_optimization_test.go
@@ -0,0 +1,30 @@
+package interactions
+
+import (
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestRewriteInteractionsFunctionNamesReusesNormalizedPayload(t *testing.T) {
+	input := []byte(`{"request":{"contents":[{"role":"model","parts":[{"functionCall":{"name":"lookup","args":{}}}]},{"role":"user","parts":[{"functionResponse":{"name":"lookup","response":{"result":"ok"}}}]}],"toolConfig":{"functionCallingConfig":{"allowedFunctionNames":["lookup"]}}}}`)
+
+	output := rewriteInteractionsFunctionNames(input, nil)
+
+	if &output[0] != &input[0] {
+		t.Fatal("normalized function names caused a payload copy")
+	}
+}
+
+func TestRewriteInteractionsFunctionNamesNormalizesNonStringNames(t *testing.T) {
+	input := []byte(`{"request":{"contents":[{"role":"model","parts":[{"functionCall":{"name":true,"args":{}}}]}],"toolConfig":{"functionCallingConfig":{"allowedFunctionNames":[true]}}}}`)
+
+	output := rewriteInteractionsFunctionNames(input, nil)
+
+	if name := gjson.GetBytes(output, "request.contents.0.parts.0.functionCall.name"); name.Type != gjson.String || name.String() != "true" {
+		t.Fatalf("functionCall.name = %s, want string true", name.Raw)
+	}
+	if name := gjson.GetBytes(output, "request.toolConfig.functionCallingConfig.allowedFunctionNames.0"); name.Type != gjson.String || name.String() != "true" {
+		t.Fatalf("allowedFunctionNames.0 = %s, want string true", name.Raw)
+	}
+}
diff --git a/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go b/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go
index ad005316..98cc95c7 100644
--- a/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go
+++ b/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go
@@ -349,9 +349,16 @@ func ConvertOpenAIRequestToAntigravity(modelName string, inputRawJSON []byte, _
 						fnRaw = string(fnRawBytes)
 					}
 					fnRawBytes := []byte(fnRaw)
-					fnRawBytes, _ = sjson.SetBytes(fnRawBytes, "name", util.MapSanitizedFunctionName(functionNameMap, fn.Get("name").String()))
-					fnRaw, _ = sjson.Delete(string(fnRawBytes), "strict")
-					functionDeclarations = append(functionDeclarations, []byte(fnRaw))
+					nameResult := fn.Get("name")
+					originalName := nameResult.String()
+					mappedName := util.MapSanitizedFunctionName(functionNameMap, originalName)
+					if nameResult.Type != gjson.String || mappedName != originalName {
+						fnRawBytes, _ = sjson.SetBytes(fnRawBytes, "name", mappedName)
+					}
+					if gjson.GetBytes(fnRawBytes, "strict").Exists() {
+						fnRawBytes, _ = sjson.DeleteBytes(fnRawBytes, "strict")
+					}
+					functionDeclarations = append(functionDeclarations, fnRawBytes)
 				}
 			}
 			if gs := t.Get("google_search"); gs.Exists() {
@@ -496,16 +503,16 @@ func applyOpenAIThinkingCompatibilityToAntigravity(out []byte, rawJSON []byte, m
 		"reasoning.include_thoughts",
 	} {
 		if value := gjson.GetBytes(rawJSON, path); value.Exists() {
-			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.includeThoughts", value.Bool())
+			out = setAntigravityOpenAIBoolIfDifferent(out, "request.generationConfig.thinkingConfig.includeThoughts", value.Bool())
 		}
 	}
 
 	if exclude := gjson.GetBytes(rawJSON, "reasoning.exclude"); exclude.Exists() {
-		out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.includeThoughts", !exclude.Bool())
+		out = setAntigravityOpenAIBoolIfDifferent(out, "request.generationConfig.thinkingConfig.includeThoughts", !exclude.Bool())
 	}
 
 	if !gjson.GetBytes(out, "request.generationConfig.thinkingConfig.includeThoughts").Exists() && antigravityOpenAIDefaultIncludeThoughts(modelName) {
-		out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.includeThoughts", true)
+		out = setAntigravityOpenAIBoolIfDifferent(out, "request.generationConfig.thinkingConfig.includeThoughts", true)
 	}
 
 	return normalizeAntigravityOpenAIThinkingConfig(out)
@@ -517,22 +524,22 @@ func normalizeAntigravityOpenAIThinkingConfig(out []byte) []byte {
 		"request.generationConfig.thinkingConfig",
 	} {
 		if includeThoughts := gjson.GetBytes(out, prefix+".includeThoughts"); includeThoughts.Exists() {
-			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.includeThoughts", includeThoughts.Bool())
+			out = setAntigravityOpenAIBoolIfDifferent(out, "request.generationConfig.thinkingConfig.includeThoughts", includeThoughts.Bool())
 		}
 		if includeThoughts := gjson.GetBytes(out, prefix+".include_thoughts"); includeThoughts.Exists() {
-			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.includeThoughts", includeThoughts.Bool())
+			out = setAntigravityOpenAIBoolIfDifferent(out, "request.generationConfig.thinkingConfig.includeThoughts", includeThoughts.Bool())
 		}
 		if thinkingLevel := gjson.GetBytes(out, prefix+".thinkingLevel"); thinkingLevel.Exists() {
-			out, _ = sjson.SetRawBytes(out, "request.generationConfig.thinkingConfig.thinkingLevel", []byte(thinkingLevel.Raw))
+			out = setAntigravityOpenAIRawIfDifferent(out, "request.generationConfig.thinkingConfig.thinkingLevel", thinkingLevel)
 		}
 		if thinkingLevel := gjson.GetBytes(out, prefix+".thinking_level"); thinkingLevel.Exists() {
-			out, _ = sjson.SetRawBytes(out, "request.generationConfig.thinkingConfig.thinkingLevel", []byte(thinkingLevel.Raw))
+			out = setAntigravityOpenAIRawIfDifferent(out, "request.generationConfig.thinkingConfig.thinkingLevel", thinkingLevel)
 		}
 		if thinkingBudget := gjson.GetBytes(out, prefix+".thinkingBudget"); thinkingBudget.Exists() {
-			out, _ = sjson.SetRawBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", []byte(thinkingBudget.Raw))
+			out = setAntigravityOpenAIRawIfDifferent(out, "request.generationConfig.thinkingConfig.thinkingBudget", thinkingBudget)
 		}
 		if thinkingBudget := gjson.GetBytes(out, prefix+".thinking_budget"); thinkingBudget.Exists() {
-			out, _ = sjson.SetRawBytes(out, "request.generationConfig.thinkingConfig.thinkingBudget", []byte(thinkingBudget.Raw))
+			out = setAntigravityOpenAIRawIfDifferent(out, "request.generationConfig.thinkingConfig.thinkingBudget", thinkingBudget)
 		}
 	}
 
@@ -541,7 +548,7 @@ func normalizeAntigravityOpenAIThinkingConfig(out []byte) []byte {
 		"request.generationConfig.include_thoughts",
 	} {
 		if includeThoughts := gjson.GetBytes(out, path); includeThoughts.Exists() {
-			out, _ = sjson.SetBytes(out, "request.generationConfig.thinkingConfig.includeThoughts", includeThoughts.Bool())
+			out = setAntigravityOpenAIBoolIfDifferent(out, "request.generationConfig.thinkingConfig.includeThoughts", includeThoughts.Bool())
 		}
 	}
 
