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 47b9b321c..c70451e4a 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)}
@@ -283,7 +284,7 @@ func interactionsStepDeltaToResponses(root gjson.Result, st *interactionsToRespo
 		return [][]byte{emitResponsesEvent("response.reasoning_summary_text.delta", payload)}
 	case "thought_signature":
 		if signature := delta.Get("signature").String(); signature != "" {
-			st.ReasoningEncrypted[index] = signature
+			st.ReasoningEncrypted[index] = interactionsReasoningEncryptedContent(signature)
 		}
 		return nil
 	case "arguments_delta":
@@ -403,6 +404,16 @@ func responsesCompletedEvent(modelName string, root gjson.Result, st *interactio
 	return emitResponsesEvent("response.completed", payload)
 }
 
+func interactionsReasoningEncryptedContent(raw string) string {
+	if raw == "" {
+		return ""
+	}
+	if _, err := signature.InspectGPTReasoningSignature(raw); err != nil {
+		return ""
+	}
+	return raw
+}
+
 func interactionsThoughtSignature(step gjson.Result) string {
 	for _, path := range []string{
 		"encrypted_content",
@@ -411,23 +422,25 @@ func interactionsThoughtSignature(step gjson.Result) string {
 		"thoughtSignature",
 		"extra_content.google.thought_signature",
 	} {
-		if signature := step.Get(path).String(); signature != "" {
-			return signature
+		if raw := step.Get(path).String(); raw != "" {
+			if enc := interactionsReasoningEncryptedContent(raw); enc != "" {
+				return enc
+			}
 		}
 	}
 	content := step.Get("content")
 	if content.IsArray() {
-		var signature string
+		var raw string
 		content.ForEach(func(_, part gjson.Result) bool {
-			signature = firstNonEmpty(
+			raw = firstNonEmpty(
 				part.Get("signature").String(),
 				part.Get("thought_signature").String(),
 				part.Get("thoughtSignature").String(),
 				part.Get("extra_content.google.thought_signature").String(),
 			)
-			return signature == ""
+			return raw == ""
 		})
-		return signature
+		return interactionsReasoningEncryptedContent(raw)
 	}
 	return ""
 }
@@ -510,7 +523,7 @@ 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 e79c11cbc..8352bb7a7 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 +224,18 @@ data: {"index":0,"event_type":"step.stop"}
 	}
 }
 
+func testGPTReasoningSignatureForInteractions() string {
+	payload := make([]byte, 1+8+16+16+32)
+	payload[0] = 0x80
+	for i := 9; i < len(payload); i++ {
+		payload[i] = byte(i)
+	}
+	return base64.RawURLEncoding.EncodeToString(payload)
+}
+
 func TestConvertInteractionsResponseToOpenAIResponsesStreamPreservesThoughtSignature(t *testing.T) {
 	var param any
-	signature := "EtoRtestThoughtSignature"
+	signature := testGPTReasoningSignatureForInteractions()
 	var out [][]byte
 	for _, raw := range [][]byte{
 		[]byte(`event: step.start
@@ -272,6 +282,48 @@ data: {"interaction":{"id":"interaction_1","status":"completed","object":"intera
 	}
 }
 
+func TestConvertInteractionsResponseToOpenAIResponsesStreamDropsInvalidThoughtSignature(t *testing.T) {
+	var param any
+	signature := "foreign-thought-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":"` + signature + `","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 gjson.GetBytes(donePayload, "item.encrypted_content").Exists() && gjson.GetBytes(donePayload, "item.encrypted_content").String() != "" {
+		t.Fatalf("invalid encrypted_content should be dropped, got %s", 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 gjson.GetBytes(completedPayload, "response.output.0.encrypted_content").Exists() && gjson.GetBytes(completedPayload, "response.output.0.encrypted_content").String() != "" {
+		t.Fatalf("completed invalid encrypted_content should be dropped, got %s", string(completedPayload))
+	}
+}
+
 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)