diff --git a/internal/translator/gemini/claude/gemini_claude_response.go b/internal/translator/gemini/claude/gemini_claude_response.go
index ddded1fd8..d024d6f9a 100644
--- a/internal/translator/gemini/claude/gemini_claude_response.go
+++ b/internal/translator/gemini/claude/gemini_claude_response.go
@@ -304,6 +304,7 @@ func ConvertGeminiResponseToClaudeNonStream(_ context.Context, _ string, origina
 	parts := root.Get("candidates.0.content.parts")
 	textBuilder := strings.Builder{}
 	thinkingBuilder := strings.Builder{}
+	var thinkingSignature string
 	toolIDCounter := 0
 	hasToolCall := false
 	var blocks [][]byte
@@ -319,19 +320,39 @@ func ConvertGeminiResponseToClaudeNonStream(_ context.Context, _ string, origina
 	}
 
 	flushThinking := func() {
-		if thinkingBuilder.Len() == 0 {
+		if thinkingBuilder.Len() == 0 && thinkingSignature == "" {
 			return
 		}
 		block := []byte(`{"type":"thinking","thinking":""}`)
 		block, _ = sjson.SetBytes(block, "thinking", thinkingBuilder.String())
+		if thinkingSignature != "" {
+			block, _ = sjson.SetBytes(block, "signature", thinkingSignature)
+		}
 		blocks = append(blocks, block)
 		thinkingBuilder.Reset()
+		thinkingSignature = ""
 	}
 
 	if parts.IsArray() {
 		for _, part := range parts.Array() {
-			if text := part.Get("text"); text.Exists() && text.String() != "" {
-				if part.Get("thought").Bool() {
+			thoughtSignatureResult := part.Get("thoughtSignature")
+			if !thoughtSignatureResult.Exists() {
+				thoughtSignatureResult = part.Get("thought_signature")
+			}
+			hasThoughtSignature := thoughtSignatureResult.Exists() && thoughtSignatureResult.String() != ""
+			if hasThoughtSignature {
+				thinkingSignature = thoughtSignatureResult.String()
+			}
+
+			text := part.Get("text")
+			functionCall := part.Get("functionCall")
+
+			if hasThoughtSignature && (!text.Exists() || text.String() == "") && !functionCall.Exists() {
+				continue
+			}
+
+			if text.Exists() && text.String() != "" {
+				if part.Get("thought").Bool() || hasThoughtSignature {
 					flushText()
 					thinkingBuilder.WriteString(text.String())
 					continue
@@ -341,7 +362,7 @@ func ConvertGeminiResponseToClaudeNonStream(_ context.Context, _ string, origina
 				continue
 			}
 
-			if functionCall := part.Get("functionCall"); functionCall.Exists() {
+			if functionCall.Exists() {
 				flushThinking()
 				flushText()
 				hasToolCall = true
diff --git a/internal/translator/gemini/claude/gemini_claude_response_test.go b/internal/translator/gemini/claude/gemini_claude_response_test.go
index 3c4d43517..3a57f7914 100644
--- a/internal/translator/gemini/claude/gemini_claude_response_test.go
+++ b/internal/translator/gemini/claude/gemini_claude_response_test.go
@@ -5,6 +5,8 @@ import (
 	"context"
 	"strings"
 	"testing"
+
+	"github.com/tidwall/gjson"
 )
 
