diff --git a/internal/registry/model_registry.go b/internal/registry/model_registry.go
index 40221631..252aaffd 100644
--- a/internal/registry/model_registry.go
+++ b/internal/registry/model_registry.go
@@ -1161,7 +1161,7 @@ func (r *ModelRegistry) convertModelToMap(model *ModelInfo, handlerType string)
 			"owned_by": model.OwnedBy,
 		}
 		if model.Created > 0 {
-			result["created_at"] = model.Created
+			result["created_at"] = time.Unix(model.Created, 0).UTC().Format(time.RFC3339)
 		}
 		if model.Type != "" {
 			result["type"] = "model"
diff --git a/internal/registry/model_registry_cache_test.go b/internal/registry/model_registry_cache_test.go
index fc08c3d7..1951b433 100644
--- a/internal/registry/model_registry_cache_test.go
+++ b/internal/registry/model_registry_cache_test.go
@@ -25,7 +25,7 @@ func TestGetAvailableModelsReturnsClonedSnapshots(t *testing.T) {
 func TestGetAvailableModelsClaudeIncludesTokenLimits(t *testing.T) {
 	r := newTestModelRegistry()
 	r.RegisterClient("client-1", "Claude", []*ModelInfo{
-		{ID: "claude-sonnet-4-6", OwnedBy: "anthropic", Type: "claude", ContextLength: 200000, MaxCompletionTokens: 64000},
+		{ID: "claude-sonnet-4-6", OwnedBy: "anthropic", Type: "claude", Created: 1771372800, ContextLength: 200000, MaxCompletionTokens: 64000},
 		{ID: "claude-no-limits", OwnedBy: "anthropic", Type: "claude"},
 	})
 
@@ -46,6 +46,9 @@ func TestGetAvailableModelsClaudeIncludesTokenLimits(t *testing.T) {
 	if got := withLimits["max_tokens"]; got != 64000 {
 		t.Fatalf("expected max_tokens 64000, got %v", got)
 	}
+	if got := withLimits["created_at"]; got != "2026-02-18T00:00:00Z" {
+		t.Fatalf("expected created_at as RFC 3339 string, got %v", got)
+	}
 
 	withDefaults, ok := byID["claude-no-limits"]
 	if !ok {