@@ -553,12 +560,38 @@ func normalizeAntigravityOpenAIThinkingConfig(out []byte) []byte {
 		"request.generationConfig.includeThoughts",
 		"request.generationConfig.include_thoughts",
 	} {
-		out, _ = sjson.DeleteBytes(out, path)
+		if gjson.GetBytes(out, path).Exists() {
+			out, _ = sjson.DeleteBytes(out, path)
+		}
 	}
 
 	return out
 }
 
+func setAntigravityOpenAIBoolIfDifferent(out []byte, path string, value bool) []byte {
+	current := gjson.GetBytes(out, path)
+	if value && current.Type == gjson.True || !value && current.Type == gjson.False {
+		return out
+	}
+	updated, errSet := sjson.SetBytes(out, path, value)
+	if errSet != nil {
+		return out
+	}
+	return updated
+}
+
+func setAntigravityOpenAIRawIfDifferent(out []byte, path string, value gjson.Result) []byte {
+	current := gjson.GetBytes(out, path)
+	if current.Exists() && current.Raw == value.Raw {
+		return out
+	}
+	updated, errSet := sjson.SetRawBytes(out, path, []byte(value.Raw))
+	if errSet != nil {
+		return out
+	}
+	return updated
+}
+
 func antigravityOpenAIDefaultIncludeThoughts(modelName string) bool {
 	modelName = strings.ToLower(modelName)
 	return strings.Contains(modelName, "gemini-3")
diff --git a/internal/translator/antigravity/openai/chat-completions/antigravity_openai_response.go b/internal/translator/antigravity/openai/chat-completions/antigravity_openai_response.go
index bc3e535c..60fe4895 100644
--- a/internal/translator/antigravity/openai/chat-completions/antigravity_openai_response.go
+++ b/internal/translator/antigravity/openai/chat-completions/antigravity_openai_response.go
@@ -256,12 +256,17 @@ func restoreAntigravityOpenAIFunctionNames(rawJSON, originalRequestRawJSON []byt
 	for candidateIndex, candidate := range candidates.Array() {
 		for partIndex, part := range candidate.Get("content.parts").Array() {
 			for _, field := range []string{"functionCall", "functionResponse"} {
-				name := part.Get(field + ".name").String()
+				nameResult := part.Get(field + ".name")
+				name := nameResult.String()
 				if name == "" {
 					continue
 				}
+				restoredName := util.RestoreSanitizedToolName(nameMap, name)
+				if nameResult.Type == gjson.String && restoredName == name {
+					continue
+				}
 				path := fmt.Sprintf("candidates.%d.content.parts.%d.%s.name", candidateIndex, partIndex, field)
-				rawJSON, _ = sjson.SetBytes(rawJSON, path, util.RestoreSanitizedToolName(nameMap, name))
+				rawJSON, _ = sjson.SetBytes(rawJSON, path, restoredName)
 			}
 		}
 	}
diff --git a/internal/translator/antigravity/openai/chat-completions/noop_optimization_test.go b/internal/translator/antigravity/openai/chat-completions/noop_optimization_test.go
new file mode 100644
index 00000000..7024e502
--- /dev/null
+++ b/internal/translator/antigravity/openai/chat-completions/noop_optimization_test.go
@@ -0,0 +1,13 @@
+package chat_completions
+
+import "testing"
+
+func TestNormalizeAntigravityOpenAIThinkingConfigReusesCanonicalConfig(t *testing.T) {
+	input := []byte(`{"request":{"generationConfig":{"thinkingConfig":{"includeThoughts":true,"thinkingLevel":"high","thinkingBudget":8192}}}}`)
+
+	output := normalizeAntigravityOpenAIThinkingConfig(input)
+
+	if &output[0] != &input[0] {
+		t.Fatal("canonical thinking config caused a payload copy")
+	}
+}
diff --git a/internal/translator/claude/gemini/claude_gemini_request.go b/internal/translator/claude/gemini/claude_gemini_request.go
index 9ed4d620..ccbaa9d0 100644
--- a/internal/translator/claude/gemini/claude_gemini_request.go
+++ b/internal/translator/claude/gemini/claude_gemini_request.go
@@ -377,16 +377,10 @@ func ConvertGeminiRequestToClaude(modelName string, inputRawJSON []byte, stream
 						anthropicTool, _ = sjson.SetBytes(anthropicTool, "description", desc.String())
 					}
 					if params := funcDecl.Get("parameters"); params.Exists() {
-						// Clean up the parameters schema for Claude Code compatibility
-						cleaned := []byte(params.Raw)
-						cleaned, _ = sjson.SetBytes(cleaned, "additionalProperties", false)
-						cleaned, _ = sjson.SetBytes(cleaned, "$schema", "http://json-schema.org/draft-07/schema#")
+						cleaned := normalizeClaudeToolSchema(params)
 						anthropicTool, _ = sjson.SetRawBytes(anthropicTool, "input_schema", cleaned)
 					} else if params = funcDecl.Get("parametersJsonSchema"); params.Exists() {
-						// Clean up the parameters schema for Claude Code compatibility
-						cleaned := []byte(params.Raw)
-						cleaned, _ = sjson.SetBytes(cleaned, "additionalProperties", false)
-						cleaned, _ = sjson.SetBytes(cleaned, "$schema", "http://json-schema.org/draft-07/schema#")
+						cleaned := normalizeClaudeToolSchema(params)
 						anthropicTool, _ = sjson.SetRawBytes(anthropicTool, "input_schema", cleaned)
 					}
 
@@ -416,12 +410,29 @@ func ConvertGeminiRequestToClaude(modelName string, inputRawJSON []byte, stream
 	return out
 }
 
+func normalizeClaudeToolSchema(parameters gjson.Result) []byte {
+	cleaned := []byte(parameters.Raw)
+	if parameters.Get("additionalProperties").Type != gjson.False {
+		cleaned, _ = sjson.SetBytes(cleaned, "additionalProperties", false)
+	}
+	const schema = "http://json-schema.org/draft-07/schema#"
+	currentSchema := parameters.Get("$schema")
+	if currentSchema.Type != gjson.String || currentSchema.String() != schema {
+		cleaned, _ = sjson.SetBytes(cleaned, "$schema", schema)
+	}
+	return cleaned
+}
+
 func lowercaseClaudeToolSchemaTypes(tool []byte) []byte {
 	var pathsToLower []string
 	util.Walk(gjson.ParseBytes(tool), "", "type", &pathsToLower)
 	for _, path := range pathsToLower {
 		typeValue := gjson.GetBytes(tool, path)
-		tool, _ = sjson.SetBytes(tool, path, strings.ToLower(typeValue.String()))
+		normalizedType := strings.ToLower(typeValue.String())
+		if typeValue.Type == gjson.String && normalizedType == typeValue.String() {
+			continue
+		}
+		tool, _ = sjson.SetBytes(tool, path, normalizedType)
 	}
 	return tool
 }
diff --git a/internal/translator/claude/gemini/noop_optimization_test.go b/internal/translator/claude/gemini/noop_optimization_test.go
new file mode 100644
index 00000000..f6e2e8bd
--- /dev/null
+++ b/internal/translator/claude/gemini/noop_optimization_test.go
@@ -0,0 +1,63 @@
+package gemini
+
+import (
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestNormalizeClaudeToolSchemaPreservesCanonicalSchema(t *testing.T) {
+	input := []byte(`{"type":"object","properties":{"value":{"type":"string"}},"additionalProperties":false,"$schema":"http://json-schema.org/draft-07/schema#"}`)
+
+	output := normalizeClaudeToolSchema(gjson.ParseBytes(input))
+
+	if string(output) != string(input) {
+		t.Fatalf("canonical schema changed:\n got: %s\nwant: %s", output, input)
+	}
+}
+
+func TestNormalizeClaudeToolSchemaCorrectsWrongTypes(t *testing.T) {
+	input := []byte(`{"type":"object","additionalProperties":"false","$schema":123}`)
+
+	output := normalizeClaudeToolSchema(gjson.ParseBytes(input))
+
+	if additionalProperties := gjson.GetBytes(output, "additionalProperties"); additionalProperties.Type != gjson.False {
+		t.Fatalf("additionalProperties = %s, want false", additionalProperties.Raw)
+	}
+	if schema := gjson.GetBytes(output, "$schema"); schema.Type != gjson.String || schema.String() != "http://json-schema.org/draft-07/schema#" {
+		t.Fatalf("$schema = %s, want canonical string", schema.Raw)
+	}
+}
+
+func TestLowercaseClaudeToolSchemaTypesReusesLowercaseSchema(t *testing.T) {
+	input := []byte(`{"name":"lookup","input_schema":{"type":"object","properties":{"value":{"type":"string"}}}}`)
+
+	output := lowercaseClaudeToolSchemaTypes(input)
+
+	if &output[0] != &input[0] {
+		t.Fatal("lowercase schema types caused a payload copy")
+	}
+}
+
+func TestLowercaseClaudeToolSchemaTypesNormalizesNonStringType(t *testing.T) {
+	input := []byte(`{"input_schema":{"type":123}}`)
+
+	output := lowercaseClaudeToolSchemaTypes(input)
+
+	if got := gjson.GetBytes(output, "input_schema.type"); got.Type != gjson.String || got.String() != "123" {
+		t.Fatalf("input_schema.type = %s, want string 123", got.Raw)
+	}
+}
+
+func TestLowercaseClaudeToolSchemaTypesNormalizesUppercaseTypes(t *testing.T) {
+	input := []byte(`{"input_schema":{"type":"OBJECT","properties":{"value":{"type":"STRING"}}}}`)
+
+	output := lowercaseClaudeToolSchemaTypes(input)
+
+	if got := gjson.GetBytes(output, "input_schema.type").String(); got != "object" {
+		t.Fatalf("input_schema.type = %q, want object", got)
+	}
+	if got := gjson.GetBytes(output, "input_schema.properties.value.type").String(); got != "string" {
+		t.Fatalf("nested type = %q, want string", got)
+	}
+}
diff --git a/internal/translator/claude/openai/chat-completions/claude_openai_response.go b/internal/translator/claude/openai/chat-completions/claude_openai_response.go
index 99c75238..002d3166 100644
--- a/internal/translator/claude/openai/chat-completions/claude_openai_response.go
+++ b/internal/translator/claude/openai/chat-completions/claude_openai_response.go
@@ -459,11 +459,11 @@ func ConvertClaudeResponseToOpenAINonStream(_ context.Context, _ string, origina
 		}
 		if toolCallsCount > 0 {
 			out, _ = sjson.SetBytes(out, "choices.0.finish_reason", "tool_calls")
-		} else {
-			out, _ = sjson.SetBytes(out, "choices.0.finish_reason", mapAnthropicStopReasonToOpenAI(stopReason))
+		} else if finishReason := mapAnthropicStopReasonToOpenAI(stopReason); finishReason != "stop" {
+			out, _ = sjson.SetBytes(out, "choices.0.finish_reason", finishReason)
 		}
-	} else {
-		out, _ = sjson.SetBytes(out, "choices.0.finish_reason", mapAnthropicStopReasonToOpenAI(stopReason))
+	} else if finishReason := mapAnthropicStopReasonToOpenAI(stopReason); finishReason != "stop" {
+		out, _ = sjson.SetBytes(out, "choices.0.finish_reason", finishReason)
 	}
 