 func TestConvertGeminiResponseToClaude_SignatureOnlyPartDoesNotOpenEmptyTextBlock(t *testing.T) {
@@ -60,3 +62,143 @@ func TestConvertGeminiResponseToClaude_SignatureOnlyPartDoesNotOpenEmptyTextBloc
 		t.Fatalf("DONE chunk must still emit message_stop after final events: %s", outputText)
 	}
 }
+
+func TestConvertGeminiResponseToClaudeNonStream_PreservesThoughtSignature(t *testing.T) {
+	requestJSON := []byte(`{"model":"gemini-2.5-pro","messages":[{"role":"user","content":"hi"}]}`)
+	geminiResponse := []byte(`{
+		"candidates": [{
+			"content": {
+				"parts": [
+					{"text": "thinking step 1\n", "thought": true},
+					{"text": "thinking step 2", "thought": true, "thoughtSignature": "sig-xyz-123"},
+					{"text": "visible answer"}
+				]
+			},
+			"finishReason": "STOP"
+		}],
+		"usageMetadata": {
+			"promptTokenCount": 10,
+			"candidatesTokenCount": 5
+		},
+		"modelVersion": "gemini-2.5-pro",
+		"responseId": "resp-non-stream"
+	}`)
+
+	ctx := context.Background()
+	output := ConvertGeminiResponseToClaudeNonStream(ctx, "gemini-2.5-pro", requestJSON, requestJSON, geminiResponse, nil)
+	outputJSON := gjson.ParseBytes(output)
+
+	blocks := outputJSON.Get("content").Array()
+	if len(blocks) != 2 {
+		t.Fatalf("expected 2 content blocks (thinking + text), got %d: %s", len(blocks), string(output))
+	}
+
+	thinkingBlock := blocks[0]
+	if thinkingBlock.Get("type").String() != "thinking" {
+		t.Fatalf("expected first block to be thinking, got %s", thinkingBlock.Get("type").String())
+	}
+	if thinkingBlock.Get("thinking").String() != "thinking step 1\nthinking step 2" {
+		t.Fatalf("unexpected thinking content: %s", thinkingBlock.Get("thinking").String())
+	}
+	if thinkingBlock.Get("signature").String() != "sig-xyz-123" {
+		t.Fatalf("expected signature 'sig-xyz-123', got %q. Output: %s", thinkingBlock.Get("signature").String(), string(output))
+	}
+
+	textBlock := blocks[1]
+	if textBlock.Get("type").String() != "text" || textBlock.Get("text").String() != "visible answer" {
+		t.Fatalf("unexpected text block: %s", textBlock.Raw)
+	}
+}
+
+func TestConvertGeminiResponseToClaudeNonStream_PartWithThoughtSignatureWithoutThoughtBool(t *testing.T) {
+	requestJSON := []byte(`{"model":"gemini-2.5-pro","messages":[{"role":"user","content":"hi"}]}`)
+	geminiResponse := []byte(`{
+		"candidates": [{
+			"content": {
+				"parts": [
+					{"text": "inferred reasoning", "thought_signature": "sig-snake-case"},
+					{"text": "final answer"}
+				]
+			},
+			"finishReason": "STOP"
+		}],
+		"usageMetadata": {
+			"promptTokenCount": 10,
+			"candidatesTokenCount": 5
+		},
+		"modelVersion": "gemini-2.5-pro",
+		"responseId": "resp-non-stream-2"
+	}`)
+
+	ctx := context.Background()
+	output := ConvertGeminiResponseToClaudeNonStream(ctx, "gemini-2.5-pro", requestJSON, requestJSON, geminiResponse, nil)
+	outputJSON := gjson.ParseBytes(output)
+
+	blocks := outputJSON.Get("content").Array()
+	if len(blocks) != 2 {
+		t.Fatalf("expected 2 content blocks (thinking + text), got %d: %s", len(blocks), string(output))
+	}
+
+	thinkingBlock := blocks[0]
+	if thinkingBlock.Get("type").String() != "thinking" {
+		t.Fatalf("expected first block to be thinking, got %s", thinkingBlock.Get("type").String())
+	}
+	if thinkingBlock.Get("thinking").String() != "inferred reasoning" {
+		t.Fatalf("unexpected thinking content: %s", thinkingBlock.Get("thinking").String())
+	}
+	if thinkingBlock.Get("signature").String() != "sig-snake-case" {
+		t.Fatalf("expected signature 'sig-snake-case', got %q. Output: %s", thinkingBlock.Get("signature").String(), string(output))
+	}
+
+	textBlock := blocks[1]
+	if textBlock.Get("type").String() != "text" || textBlock.Get("text").String() != "final answer" {
+		t.Fatalf("unexpected text block: %s", textBlock.Raw)
+	}
+}
+
+func TestConvertGeminiResponseToClaudeNonStream_TrailingSignatureOnlyPart(t *testing.T) {
+	requestJSON := []byte(`{"model":"gemini-2.5-pro","messages":[{"role":"user","content":"hi"}]}`)
+	geminiResponse := []byte(`{
+		"candidates": [{
+			"content": {
+				"parts": [
+					{"text": "thinking step 1\n", "thought": true},
+					{"text": "", "thoughtSignature": "sig-trailing"},
+					{"text": "visible answer"}
+				]
+			},
+			"finishReason": "STOP"
+		}],
+		"usageMetadata": {
+			"promptTokenCount": 10,
+			"candidatesTokenCount": 5
+		},
+		"modelVersion": "gemini-2.5-pro",
+		"responseId": "resp-non-stream-trailing"
+	}`)
+
+	ctx := context.Background()
+	output := ConvertGeminiResponseToClaudeNonStream(ctx, "gemini-2.5-pro", requestJSON, requestJSON, geminiResponse, nil)
+	outputJSON := gjson.ParseBytes(output)
+
+	blocks := outputJSON.Get("content").Array()
+	if len(blocks) != 2 {
+		t.Fatalf("expected 2 content blocks (thinking + text), got %d: %s", len(blocks), string(output))
+	}
+
+	thinkingBlock := blocks[0]
+	if thinkingBlock.Get("type").String() != "thinking" {
+		t.Fatalf("expected first block to be thinking, got %s", thinkingBlock.Get("type").String())
+	}
+	if thinkingBlock.Get("thinking").String() != "thinking step 1\n" {
+		t.Fatalf("unexpected thinking content: %s", thinkingBlock.Get("thinking").String())
+	}
+	if thinkingBlock.Get("signature").String() != "sig-trailing" {
+		t.Fatalf("expected signature 'sig-trailing', got %q. Output: %s", thinkingBlock.Get("signature").String(), string(output))
+	}
+
+	textBlock := blocks[1]
+	if textBlock.Get("type").String() != "text" || textBlock.Get("text").String() != "visible answer" {
+		t.Fatalf("unexpected text block: %s", textBlock.Raw)
+	}
+}