diff --git a/internal/translator/openai/interactions/responses/interactions_openai_responses_response.go b/internal/translator/openai/interactions/responses/interactions_openai_responses_response.go
index 47b9b321..5a9f7808 100644
--- a/internal/translator/openai/interactions/responses/interactions_openai_responses_response.go
+++ b/internal/translator/openai/interactions/responses/interactions_openai_responses_response.go
@@ -7,6 +7,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	translatorcommon "github.com/router-for-me/CLIProxyAPI/v7/internal/translator/common"
 	"github.com/tidwall/gjson"
 	"github.com/tidwall/sjson"
@@ -237,7 +238,7 @@ func interactionsStepStartToResponses(root gjson.Result, st *interactionsToRespo
 		added, _ = sjson.SetBytes(added, "sequence_number", nextResponsesSeq(st))
 		added, _ = sjson.SetBytes(added, "output_index", index)
 		added, _ = sjson.SetBytes(added, "item.id", itemID)
-		if signature := st.ReasoningEncrypted[index]; signature != "" {
+		if signature := interactionsReasoningEncryptedContent(st.ReasoningEncrypted[index]); signature != "" {
 			added, _ = sjson.SetBytes(added, "item.encrypted_content", signature)
 		}
 		return [][]byte{emitResponsesEvent("response.output_item.added", added)}
@@ -282,7 +283,7 @@ func interactionsStepDeltaToResponses(root gjson.Result, st *interactionsToRespo
 		payload, _ = sjson.SetBytes(payload, "delta", text)
 		return [][]byte{emitResponsesEvent("response.reasoning_summary_text.delta", payload)}
 	case "thought_signature":
-		if signature := delta.Get("signature").String(); signature != "" {
+		if signature := interactionsReasoningEncryptedContent(delta.Get("signature").String()); signature != "" {
 			st.ReasoningEncrypted[index] = signature
 		}
 		return nil
@@ -411,7 +412,7 @@ func interactionsThoughtSignature(step gjson.Result) string {
 		"thoughtSignature",
 		"extra_content.google.thought_signature",
 	} {
-		if signature := step.Get(path).String(); signature != "" {
+		if signature := interactionsReasoningEncryptedContent(step.Get(path).String()); signature != "" {
 			return signature
 		}
 	}
@@ -419,19 +420,34 @@ func interactionsThoughtSignature(step gjson.Result) string {
 	if content.IsArray() {
 		var signature string
 		content.ForEach(func(_, part gjson.Result) bool {
-			signature = firstNonEmpty(
+			candidate := firstNonEmpty(
 				part.Get("signature").String(),
 				part.Get("thought_signature").String(),
 				part.Get("thoughtSignature").String(),
 				part.Get("extra_content.google.thought_signature").String(),
 			)
-			return signature == ""
+			if valid := interactionsReasoningEncryptedContent(candidate); valid != "" {
+				signature = valid
+				return false
+			}
+			return true
 		})
 		return signature
 	}
 	return ""
 }
 
+func interactionsReasoningEncryptedContent(rawSignature string) string {
+	candidate := strings.TrimSpace(rawSignature)
+	if candidate == "" {
+		return ""
+	}
+	if _, err := signature.InspectGPTReasoningSignature(candidate); err != nil {
+		return ""
+	}
+	return candidate
+}
+
 func recordResponsesReasoningSummary(st *interactionsToResponsesStreamState, index int, text string) {
 	if text == "" {
 		return
@@ -510,7 +526,7 @@ func responsesCompletedOutputItem(index int, itemType string, st *interactionsTo
 func responsesReasoningItem(index int, st *interactionsToResponsesStreamState) []byte {
 	item := []byte(`{"id":"","type":"reasoning","encrypted_content":"","summary":[]}`)
 	item, _ = sjson.SetBytes(item, "id", st.ItemIDs[index])
-	if signature := st.ReasoningEncrypted[index]; signature != "" {
+	if signature := interactionsReasoningEncryptedContent(st.ReasoningEncrypted[index]); signature != "" {
 		item, _ = sjson.SetBytes(item, "encrypted_content", signature)
 	}
 	summaries := st.ReasoningSummaries[index]
diff --git a/internal/translator/openai/interactions/responses/interactions_openai_responses_response_test.go b/internal/translator/openai/interactions/responses/interactions_openai_responses_response_test.go
index e79c11cb..5e6946fe 100644
--- a/internal/translator/openai/interactions/responses/interactions_openai_responses_response_test.go
+++ b/internal/translator/openai/interactions/responses/interactions_openai_responses_response_test.go
@@ -3,6 +3,7 @@ package responses
 import (
 	"bytes"
 	"context"
+	"encoding/base64"
 	"strings"
 	"testing"
 