 	return out
diff --git a/internal/translator/claude/openai/chat-completions/noop_optimization_test.go b/internal/translator/claude/openai/chat-completions/noop_optimization_test.go
new file mode 100644
index 00000000..1a917ca3
--- /dev/null
+++ b/internal/translator/claude/openai/chat-completions/noop_optimization_test.go
@@ -0,0 +1,30 @@
+package chat_completions
+
+import (
+	"context"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestConvertClaudeResponseToOpenAINonStreamFinishReasons(t *testing.T) {
+	tests := []struct {
+		name       string
+		stopReason string
+		want       string
+	}{
+		{name: "missing", want: "stop"},
+		{name: "end_turn", stopReason: "end_turn", want: "stop"},
+		{name: "stop_sequence", stopReason: "stop_sequence", want: "stop"},
+		{name: "max_tokens", stopReason: "max_tokens", want: "length"},
+	}
+	for _, testCase := range tests {
+		t.Run(testCase.name, func(t *testing.T) {
+			raw := []byte(`data: {"type":"message_delta","delta":{"stop_reason":"` + testCase.stopReason + `"}}`)
+			output := ConvertClaudeResponseToOpenAINonStream(context.Background(), "", nil, nil, raw, nil)
+			if got := gjson.GetBytes(output, "choices.0.finish_reason").String(); got != testCase.want {
+				t.Fatalf("finish_reason = %q, want %q", got, testCase.want)
+			}
+		})
+	}
+}
diff --git a/internal/translator/claude/openai/responses/claude_openai-responses_response.go b/internal/translator/claude/openai/responses/claude_openai-responses_response.go
index e31a856a..671f98d0 100644
--- a/internal/translator/claude/openai/responses/claude_openai-responses_response.go
+++ b/internal/translator/claude/openai/responses/claude_openai-responses_response.go
@@ -900,10 +900,18 @@ func ConvertClaudeResponseToOpenAIResponsesNonStream(_ context.Context, _ string
 
 	// Usage
 	inputTokens, outputTokens, totalTokens, cachedTokens := usageTokens.OpenAIResponsesUsage()
-	out, _ = sjson.SetBytes(out, "usage.input_tokens", inputTokens)
-	out, _ = sjson.SetBytes(out, "usage.input_tokens_details.cached_tokens", cachedTokens)
-	out, _ = sjson.SetBytes(out, "usage.output_tokens", outputTokens)
-	out, _ = sjson.SetBytes(out, "usage.total_tokens", totalTokens)
+	if inputTokens != 0 {
+		out, _ = sjson.SetBytes(out, "usage.input_tokens", inputTokens)
+	}
+	if cachedTokens != 0 {
+		out, _ = sjson.SetBytes(out, "usage.input_tokens_details.cached_tokens", cachedTokens)
+	}
+	if outputTokens != 0 {
+		out, _ = sjson.SetBytes(out, "usage.output_tokens", outputTokens)
+	}
+	if totalTokens != 0 {
+		out, _ = sjson.SetBytes(out, "usage.total_tokens", totalTokens)
+	}
 	if reasoningBuf.Len() > 0 {
 		// Rough estimate similar to chat completions
 		reasoningTokens := int64(len(reasoningBuf.String()) / 4)
diff --git a/internal/translator/claude/openai/responses/noop_optimization_test.go b/internal/translator/claude/openai/responses/noop_optimization_test.go
new file mode 100644
index 00000000..81ebb505
--- /dev/null
+++ b/internal/translator/claude/openai/responses/noop_optimization_test.go
@@ -0,0 +1,21 @@
+package responses
+
+import (
+	"context"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestConvertClaudeResponseToOpenAIResponsesNonStreamKeepsZeroUsageDefaults(t *testing.T) {
+	input := []byte(`data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"hello"}}`)
+
+	output := ConvertClaudeResponseToOpenAIResponsesNonStream(context.Background(), "", nil, nil, input, nil)
+
+	for _, path := range []string{"usage.input_tokens", "usage.input_tokens_details.cached_tokens", "usage.output_tokens", "usage.total_tokens"} {
+		value := gjson.GetBytes(output, path)
+		if !value.Exists() || value.Int() != 0 {
+			t.Fatalf("%s = %s, want zero", path, value.Raw)
+		}
+	}
+}
diff --git a/internal/translator/codex/claude/codex_claude_request.go b/internal/translator/codex/claude/codex_claude_request.go
index 888bfa45..3a27e850 100644
--- a/internal/translator/codex/claude/codex_claude_request.go
+++ b/internal/translator/codex/claude/codex_claude_request.go
@@ -273,23 +273,31 @@ func ConvertClaudeRequestToCodex(modelName string, inputRawJSON []byte, _ bool)
 				continue
 			}
 			tool := []byte(toolResult.Raw)
-			tool, _ = sjson.SetBytes(tool, "type", "function")
+			if toolResult.Get("type").Type != gjson.String || toolResult.Get("type").String() != "function" {
+				tool, _ = sjson.SetBytes(tool, "type", "function")
+			}
 			// Apply shortened name if needed
 			if v := toolResult.Get("name"); v.Exists() {
-				name := v.String()
+				originalName := v.String()
+				name := originalName
 				if short, ok := toolNameMap[name]; ok {
 					name = short
 				} else {
 					name = shortenNameIfNeeded(name)
 				}
-				tool, _ = sjson.SetBytes(tool, "name", name)
+				if v.Type != gjson.String || name != originalName {
+					tool, _ = sjson.SetBytes(tool, "name", name)
+				}
 			}
 			tool, _ = sjson.SetRawBytes(tool, "parameters", []byte(normalizeToolParameters(toolResult.Get("input_schema").Raw)))
-			tool, _ = sjson.DeleteBytes(tool, "input_schema")
-			tool, _ = sjson.DeleteBytes(tool, "parameters.$schema")
-			tool, _ = sjson.DeleteBytes(tool, "cache_control")
-			tool, _ = sjson.DeleteBytes(tool, "defer_loading")
-			tool, _ = sjson.SetBytes(tool, "strict", false)
+			for _, path := range []string{"input_schema", "parameters.$schema", "cache_control", "defer_loading"} {
+				if gjson.GetBytes(tool, path).Exists() {
+					tool, _ = sjson.DeleteBytes(tool, path)
+				}
+			}
+			if gjson.GetBytes(tool, "strict").Type != gjson.False {
+				tool, _ = sjson.SetBytes(tool, "strict", false)
+			}
 			toolItems = append(toolItems, tool)
 		}
 	}
diff --git a/internal/translator/codex/claude/noop_optimization_test.go b/internal/translator/codex/claude/noop_optimization_test.go
new file mode 100644
index 00000000..49754946
--- /dev/null
+++ b/internal/translator/codex/claude/noop_optimization_test.go
@@ -0,0 +1,18 @@
+package claude
+
+import (
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestConvertClaudeRequestToCodexNormalizesNonStringToolName(t *testing.T) {
+	input := []byte(`{"messages":[],"tools":[{"name":123,"input_schema":{"type":"object"}}]}`)
+
+	output := ConvertClaudeRequestToCodex("gpt-test", input, false)
+
+	name := gjson.GetBytes(output, "tools.0.name")
+	if name.Type != gjson.String || name.String() != "123" {
+		t.Fatalf("tools.0.name = %s, want string 123", name.Raw)
+	}
+}
diff --git a/internal/translator/codex/gemini/codex_gemini_request.go b/internal/translator/codex/gemini/codex_gemini_request.go
index a53a067e..e61dc975 100644
--- a/internal/translator/codex/gemini/codex_gemini_request.go
+++ b/internal/translator/codex/gemini/codex_gemini_request.go
@@ -262,16 +262,10 @@ func ConvertGeminiRequestToCodex(modelName string, inputRawJSON []byte, _ bool)
 					tool, _ = sjson.SetBytes(tool, "description", v.String())
 				}
 				if prm := fn.Get("parameters"); prm.Exists() {
-					// Remove optional $schema field if present
-					cleaned := []byte(prm.Raw)
-					cleaned, _ = sjson.DeleteBytes(cleaned, "$schema")
-					cleaned, _ = sjson.SetBytes(cleaned, "additionalProperties", false)
+					cleaned := cleanGeminiCodexToolParameters(prm)
 					tool, _ = sjson.SetRawBytes(tool, "parameters", cleaned)
 				} else if prm = fn.Get("parametersJsonSchema"); prm.Exists() {
-					// Remove optional $schema field if present
-					cleaned := []byte(prm.Raw)
-					cleaned, _ = sjson.DeleteBytes(cleaned, "$schema")
-					cleaned, _ = sjson.SetBytes(cleaned, "additionalProperties", false)
+					cleaned := cleanGeminiCodexToolParameters(prm)
 					tool, _ = sjson.SetRawBytes(tool, "parameters", cleaned)
 				}
 				tool, _ = sjson.SetBytes(tool, "strict", false)
@@ -342,7 +336,11 @@ func ConvertGeminiRequestToCodex(modelName string, inputRawJSON []byte, _ bool)
 		if typeValue.Type != gjson.String {
 			continue
 		}
-		out, _ = sjson.SetBytes(out, fullPath, strings.ToLower(typeValue.String()))
+		normalizedType := strings.ToLower(typeValue.String())
+		if normalizedType == typeValue.String() {
+			continue
+		}
+		out, _ = sjson.SetBytes(out, fullPath, normalizedType)
 	}
 
