diff --git a/internal/httpapi/claude/handler_messages.go b/internal/httpapi/claude/handler_messages.go
index e424503..ad8f54e 100644
--- a/internal/httpapi/claude/handler_messages.go
+++ b/internal/httpapi/claude/handler_messages.go
@@ -52,7 +52,7 @@ func (h *Handler) proxyViaOpenAI(w http.ResponseWriter, r *http.Request, store C
 		}
 	}
 	translatedReq := translatorcliproxy.ToOpenAI(sdktranslator.FormatClaude, translateModel, raw, stream)
-	translatedReq = applyClaudeThinkingPolicyToOpenAIRequest(translatedReq, req)
+	translatedReq, exposeThinking := applyClaudeThinkingPolicyToOpenAIRequest(translatedReq, req, stream)
 
 	isVercelPrepare := strings.TrimSpace(r.URL.Query().Get("__stream_prepare")) == "1"
 	isVercelRelease := strings.TrimSpace(r.URL.Query().Get("__stream_release")) == "1"
@@ -118,23 +118,26 @@ func (h *Handler) proxyViaOpenAI(w http.ResponseWriter, r *http.Request, store C
 		return true
 	}
 	converted := translatorcliproxy.FromOpenAINonStream(sdktranslator.FormatClaude, model, raw, translatedReq, body)
+	if !exposeThinking {
+		converted = stripClaudeThinkingBlocks(converted)
+	}
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(http.StatusOK)
 	_, _ = w.Write(converted)
 	return true
 }
 
-func applyClaudeThinkingPolicyToOpenAIRequest(translated []byte, original map[string]any) []byte {
+func applyClaudeThinkingPolicyToOpenAIRequest(translated []byte, original map[string]any, stream bool) ([]byte, bool) {
 	req := map[string]any{}
 	if err := json.Unmarshal(translated, &req); err != nil {
-		return translated
+		return translated, false
 	}
 	enabled, ok := util.ResolveThinkingOverride(original)
 	if !ok {
 		if _, translatedHasOverride := util.ResolveThinkingOverride(req); translatedHasOverride {
-			return translated
+			return translated, false
 		}
-		enabled = false
+		enabled = !stream
 	}
 	typ := "disabled"
 	if enabled {
@@ -143,7 +146,33 @@ func applyClaudeThinkingPolicyToOpenAIRequest(translated []byte, original map[st
 	req["thinking"] = map[string]any{"type": typ}
 	out, err := json.Marshal(req)
 	if err != nil {
-		return translated
+		return translated, ok && enabled
+	}
+	return out, ok && enabled
+}
+
+func stripClaudeThinkingBlocks(raw []byte) []byte {
+	var payload map[string]any
+	if err := json.Unmarshal(raw, &payload); err != nil {
+		return raw
+	}
+	content, _ := payload["content"].([]any)
+	if len(content) == 0 {
+		return raw
+	}
+	filtered := make([]any, 0, len(content))
+	for _, item := range content {
+		block, _ := item.(map[string]any)
+		blockType, _ := block["type"].(string)
+		if strings.TrimSpace(blockType) == "thinking" {
+			continue
+		}
+		filtered = append(filtered, item)
+	}
+	payload["content"] = filtered
+	out, err := json.Marshal(payload)
+	if err != nil {
+		return raw
 	}
 	return out
 }
diff --git a/internal/httpapi/claude/proxy_vercel_test.go b/internal/httpapi/claude/proxy_vercel_test.go
index 2eff38b..a8a9cd4 100644
--- a/internal/httpapi/claude/proxy_vercel_test.go
+++ b/internal/httpapi/claude/proxy_vercel_test.go
@@ -126,7 +126,7 @@ func TestClaudeProxyViaOpenAIPreservesThinkingOverride(t *testing.T) {
 	}
 }
 
-func TestClaudeProxyViaOpenAIDisablesThinkingByDefault(t *testing.T) {
+func TestClaudeProxyViaOpenAIEnablesThinkingInternallyByDefaultForNonStream(t *testing.T) {
 	openAI := &openAIProxyCaptureStub{}
 	h := &Handler{
 		Store:  claudeProxyStoreStub{aliases: map[string]string{"claude-sonnet-4-6": "deepseek-v4-flash"}},
@@ -141,8 +141,8 @@ func TestClaudeProxyViaOpenAIDisablesThinkingByDefault(t *testing.T) {
 		t.Fatalf("unexpected status: %d body=%s", rec.Code, rec.Body.String())
 	}
 	thinking, _ := openAI.seenReq["thinking"].(map[string]any)
-	if thinking["type"] != "disabled" {
-		t.Fatalf("expected Claude default to disable downstream thinking, got %#v", openAI.seenReq)
+	if thinking["type"] != "enabled" {
+		t.Fatalf("expected Claude non-stream default to enable downstream thinking internally, got %#v", openAI.seenReq)
 	}
 }
 
@@ -166,6 +166,43 @@ func TestClaudeProxyViaOpenAIEnablesThinkingWhenRequested(t *testing.T) {
 	}
 }
 
+func TestClaudeProxyViaOpenAIKeepsStreamDefaultThinkingDisabled(t *testing.T) {
+	openAI := &openAIProxyCaptureStub{}
+	h := &Handler{
+		Store:  claudeProxyStoreStub{aliases: map[string]string{"claude-sonnet-4-6": "deepseek-v4-flash"}},
+		OpenAI: openAI,
+	}
+	req := httptest.NewRequest(http.MethodPost, "/anthropic/v1/messages", strings.NewReader(`{"model":"claude-sonnet-4-6","messages":[{"role":"user","content":"hi"}],"stream":true}`))
+	rec := httptest.NewRecorder()
+
+	h.Messages(rec, req)
+
+	thinking, _ := openAI.seenReq["thinking"].(map[string]any)
+	if thinking["type"] != "disabled" {
+		t.Fatalf("expected Claude stream default to keep downstream thinking disabled, got %#v", openAI.seenReq)
+	}
+}
+
+func TestClaudeProxyViaOpenAIStripsThinkingBlocksFromNonStreamResponse(t *testing.T) {
+	body := `{"id":"chatcmpl_1","object":"chat.completion","created":1,"model":"claude-sonnet-4-5","choices":[{"index":0,"message":{"role":"assistant","content":null,"reasoning_content":"internal reasoning","tool_calls":[{"id":"call_1","type":"function","function":{"name":"search","arguments":"{\"q\":\"x\"}"}}]},"finish_reason":"tool_calls"}],"usage":{"prompt_tokens":1,"completion_tokens":1,"total_tokens":2}}`
+	h := &Handler{OpenAI: openAIProxyStub{status: 200, body: body}}
+	req := httptest.NewRequest(http.MethodPost, "/anthropic/v1/messages", strings.NewReader(`{"model":"claude-sonnet-4-5","messages":[{"role":"user","content":"hi"}],"stream":false}`))
+	rec := httptest.NewRecorder()
+
+	h.Messages(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("unexpected status: %d body=%s", rec.Code, rec.Body.String())
+	}
+	got := rec.Body.String()
+	if strings.Contains(got, `"type":"thinking"`) {
+		t.Fatalf("expected converted Claude response to strip thinking block, got %s", got)
+	}
+	if !strings.Contains(got, `"tool_use"`) {
+		t.Fatalf("expected converted Claude response to preserve tool_use, got %s", got)
+	}
+}
+
 func TestClaudeProxyTranslatesInlineImageToOpenAIDataURL(t *testing.T) {
 	openAI := &openAIProxyCaptureStub{}
 	h := &Handler{OpenAI: openAI}