@@ -223,9 +224,19 @@ data: {"index":0,"event_type":"step.stop"}
 	}
 }
 
+func testGPTResponsesReasoningSignature() string {
+	payload := make([]byte, 1+8+16+16+32)
+	payload[0] = 0x80
+	payload[8] = 1
+	for i := 9; i < len(payload); i++ {
+		payload[i] = byte(i)
+	}
+	return base64.URLEncoding.EncodeToString(payload)
+}
+
 func TestConvertInteractionsResponseToOpenAIResponsesStreamPreservesThoughtSignature(t *testing.T) {
 	var param any
-	signature := "EtoRtestThoughtSignature"
+	signature := testGPTResponsesReasoningSignature()
 	var out [][]byte
 	for _, raw := range [][]byte{
 		[]byte(`event: step.start
@@ -272,6 +283,69 @@ data: {"interaction":{"id":"interaction_1","status":"completed","object":"intera
 	}
 }
 
+func TestConvertInteractionsResponseToOpenAIResponsesStreamDropsForeignThoughtSignature(t *testing.T) {
+	var param any
+	foreignSignature := "foreign-gemini-signature"
+	var out [][]byte
+	for _, raw := range [][]byte{
+		[]byte(`event: step.start
+data: {"index":0,"step":{"type":"thought"},"event_type":"step.start"}
+
+`),
+		[]byte(`event: step.delta
+data: {"index":0,"delta":{"content":{"text":"thinking","type":"text"},"type":"thought_summary"},"event_type":"step.delta"}
+
+`),
+		[]byte(`event: step.delta
+data: {"index":0,"delta":{"signature":"` + foreignSignature + `","type":"thought_signature"},"event_type":"step.delta"}
+
+`),
+		[]byte(`event: step.stop
+data: {"index":0,"event_type":"step.stop"}
+
+`),
+		[]byte(`event: interaction.completed
+data: {"interaction":{"id":"interaction_1","status":"completed","object":"interaction","model":"gpt-test"},"event_type":"interaction.completed"}
+
+`),
+	} {
+		out = append(out, ConvertInteractionsResponseToOpenAIResponses(context.Background(), "gpt-test", []byte(`{"model":"gpt-test"}`), nil, raw, &param)...)
+	}
+
+	donePayload := findResponsesEventPayload(out, "response.output_item.done")
+	if got := gjson.GetBytes(donePayload, "item.encrypted_content").String(); got != "" {
+		t.Fatalf("done encrypted_content = %q, want empty for foreign signature. Payload: %s", got, string(donePayload))
+	}
+	if got := gjson.GetBytes(donePayload, "item.summary.0.text").String(); got != "thinking" {
+		t.Fatalf("done summary = %q, want thinking. Payload: %s", got, string(donePayload))
+	}
+	completedPayload := findResponsesEventPayload(out, "response.completed")
+	if got := gjson.GetBytes(completedPayload, "response.output.0.encrypted_content").String(); got != "" {
+		t.Fatalf("completed encrypted_content = %q, want empty for foreign signature. Payload: %s", got, string(completedPayload))
+	}
+}
+
+func TestConvertInteractionsResponseToOpenAIResponsesNonStreamThoughtSignature(t *testing.T) {
+	validSig := testGPTResponsesReasoningSignature()
+	rawValid := []byte(`{"id":"interaction_1","object":"interaction","status":"completed","steps":[{"type":"thought","signature":"` + validSig + `","content":[{"type":"text","text":"thinking"}]}],"usage":{"total_tokens":1}}`)
+	outValid := ConvertInteractionsResponseToOpenAIResponsesNonStream(context.Background(), "gpt-test", []byte(`{"model":"gpt-test"}`), nil, rawValid, nil)
+	if got := gjson.GetBytes(outValid, "output.0.encrypted_content").String(); got != validSig {
+		t.Fatalf("valid encrypted_content = %q, want %q. Output: %s", got, validSig, string(outValid))
+	}
+	if got := gjson.GetBytes(outValid, "output.0.summary.0.text").String(); got != "thinking" {
+		t.Fatalf("summary = %q, want thinking. Output: %s", got, string(outValid))
+	}
+
+	rawForeign := []byte(`{"id":"interaction_1","object":"interaction","status":"completed","steps":[{"type":"thought","thought_signature":"foreign-gemini-signature","content":[{"type":"text","text":"thinking"}]}],"usage":{"total_tokens":1}}`)
+	outForeign := ConvertInteractionsResponseToOpenAIResponsesNonStream(context.Background(), "gpt-test", []byte(`{"model":"gpt-test"}`), nil, rawForeign, nil)
+	if got := gjson.GetBytes(outForeign, "output.0.encrypted_content").String(); got != "" {
+		t.Fatalf("foreign encrypted_content = %q, want empty. Output: %s", got, string(outForeign))
+	}
+	if got := gjson.GetBytes(outForeign, "output.0.summary.0.text").String(); got != "thinking" {
+		t.Fatalf("summary = %q, want thinking. Output: %s", got, string(outForeign))
+	}
+}
+
 func TestConvertOpenAIResponsesResponseToInteractionsNonStreamFunctionCall(t *testing.T) {
 	raw := []byte(`{"id":"resp_1","output":[{"type":"function_call","name":"lookup","call_id":"call_1","arguments":{"q":"x"}}],"usage":{"input_tokens":1,"output_tokens":2,"total_tokens":3}}`)
 	out := ConvertOpenAIResponsesResponseToInteractionsNonStream(context.Background(), "gpt-test", nil, nil, raw, nil)