 	return out
@@ -357,7 +355,10 @@ func setCodexToolChoiceFromGeminiToolConfig(out []byte, functionCallingConfig gj
 	case "NONE":
 		out, _ = sjson.SetBytes(out, "tool_choice", "none")
 	case "AUTO":
-		out, _ = sjson.SetBytes(out, "tool_choice", "auto")
+		current := gjson.GetBytes(out, "tool_choice")
+		if current.Type != gjson.String || current.String() != "auto" {
+			out, _ = sjson.SetBytes(out, "tool_choice", "auto")
+		}
 	case "ANY":
 		allowedNames := functionCallingConfig.Get("allowedFunctionNames")
 		allowedNameItems := allowedNames.Array()
@@ -372,6 +373,17 @@ func setCodexToolChoiceFromGeminiToolConfig(out []byte, functionCallingConfig gj
 	return out
 }
 
+func cleanGeminiCodexToolParameters(parameters gjson.Result) []byte {
+	cleaned := []byte(parameters.Raw)
+	if parameters.Get("$schema").Exists() {
+		cleaned, _ = sjson.DeleteBytes(cleaned, "$schema")
+	}
+	if additionalProperties := parameters.Get("additionalProperties"); additionalProperties.Type != gjson.False {
+		cleaned, _ = sjson.SetBytes(cleaned, "additionalProperties", false)
+	}
+	return cleaned
+}
+
 func codexMessageWithPart(role string, part []byte) []byte {
 	msg := []byte(`{"type":"message","role":"","content":[]}`)
 	msg, _ = sjson.SetBytes(msg, "role", role)
diff --git a/internal/translator/codex/gemini/noop_optimization_test.go b/internal/translator/codex/gemini/noop_optimization_test.go
new file mode 100644
index 00000000..508382be
--- /dev/null
+++ b/internal/translator/codex/gemini/noop_optimization_test.go
@@ -0,0 +1,41 @@
+package gemini
+
+import (
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestCleanGeminiCodexToolParametersPreservesCanonicalSchema(t *testing.T) {
+	input := []byte(`{"type":"object","properties":{"value":{"type":"string"}},"additionalProperties":false}`)
+
+	output := cleanGeminiCodexToolParameters(gjson.ParseBytes(input))
+
+	if string(output) != string(input) {
+		t.Fatalf("canonical schema changed:\n got: %s\nwant: %s", output, input)
+	}
+}
+
+func TestSetCodexToolChoiceFromGeminiToolConfigReusesAutoChoice(t *testing.T) {
+	input := []byte(`{"tool_choice":"auto","input":[]}`)
+	config := gjson.Parse(`{"mode":"AUTO"}`)
+
+	output := setCodexToolChoiceFromGeminiToolConfig(input, config)
+
+	if &output[0] != &input[0] {
+		t.Fatal("AUTO tool choice caused a payload copy")
+	}
+}
+
+func TestCleanGeminiCodexToolParametersNormalizesSchema(t *testing.T) {
+	input := []byte(`{"type":"object","$schema":"draft","additionalProperties":true}`)
+
+	output := cleanGeminiCodexToolParameters(gjson.ParseBytes(input))
+
+	if gjson.GetBytes(output, "$schema").Exists() {
+		t.Fatal("$schema should be removed")
+	}
+	if additionalProperties := gjson.GetBytes(output, "additionalProperties"); additionalProperties.Type != gjson.False {
+		t.Fatalf("additionalProperties = %s, want false", additionalProperties.Raw)
+	}
+}
diff --git a/internal/translator/codex/interactions/interactions_codex_request.go b/internal/translator/codex/interactions/interactions_codex_request.go
index e37ad33f..89b083f2 100644
--- a/internal/translator/codex/interactions/interactions_codex_request.go
+++ b/internal/translator/codex/interactions/interactions_codex_request.go
@@ -348,19 +348,34 @@ func copyInteractionsToolsToCodex(out []byte, root gjson.Result) []byte {
 
 func copyInteractionsCodexTopLevel(out []byte, root gjson.Result) []byte {
 	if serviceTier := normalizeInteractionsCodexServiceTier(root.Get("service_tier")); serviceTier != "" {
-		out, _ = sjson.SetBytes(out, "service_tier", serviceTier)
+		current := gjson.GetBytes(out, "service_tier")
+		if current.Type != gjson.String || current.String() != serviceTier {
+			out, _ = sjson.SetBytes(out, "service_tier", serviceTier)
+		}
 	}
 	if toolChoice := root.Get("tool_choice"); toolChoice.Exists() {
-		out, _ = sjson.SetRawBytes(out, "tool_choice", []byte(toolChoice.Raw))
+		out = setInteractionsCodexRawIfDifferent(out, "tool_choice", toolChoice)
 	}
 	for _, path := range []string{"parallel_tool_calls", "store", "metadata", "include", "truncation"} {
 		if value := root.Get(path); value.Exists() {
-			out, _ = sjson.SetRawBytes(out, path, []byte(value.Raw))
+			out = setInteractionsCodexRawIfDifferent(out, path, value)
 		}
 	}
 	return out
 }
 
