diff --git a/internal/translator/antigravity/gemini/antigravity_gemini_request.go b/internal/translator/antigravity/gemini/antigravity_gemini_request.go
index b33b9c40e..f00821755 100644
--- a/internal/translator/antigravity/gemini/antigravity_gemini_request.go
+++ b/internal/translator/antigravity/gemini/antigravity_gemini_request.go
@@ -99,35 +99,19 @@ func ConvertGeminiRequestToAntigravity(modelName string, inputRawJSON []byte, _
 	}
 
 	// Gemini-specific handling for non-Claude models:
-	// - Add skip_thought_signature_validator to functionCall parts so upstream can bypass signature validation.
-	// - Also mark thinking parts with the same sentinel when present (we keep the parts; we only annotate them).
-	if !strings.Contains(modelName, "claude") {
+	// - Replace client-provided thoughtSignature values with the skip sentinel.
+	// - Add the same sentinel to functionCall and thinking parts so upstream can bypass signature validation.
+	if !strings.Contains(strings.ToLower(modelName), "claude") {
 		const skipSentinel = "skip_thought_signature_validator"
 
 		gjson.GetBytes(rawJSON, "request.contents").ForEach(func(contentIdx, content gjson.Result) bool {
 			if content.Get("role").String() == "model" {
-				// First pass: collect indices of thinking parts to mark with skip sentinel
-				var thinkingIndicesToSkipSignature []int64
 				content.Get("parts").ForEach(func(partIdx, part gjson.Result) bool {
-					// Collect indices of thinking blocks to mark with skip sentinel
-					if part.Get("thought").Bool() {
-						thinkingIndicesToSkipSignature = append(thinkingIndicesToSkipSignature, partIdx.Int())
-					}
-					// Add skip sentinel to functionCall parts
-					if part.Get("functionCall").Exists() {
-						existingSig := part.Get("thoughtSignature").String()
-						if existingSig == "" || len(existingSig) < 50 {
-							rawJSON, _ = sjson.SetBytes(rawJSON, fmt.Sprintf("request.contents.%d.parts.%d.thoughtSignature", contentIdx.Int(), partIdx.Int()), skipSentinel)
-						}
+					if part.Get("functionCall").Exists() || part.Get("thought").Exists() || part.Get("thoughtSignature").Exists() {
+						rawJSON, _ = sjson.SetBytes(rawJSON, fmt.Sprintf("request.contents.%d.parts.%d.thoughtSignature", contentIdx.Int(), partIdx.Int()), skipSentinel)
 					}
 					return true
 				})
-
-				// Add skip_thought_signature_validator sentinel to thinking blocks in reverse order to preserve indices
-				for i := len(thinkingIndicesToSkipSignature) - 1; i >= 0; i-- {
-					idx := thinkingIndicesToSkipSignature[i]
-					rawJSON, _ = sjson.SetBytes(rawJSON, fmt.Sprintf("request.contents.%d.parts.%d.thoughtSignature", contentIdx.Int(), idx), skipSentinel)
-				}
 			}
 			return true
 		})
diff --git a/internal/translator/antigravity/gemini/antigravity_gemini_request_test.go b/internal/translator/antigravity/gemini/antigravity_gemini_request_test.go
index 7e9e3bba8..3ee381d89 100644
--- a/internal/translator/antigravity/gemini/antigravity_gemini_request_test.go
+++ b/internal/translator/antigravity/gemini/antigravity_gemini_request_test.go
@@ -7,8 +7,8 @@ import (
 	"github.com/tidwall/gjson"
 )
 
-func TestConvertGeminiRequestToAntigravity_PreserveValidSignature(t *testing.T) {
-	// Valid signature on functionCall should be preserved
+func TestConvertGeminiRequestToAntigravity_ReplacesClientSignatureOnFunctionCall(t *testing.T) {
+	// Client signatures on Gemini function calls are not portable to Antigravity.
 	validSignature := "abc123validSignature1234567890123456789012345678901234567890"
 	inputJSON := []byte(fmt.Sprintf(`{
 		"model": "gemini-3-pro-preview",
@@ -25,15 +25,83 @@ func TestConvertGeminiRequestToAntigravity_PreserveValidSignature(t *testing.T)
 	output := ConvertGeminiRequestToAntigravity("gemini-3-pro-preview", inputJSON, false)
 	outputStr := string(output)
 
-	// Check that valid thoughtSignature is preserved
 	parts := gjson.Get(outputStr, "request.contents.0.parts").Array()
 	if len(parts) != 1 {
 		t.Fatalf("Expected 1 part, got %d", len(parts))
 	}
 
 	sig := parts[0].Get("thoughtSignature").String()
-	if sig != validSignature {
-		t.Errorf("Expected thoughtSignature '%s', got '%s'", validSignature, sig)
+	expectedSig := "skip_thought_signature_validator"
+	if sig != expectedSig {
+		t.Errorf("Expected thoughtSignature '%s', got '%s'", expectedSig, sig)
+	}
+}
+
+func TestConvertGeminiRequestToAntigravity_ReplacesClientSignatureOnTextPart(t *testing.T) {
+	validSignature := "abc123validSignature1234567890123456789012345678901234567890"
+	inputJSON := []byte(fmt.Sprintf(`{
+		"model": "gemini-3-pro-preview",
+		"contents": [
+			{
+				"role": "model",
+				"parts": [
+					{"text": "previous answer", "thoughtSignature": "%s"}
+				]
+			}
+		]
+	}`, validSignature))
+
+	output := ConvertGeminiRequestToAntigravity("gemini-3-pro-preview", inputJSON, false)
+	outputStr := string(output)
+
+	sig := gjson.Get(outputStr, "request.contents.0.parts.0.thoughtSignature").String()
+	expectedSig := "skip_thought_signature_validator"
+	if sig != expectedSig {
+		t.Errorf("Expected thoughtSignature '%s', got '%s'", expectedSig, sig)
+	}
+}
+
+func TestConvertGeminiRequestToAntigravity_AddsSkipSentinelToStringThoughtPart(t *testing.T) {
+	inputJSON := []byte(`{
+		"model": "gemini-3-pro-preview",
+		"contents": [
+			{
+				"role": "model",
+				"parts": [
+					{"thought": "internal reasoning"}
+				]
+			}
+		]
+	}`)
+
+	output := ConvertGeminiRequestToAntigravity("gemini-3-pro-preview", inputJSON, false)
+	outputStr := string(output)
+
+	sig := gjson.Get(outputStr, "request.contents.0.parts.0.thoughtSignature").String()
+	expectedSig := "skip_thought_signature_validator"
+	if sig != expectedSig {
+		t.Errorf("Expected thoughtSignature '%s', got '%s'", expectedSig, sig)
+	}
+}
+
+func TestConvertGeminiRequestToAntigravity_SkipsUppercaseClaudeModel(t *testing.T) {
+	inputJSON := []byte(`{
+		"model": "Claude-Test",
+		"contents": [
+			{
+				"role": "model",
+				"parts": [
+					{"functionCall": {"name": "test_tool", "args": {}}}
+				]
+			}
+		]
+	}`)
+
+	output := ConvertGeminiRequestToAntigravity("Claude-Test", inputJSON, false)
+	outputStr := string(output)
+
+	if sig := gjson.Get(outputStr, "request.contents.0.parts.0.thoughtSignature"); sig.Exists() {
+		t.Fatalf("Expected no thoughtSignature for Claude model, got %s", sig.Raw)
 	}
 }