+func setInteractionsCodexRawIfDifferent(out []byte, path string, value gjson.Result) []byte {
+	current := gjson.GetBytes(out, path)
+	if current.Exists() && current.Raw == value.Raw {
+		return out
+	}
+	updated, errSet := sjson.SetRawBytes(out, path, []byte(value.Raw))
+	if errSet != nil {
+		return out
+	}
+	return updated
+}
+
 func appendInteractionsThoughtToCodex(items *[][]byte, step gjson.Result) {
 	text := interactionsCodexContentText(step.Get("content"))
 	if text == "" {
@@ -565,8 +580,12 @@ func codexToolFromDeclaration(declaration gjson.Result) map[string]any {
 
 func cleanedCodexToolParameters(params gjson.Result) json.RawMessage {
 	cleaned := []byte(params.Raw)
-	cleaned, _ = sjson.DeleteBytes(cleaned, "$schema")
-	cleaned, _ = sjson.SetBytes(cleaned, "additionalProperties", false)
+	if params.Get("$schema").Exists() {
+		cleaned, _ = sjson.DeleteBytes(cleaned, "$schema")
+	}
+	if params.Get("additionalProperties").Type != gjson.False {
+		cleaned, _ = sjson.SetBytes(cleaned, "additionalProperties", false)
+	}
 	return json.RawMessage(cleaned)
 }
 
diff --git a/internal/translator/codex/interactions/noop_optimization_test.go b/internal/translator/codex/interactions/noop_optimization_test.go
new file mode 100644
index 00000000..8b1da38f
--- /dev/null
+++ b/internal/translator/codex/interactions/noop_optimization_test.go
@@ -0,0 +1,28 @@
+package interactions
+
+import (
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestCleanedCodexToolParametersPreservesCanonicalSchema(t *testing.T) {
+	input := []byte(`{"type":"object","properties":{"value":{"type":"string"}},"additionalProperties":false}`)
+
+	output := []byte(cleanedCodexToolParameters(gjson.ParseBytes(input)))
+
+	if string(output) != string(input) {
+		t.Fatalf("canonical schema changed:\n got: %s\nwant: %s", output, input)
+	}
+}
+
+func TestSetInteractionsCodexRawIfDifferentReusesMatchingValue(t *testing.T) {
+	input := []byte(`{"tool_choice":"auto","input":[]}`)
+	value := gjson.Parse(`"auto"`)
+
+	output := setInteractionsCodexRawIfDifferent(input, "tool_choice", value)
+
+	if &output[0] != &input[0] {
+		t.Fatal("matching raw value caused a payload copy")
+	}
+}
diff --git a/internal/translator/codex/openai/chat-completions/codex_openai_response.go b/internal/translator/codex/openai/chat-completions/codex_openai_response.go
index 89bac12d..7feb9fdb 100644
--- a/internal/translator/codex/openai/chat-completions/codex_openai_response.go
+++ b/internal/translator/codex/openai/chat-completions/codex_openai_response.go
@@ -459,12 +459,10 @@ func ConvertCodexResponseToOpenAINonStream(_ context.Context, _ string, original
 		// Set content and reasoning content if found
 		if contentText != "" {
 			template, _ = sjson.SetBytes(template, "choices.0.message.content", contentText)
-			template, _ = sjson.SetBytes(template, "choices.0.message.role", "assistant")
 		}
 
 		if reasoningText != "" {
 			template, _ = sjson.SetBytes(template, "choices.0.message.reasoning_content", reasoningText)
-			template, _ = sjson.SetBytes(template, "choices.0.message.role", "assistant")
 		}
 
 		// Add tool calls if any
@@ -473,7 +471,6 @@ func ConvertCodexResponseToOpenAINonStream(_ context.Context, _ string, original
 			for _, toolCall := range toolCalls {
 				template, _ = sjson.SetRawBytes(template, "choices.0.message.tool_calls.-1", toolCall)
 			}
-			template, _ = sjson.SetBytes(template, "choices.0.message.role", "assistant")
 		}
 
 		// Add images if any
@@ -482,7 +479,6 @@ func ConvertCodexResponseToOpenAINonStream(_ context.Context, _ string, original
 			for _, image := range images {
 				template, _ = sjson.SetRawBytes(template, "choices.0.message.images.-1", image)
 			}
-			template, _ = sjson.SetBytes(template, "choices.0.message.role", "assistant")
 		}
 	}
 
diff --git a/internal/translator/codex/openai/chat-completions/noop_optimization_test.go b/internal/translator/codex/openai/chat-completions/noop_optimization_test.go
new file mode 100644
index 00000000..1f5f5db3
--- /dev/null
+++ b/internal/translator/codex/openai/chat-completions/noop_optimization_test.go
@@ -0,0 +1,18 @@
+package chat_completions
+
+import (
+	"context"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestConvertCodexResponseToOpenAINonStreamKeepsAssistantRole(t *testing.T) {
+	input := []byte(`{"type":"response.completed","response":{"status":"completed","output":[{"type":"message","content":[{"type":"output_text","text":"hello"}]}]}}`)
+
+	output := ConvertCodexResponseToOpenAINonStream(context.Background(), "", nil, nil, input, nil)
+
+	if role := gjson.GetBytes(output, "choices.0.message.role").String(); role != "assistant" {
+		t.Fatalf("role = %q, want assistant", role)
+	}
+}
diff --git a/internal/translator/gemini/claude/gemini_claude_request.go b/internal/translator/gemini/claude/gemini_claude_request.go
index f6641a5e..ac41628d 100644
--- a/internal/translator/gemini/claude/gemini_claude_request.go
+++ b/internal/translator/gemini/claude/gemini_claude_request.go
@@ -207,13 +207,17 @@ func ConvertClaudeRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 				if err != nil {
 					return true
 				}
-				tool, _ = sjson.DeleteBytes(tool, "strict")
-				tool, _ = sjson.DeleteBytes(tool, "input_examples")
-				tool, _ = sjson.DeleteBytes(tool, "type")
-				tool, _ = sjson.DeleteBytes(tool, "cache_control")
-				tool, _ = sjson.DeleteBytes(tool, "defer_loading")
-				tool, _ = sjson.DeleteBytes(tool, "eager_input_streaming")
-				tool, _ = sjson.SetBytes(tool, "name", util.SanitizeFunctionName(gjson.GetBytes(tool, "name").String()))
+				for _, path := range []string{"strict", "input_examples", "type", "cache_control", "defer_loading", "eager_input_streaming"} {
+					if toolResult.Get(path).Exists() {
+						tool, _ = sjson.DeleteBytes(tool, path)
+					}
+				}
+				nameResult := toolResult.Get("name")
+				originalName := nameResult.String()
+				sanitizedName := util.SanitizeFunctionName(originalName)
+				if nameResult.Type != gjson.String || sanitizedName != originalName {
+					tool, _ = sjson.SetBytes(tool, "name", sanitizedName)
+				}
 				if gjson.ValidBytes(tool) && gjson.ParseBytes(tool).IsObject() {
 					toolItems = append(toolItems, tool)
 				}
@@ -224,8 +228,6 @@ func ConvertClaudeRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 			tools := []byte(`[{"functionDeclarations":[]}]`)
 			tools, _ = sjson.SetRawBytes(tools, "0.functionDeclarations", translatorcommon.JoinRawArray(toolItems))
 			out, _ = sjson.SetRawBytes(out, "tools", tools)
-		} else {
-			out, _ = sjson.DeleteBytes(out, "tools")
 		}
 	}
 
diff --git a/internal/translator/gemini/openai/chat-completions/gemini_openai_request.go b/internal/translator/gemini/openai/chat-completions/gemini_openai_request.go
index abbb2dd0..c6a2dd80 100644
--- a/internal/translator/gemini/openai/chat-completions/gemini_openai_request.go
+++ b/internal/translator/gemini/openai/chat-completions/gemini_openai_request.go
@@ -350,13 +350,22 @@ func ConvertOpenAIRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 						fnRaw = string(fnRawBytes)
 					}
 					fnRawBytes := []byte(fnRaw)
-					fnRawBytes, _ = sjson.SetBytes(fnRawBytes, "name", util.SanitizeFunctionName(fn.Get("name").String()))
-					fnRaw = string(fnRawBytes)
-					if parameters := gjson.Get(fnRaw, "parametersJsonSchema"); parameters.Exists() {
-						fnRaw, _ = sjson.SetRaw(fnRaw, "parametersJsonSchema", util.CleanJSONSchemaForGemini(parameters.Raw))
+					nameResult := fn.Get("name")
+					originalName := nameResult.String()
+					sanitizedName := util.SanitizeFunctionName(originalName)
+					if nameResult.Type != gjson.String || sanitizedName != originalName {
+						fnRawBytes, _ = sjson.SetBytes(fnRawBytes, "name", sanitizedName)
 					}
-					fnRaw, _ = sjson.Delete(fnRaw, "strict")
-					functionDeclarations = append(functionDeclarations, []byte(fnRaw))
+					if parameters := gjson.GetBytes(fnRawBytes, "parametersJsonSchema"); parameters.Exists() {
+						cleanedParameters := util.CleanJSONSchemaForGemini(parameters.Raw)
+						if cleanedParameters != parameters.Raw {
+							fnRawBytes, _ = sjson.SetRawBytes(fnRawBytes, "parametersJsonSchema", []byte(cleanedParameters))
+						}
+					}
+					if gjson.GetBytes(fnRawBytes, "strict").Exists() {
+						fnRawBytes, _ = sjson.DeleteBytes(fnRawBytes, "strict")
+					}
+					functionDeclarations = append(functionDeclarations, fnRawBytes)
 				}
 			}
 			if gs := t.Get("google_search"); gs.Exists() {
diff --git a/internal/translator/gemini/openai/chat-completions/gemini_openai_response.go b/internal/translator/gemini/openai/chat-completions/gemini_openai_response.go
index 155a8c5f..cb44c258 100644
--- a/internal/translator/gemini/openai/chat-completions/gemini_openai_response.go
+++ b/internal/translator/gemini/openai/chat-completions/gemini_openai_response.go
@@ -150,6 +150,14 @@ func ConvertGeminiResponseToOpenAI(_ context.Context, _ string, originalRequestR
 			}
 
 			partsResult := candidate.Get("content.parts")
+			assistantRoleSet := false
+			setAssistantRole := func() {
+				if assistantRoleSet {
+					return
+				}
+				template, _ = sjson.SetBytes(template, "choices.0.delta.role", "assistant")
+				assistantRoleSet = true
+			}
 
 			if partsResult.IsArray() {
 				partResults := partsResult.Array()
@@ -176,13 +184,13 @@ func ConvertGeminiResponseToOpenAI(_ context.Context, _ string, originalRequestR
 
 					if partTextResult.Exists() {
 						text := partTextResult.String()
+						setAssistantRole()
 						// Handle text content, distinguishing between regular content and reasoning/thoughts.
 						if partResult.Get("thought").Bool() {
 							template, _ = sjson.SetBytes(template, "choices.0.delta.reasoning_content", text)
 						} else {
 							template, _ = sjson.SetBytes(template, "choices.0.delta.content", text)
 						}
-						template, _ = sjson.SetBytes(template, "choices.0.delta.role", "assistant")
 					} else if functionCallResult.Exists() {
 						// Handle function call content.
 						p.SawToolCall[candidateIndex] = true
@@ -206,7 +214,7 @@ func ConvertGeminiResponseToOpenAI(_ context.Context, _ string, originalRequestR
 						if fcArgsResult := functionCallResult.Get("args"); fcArgsResult.Exists() {
 							functionCallTemplate, _ = sjson.SetBytes(functionCallTemplate, "function.arguments", fcArgsResult.Raw)
 						}
-						template, _ = sjson.SetBytes(template, "choices.0.delta.role", "assistant")
+						setAssistantRole()
 						template, _ = sjson.SetRawBytes(template, "choices.0.delta.tool_calls.-1", functionCallTemplate)
 					} else if inlineDataResult.Exists() {
 						data := inlineDataResult.Get("data").String()
@@ -229,7 +237,7 @@ func ConvertGeminiResponseToOpenAI(_ context.Context, _ string, originalRequestR
 						imagePayload := []byte(`{"type":"image_url","image_url":{"url":""}}`)
 						imagePayload, _ = sjson.SetBytes(imagePayload, "index", imageIndex)
 						imagePayload, _ = sjson.SetBytes(imagePayload, "image_url.url", imageURL)
-						template, _ = sjson.SetBytes(template, "choices.0.delta.role", "assistant")
+						setAssistantRole()
 						template, _ = sjson.SetRawBytes(template, "choices.0.delta.images.-1", imagePayload)
 					}
 				}
@@ -365,7 +373,6 @@ func ConvertGeminiResponseToOpenAINonStream(_ context.Context, _ string, origina
 							oldVal := gjson.GetBytes(choiceTemplate, "message.content").String()
 							choiceTemplate, _ = sjson.SetBytes(choiceTemplate, "message.content", oldVal+partTextResult.String())
 						}
-						choiceTemplate, _ = sjson.SetBytes(choiceTemplate, "message.role", "assistant")
 					} else if functionCallResult.Exists() {
 						// Append function call content to the tool_calls array.
 						hasFunctionCall = true
@@ -380,7 +387,6 @@ func ConvertGeminiResponseToOpenAINonStream(_ context.Context, _ string, origina
 						if fcArgsResult := functionCallResult.Get("args"); fcArgsResult.Exists() {
 							functionCallItemTemplate, _ = sjson.SetBytes(functionCallItemTemplate, "function.arguments", fcArgsResult.Raw)
 						}
-						choiceTemplate, _ = sjson.SetBytes(choiceTemplate, "message.role", "assistant")
 						choiceTemplate, _ = sjson.SetRawBytes(choiceTemplate, "message.tool_calls.-1", functionCallItemTemplate)
 					} else if inlineDataResult.Exists() {
 						data := inlineDataResult.Get("data").String()
@@ -401,7 +407,6 @@ func ConvertGeminiResponseToOpenAINonStream(_ context.Context, _ string, origina
 							imagePayload := []byte(`{"type":"image_url","image_url":{"url":""}}`)
 							imagePayload, _ = sjson.SetBytes(imagePayload, "index", imageIndex)
 							imagePayload, _ = sjson.SetBytes(imagePayload, "image_url.url", imageURL)
-							choiceTemplate, _ = sjson.SetBytes(choiceTemplate, "message.role", "assistant")
 							choiceTemplate, _ = sjson.SetRawBytes(choiceTemplate, "message.images.-1", imagePayload)
 						}
 					}
diff --git a/internal/translator/gemini/openai/chat-completions/noop_optimization_test.go b/internal/translator/gemini/openai/chat-completions/noop_optimization_test.go
new file mode 100644
index 00000000..b69d0f3d
--- /dev/null
+++ b/internal/translator/gemini/openai/chat-completions/noop_optimization_test.go
@@ -0,0 +1,55 @@
+package chat_completions
+
+import (
+	"context"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestConvertOpenAIRequestToGeminiNormalizesToolNameAndStrict(t *testing.T) {
+	input := []byte(`{"messages":[],"tools":[{"type":"function","function":{"name":true,"strict":true,"parameters":{"type":"object"}}}]}`)
+
+	output := ConvertOpenAIRequestToGemini("gemini-test", input, false)
+
+	name := gjson.GetBytes(output, "tools.0.functionDeclarations.0.name")
+	if name.Type != gjson.String || name.String() != "true" {
+		t.Fatalf("tool name = %s, want string true", name.Raw)
+	}
+	if gjson.GetBytes(output, "tools.0.functionDeclarations.0.strict").Exists() {
+		t.Fatal("strict should be removed")
+	}
+}
+
+func TestConvertGeminiResponseToOpenAINonStreamKeepsAssistantRole(t *testing.T) {
+	input := []byte(`{"candidates":[{"index":0,"content":{"parts":[{"text":"hello"}]},"finishReason":"STOP"}]}`)
+
+	output := ConvertGeminiResponseToOpenAINonStream(context.Background(), "", nil, nil, input, nil)
+
+	if role := gjson.GetBytes(output, "choices.0.message.role").String(); role != "assistant" {
+		t.Fatalf("role = %q, want assistant", role)
+	}
+}
+
+func TestConvertGeminiResponseToOpenAIStreamingSetsAssistantRoleOnce(t *testing.T) {
+	input := []byte(`{"candidates":[{"index":0,"content":{"parts":[{"text":"hello"},{"functionCall":{"name":"lookup","args":{}}},{"inlineData":{"mimeType":"image/png","data":"aGVsbG8="}}]}}]}`)
+	var param any
+
+	outputs := ConvertGeminiResponseToOpenAI(context.Background(), "", nil, nil, input, &param)
+
+	if len(outputs) != 1 {
+		t.Fatalf("output count = %d, want 1", len(outputs))
+	}
+	if role := gjson.GetBytes(outputs[0], "choices.0.delta.role").String(); role != "assistant" {
+		t.Fatalf("role = %q, want assistant", role)
+	}
+	if got := gjson.GetBytes(outputs[0], "choices.0.delta.content").String(); got != "hello" {
+		t.Fatalf("content = %q, want hello", got)
+	}
+	if !gjson.GetBytes(outputs[0], "choices.0.delta.tool_calls.0").Exists() {
+		t.Fatal("tool call should be present")
+	}
+	if !gjson.GetBytes(outputs[0], "choices.0.delta.images.0").Exists() {
+		t.Fatal("image should be present")
+	}
+}
diff --git a/internal/translator/gemini/openai/responses/gemini_openai-responses_request.go b/internal/translator/gemini/openai/responses/gemini_openai-responses_request.go
index 21e2d2e6..81621a3f 100644
--- a/internal/translator/gemini/openai/responses/gemini_openai-responses_request.go
+++ b/internal/translator/gemini/openai/responses/gemini_openai-responses_request.go
@@ -32,7 +32,6 @@ func ConvertOpenAIResponsesRequestToGemini(modelName string, inputRawJSON []byte
 		part := []byte(`{"text":""}`)
 		part, _ = sjson.SetBytes(part, "text", instructions.String())
 		systemParts = append(systemParts, part)
-		out, _ = sjson.SetRawBytes(out, "systemInstruction", geminiSystemInstruction(systemParts))
 	}
 
 	// Convert input messages to Gemini contents format
@@ -409,25 +408,16 @@ func ConvertOpenAIResponsesRequestToGemini(modelName string, inputRawJSON []byte
 
 	// Handle temperature if present
 	if temperature := root.Get("temperature"); temperature.Exists() {
-		if !gjson.GetBytes(out, "generationConfig").Exists() {
-			out, _ = sjson.SetRawBytes(out, "generationConfig", []byte(`{}`))
-		}
 		out, _ = sjson.SetBytes(out, "generationConfig.temperature", temperature.Float())
 	}
 
 	// Handle top_p if present
 	if topP := root.Get("top_p"); topP.Exists() {
-		if !gjson.GetBytes(out, "generationConfig").Exists() {
-			out, _ = sjson.SetRawBytes(out, "generationConfig", []byte(`{}`))
-		}
 		out, _ = sjson.SetBytes(out, "generationConfig.topP", topP.Float())
 	}
 
 	// Handle stop sequences
 	if stopSequences := root.Get("stop_sequences"); stopSequences.Exists() && stopSequences.IsArray() {
-		if !gjson.GetBytes(out, "generationConfig").Exists() {
-			out, _ = sjson.SetRawBytes(out, "generationConfig", []byte(`{}`))
-		}
 		var sequences []string
 		stopSequences.ForEach(func(_, seq gjson.Result) bool {
 			sequences = append(sequences, seq.String())
@@ -594,12 +584,9 @@ func applyOpenAIResponsesTextFormatToGemini(out []byte, root gjson.Result) []byt
 	formatType := strings.ToLower(strings.TrimSpace(textFormat.Get("type").String()))
 	switch formatType {
 	case "json_object":
-		out = ensureGeminiGenerationConfig(out)
 		out, _ = sjson.SetBytes(out, "generationConfig.responseMimeType", "application/json")
 	case "json_schema":
-		out = ensureGeminiGenerationConfig(out)
 		out, _ = sjson.SetBytes(out, "generationConfig.responseMimeType", "application/json")
-		out, _ = sjson.DeleteBytes(out, "generationConfig.responseSchema")
 
 		schema := textFormat.Get("schema")
 		if !schema.Exists() {
@@ -612,10 +599,3 @@ func applyOpenAIResponsesTextFormatToGemini(out []byte, root gjson.Result) []byt
 
 	return out
 }
-
-func ensureGeminiGenerationConfig(out []byte) []byte {
-	if !gjson.GetBytes(out, "generationConfig").Exists() {
-		out, _ = sjson.SetRawBytes(out, "generationConfig", []byte(`{}`))
-	}
-	return out
-}
diff --git a/internal/translator/gemini/openai/responses/noop_optimization_test.go b/internal/translator/gemini/openai/responses/noop_optimization_test.go
new file mode 100644
index 00000000..255ab295
--- /dev/null
+++ b/internal/translator/gemini/openai/responses/noop_optimization_test.go
@@ -0,0 +1,32 @@
+package responses
+
+import (
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestConvertOpenAIResponsesRequestToGeminiBuildsGenerationConfigWithoutIntermediateObject(t *testing.T) {
+	input := []byte(`{"input":"hello","temperature":0.5,"top_p":0.9,"stop_sequences":["done"],"text":{"format":{"type":"json_schema","schema":{"type":"object"}}}}`)
+
+	output := ConvertOpenAIResponsesRequestToGemini("gemini-test", input, false)
+
+	if got := gjson.GetBytes(output, "generationConfig.temperature").Float(); got != 0.5 {
+		t.Fatalf("temperature = %v, want 0.5", got)
+	}
+	if got := gjson.GetBytes(output, "generationConfig.topP").Float(); got != 0.9 {
+		t.Fatalf("topP = %v, want 0.9", got)
+	}
+	if got := gjson.GetBytes(output, "generationConfig.stopSequences.0").String(); got != "done" {
+		t.Fatalf("stop sequence = %q, want done", got)
+	}
+	if got := gjson.GetBytes(output, "generationConfig.responseMimeType").String(); got != "application/json" {
+		t.Fatalf("responseMimeType = %q, want application/json", got)
+	}
+	if !gjson.GetBytes(output, "generationConfig.responseJsonSchema").Exists() {
+		t.Fatal("responseJsonSchema should be present")
+	}
+	if gjson.GetBytes(output, "generationConfig.responseSchema").Exists() {
+		t.Fatal("responseSchema should not be present")
+	}
+}
diff --git a/internal/translator/openai/openai/chat-completions/openai_openai_request.go b/internal/translator/openai/openai/chat-completions/openai_openai_request.go
index f2e6fadc..dd3ee5ab 100644
--- a/internal/translator/openai/openai/chat-completions/openai_openai_request.go
+++ b/internal/translator/openai/openai/chat-completions/openai_openai_request.go
@@ -3,6 +3,7 @@
 package chat_completions
 
 import (
+	"github.com/tidwall/gjson"
 	"github.com/tidwall/sjson"
 )
 
@@ -17,6 +18,11 @@ import (
 // Returns:
 //   - []byte: The transformed request data in OpenAI API format
 func ConvertOpenAIRequestToOpenAI(modelName string, inputRawJSON []byte, _ bool) []byte {
+	currentModel := gjson.GetBytes(inputRawJSON, "model")
+	if currentModel.Type == gjson.String && currentModel.String() == modelName {
+		return inputRawJSON
+	}
+
 	// Update the "model" field in the JSON payload with the provided modelName
 	// The sjson.SetBytes function returns a new byte slice with the updated JSON.
 	updatedJSON, err := sjson.SetBytes(inputRawJSON, "model", modelName)
diff --git a/internal/translator/openai/openai/chat-completions/openai_openai_request_test.go b/internal/translator/openai/openai/chat-completions/openai_openai_request_test.go
new file mode 100644
index 00000000..80a71a28
--- /dev/null
+++ b/internal/translator/openai/openai/chat-completions/openai_openai_request_test.go
@@ -0,0 +1,27 @@
+package chat_completions
+
+import (
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestConvertOpenAIRequestToOpenAIReusesMatchingModelPayload(t *testing.T) {
+	input := []byte(`{"model":"gpt-test","messages":[{"role":"user","content":"hello"}]}`)
+
+	output := ConvertOpenAIRequestToOpenAI("gpt-test", input, false)
+
+	if &output[0] != &input[0] {
+		t.Fatal("matching model caused a payload copy")
+	}
+}
+
+func TestConvertOpenAIRequestToOpenAIUpdatesDifferentModel(t *testing.T) {
+	input := []byte(`{"model":"old-model","messages":[]}`)
+
+	output := ConvertOpenAIRequestToOpenAI("new-model", input, false)
+
+	if model := gjson.GetBytes(output, "model").String(); model != "new-model" {
+		t.Fatalf("model = %q, want new-model", model)
+	}
+}
diff --git a/internal/translator/request_benchmark_test.go b/internal/translator/request_benchmark_test.go
index 333a4a01..3e7c0f01 100644
--- a/internal/translator/request_benchmark_test.go
+++ b/internal/translator/request_benchmark_test.go
@@ -1,6 +1,7 @@
 package translator
 
 import (
+	"bytes"
 	"encoding/json"
 	"fmt"
 	"strings"
@@ -10,6 +11,10 @@ import (
 	"github.com/tidwall/gjson"
 )
 
+const benchmarkHistorySentinel = "benchmark-final-history-turn"
+
+var benchmarkRequestTranslationOutput []byte
+
 func BenchmarkRequestTranslationLargeHistory(b *testing.B) {
 	benchmarkRequestTranslation(b, 64)
 }
@@ -36,7 +41,7 @@ func benchmarkRequestTranslation(b *testing.B, turns int) {
 	}{
 		{source: "claude", targets: []string{"openai", "gemini", "codex", "interactions", "antigravity"}},
 		{source: "gemini", targets: []string{"openai", "claude", "codex", "interactions", "antigravity", "gemini"}},
-		{source: "openai", targets: []string{"claude", "gemini", "codex", "interactions", "antigravity"}},
+		{source: "openai", targets: []string{"claude", "gemini", "codex", "interactions", "antigravity", "openai"}},
 		{source: "openai-response", targets: []string{"claude", "gemini", "codex", "interactions", "openai"}},
 		{source: "interactions", targets: []string{"claude", "gemini", "codex", "openai", "openai-response", "antigravity"}},
 	}
@@ -45,14 +50,18 @@ func benchmarkRequestTranslation(b *testing.B, turns int) {
 		request := requests[route.source]
 		for _, target := range route.targets {
 			b.Run(route.source+"_to_"+target, func(b *testing.B) {
-				if output := translatorapi.Request(route.source, target, "gemini-2.5-pro", request, true); !gjson.ValidBytes(output) {
+				output := translatorapi.Request(route.source, target, "gemini-2.5-pro", request, true)
+				if !gjson.ValidBytes(output) {
 					b.Fatalf("translator generated invalid JSON: %s", output)
 				}
+				if turns > 0 && !bytes.Contains(output, []byte(benchmarkHistorySentinel)) {
+					b.Fatal("translator dropped the final benchmark history turn")
+				}
 				b.ReportAllocs()
 				b.SetBytes(int64(len(request)))
 				b.ResetTimer()
-				for i := 0; i < b.N; i++ {
-					translatorapi.Request(route.source, target, "gemini-2.5-pro", request, true)
+				for b.Loop() {
+					benchmarkRequestTranslationOutput = translatorapi.Request(route.source, target, "gemini-2.5-pro", request, true)
 				}
 			})
 		}
@@ -74,6 +83,9 @@ func benchmarkClaudeRequest(turns int) []byte {
 			}},
 		)
 	}
+	if turns > 0 {
+		messages = append(messages, map[string]any{"role": "user", "content": benchmarkHistorySentinel})
+	}
 	return benchmarkJSON(map[string]any{
 		"system":   []any{map[string]any{"type": "text", "text": payload}},
 		"messages": messages,
@@ -96,6 +108,9 @@ func benchmarkGeminiRequest(turns int) []byte {
 			}},
 		)
 	}
+	if turns > 0 {
+		contents = append(contents, map[string]any{"role": "user", "parts": []any{map[string]any{"text": benchmarkHistorySentinel}}})
+	}
 	return benchmarkJSON(map[string]any{
 		"system_instruction": map[string]any{"parts": []any{map[string]any{"text": payload}}},
 		"contents":           contents,
@@ -118,7 +133,11 @@ func benchmarkOpenAIRequest(turns int) []byte {
 			map[string]any{"role": "tool", "tool_call_id": callID, "content": payload},
 		)
 	}
+	if turns > 0 {
+		messages = append(messages, map[string]any{"role": "user", "content": benchmarkHistorySentinel})
+	}
 	return benchmarkJSON(map[string]any{
+		"model":    "gemini-2.5-pro",
 		"messages": messages,
 		"tools": []any{map[string]any{"type": "function", "function": map[string]any{
 			"name": "lookup", "description": payload, "parameters": benchmarkSchema(),
@@ -137,6 +156,9 @@ func benchmarkOpenAIResponsesRequest(turns int) []byte {
 			map[string]any{"type": "function_call_output", "call_id": callID, "output": payload},
 		)
 	}
+	if turns > 0 {
+		input = append(input, map[string]any{"type": "message", "role": "user", "content": []any{map[string]any{"type": "input_text", "text": benchmarkHistorySentinel}}})
+	}
 	return benchmarkJSON(map[string]any{
 		"instructions": payload,
 		"input":        input,
@@ -157,6 +179,9 @@ func benchmarkInteractionsRequest(turns int) []byte {
 			map[string]any{"type": "function_result", "call_id": callID, "name": "lookup", "result": payload},
 		)
 	}
+	if turns > 0 {
+		input = append(input, map[string]any{"type": "user_input", "content": []any{map[string]any{"type": "text", "text": benchmarkHistorySentinel}}})
+	}
 	return benchmarkJSON(map[string]any{
 		"system_instruction": payload,
 		"input":              input,
diff --git a/internal/translator/response_benchmark_test.go b/internal/translator/response_benchmark_test.go
new file mode 100644
index 00000000..32c0eec5
--- /dev/null
+++ b/internal/translator/response_benchmark_test.go
@@ -0,0 +1,74 @@
+package translator
+
+import (
+	"bytes"
+	"context"
+	"strings"
+	"testing"
+
+	translatorapi "github.com/router-for-me/CLIProxyAPI/v7/internal/translator/translator"
+	"github.com/tidwall/gjson"
+)
+
+var benchmarkResponseTranslationOutput []byte
+
+func BenchmarkResponseTranslationLargePayload(b *testing.B) {
+	payload := strings.Repeat("x", 8<<20)
+	cases := []struct {
+		name    string
+		from    string
+		to      string
+		rawJSON []byte
+	}{
+		{
+			name:    "gemini_to_openai",
+			from:    "gemini",
+			to:      "openai",
+			rawJSON: []byte(`{"modelVersion":"gemini-test","candidates":[{"index":0,"content":{"parts":[{"text":"` + payload + `"}]},"finishReason":"STOP"}]}`),
+		},
+		{
+			name:    "codex_to_openai",
+			from:    "codex",
+			to:      "openai",
+			rawJSON: []byte(`{"type":"response.completed","response":{"id":"resp_1","created_at":1700000000,"model":"gpt-test","status":"completed","output":[{"type":"message","content":[{"type":"output_text","text":"` + payload + `"}]}]}}`),
+		},
+		{
+			name:    "claude_to_openai",
+			from:    "claude",
+			to:      "openai",
+			rawJSON: claudeLargeTextResponse(payload),
+		},
+		{
+			name:    "claude_to_openai-response",
+			from:    "claude",
+			to:      "openai-response",
+			rawJSON: claudeLargeTextResponse(payload),
+		},
+	}
+
+	for _, testCase := range cases {
+		b.Run(testCase.name, func(b *testing.B) {
+			output := translatorapi.ResponseNonStream(testCase.from, testCase.to, context.Background(), "benchmark-model", nil, nil, testCase.rawJSON, nil)
+			if !gjson.ValidBytes(output) {
+				b.Fatalf("translator generated invalid JSON: %s", output)
+			}
+			if !bytes.Contains(output, []byte(payload)) {
+				b.Fatal("translator dropped the benchmark payload")
+			}
+			b.ReportAllocs()
+			b.SetBytes(int64(len(testCase.rawJSON)))
+			b.ResetTimer()
+
+			for b.Loop() {
+				benchmarkResponseTranslationOutput = translatorapi.ResponseNonStream(testCase.from, testCase.to, context.Background(), "benchmark-model", nil, nil, testCase.rawJSON, nil)
+			}
+		})
+	}
+}
+
+func claudeLargeTextResponse(payload string) []byte {
+	return []byte("data: {\"type\":\"message_start\",\"message\":{\"id\":\"msg_1\",\"model\":\"claude-test\"}}\n" +
+		"data: {\"type\":\"content_block_start\",\"index\":0,\"content_block\":{\"type\":\"text\"}}\n" +
+		"data: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"text_delta\",\"text\":\"" + payload + "\"}}\n" +
+		"data: {\"type\":\"message_delta\",\"delta\":{\"stop_reason\":\"end_turn\"}}\n")
+}