diff --git a/relay/channel/claude/relay-claude.go b/relay/channel/claude/relay-claude.go
index d4b4fbe..361b387 100644
--- a/relay/channel/claude/relay-claude.go
+++ b/relay/channel/claude/relay-claude.go
@@ -778,14 +778,21 @@ func ClaudeStreamHandler(c *gin.Context, resp *http.Response, info *relaycommon.
 		Usage:        &dto.Usage{},
 	}
 	var err *types.NewAPIError
+	var normalStreamStarted bool
 	helper.StreamScannerHandler(c, resp, info, func(data string) bool {
 		err = HandleStreamResponseData(c, info, claudeInfo, data)
 		if err != nil {
+			if normalStreamStarted || helper.StreamDataWritten(c) {
+				logger.LogError(c, "upstream claude stream error after normal stream started: "+err.Error())
+				err = nil
+			}
 			return false
 		}
+		normalStreamStarted = true
 		return true
 	})
 	if err != nil {
+		helper.ClearEventStreamHeadersIfNotWritten(c)
 		return nil, err
 	}
 
diff --git a/relay/channel/claude/relay_claude_test.go b/relay/channel/claude/relay_claude_test.go
index e34c861..f949113 100644
--- a/relay/channel/claude/relay_claude_test.go
+++ b/relay/channel/claude/relay_claude_test.go
@@ -1,10 +1,18 @@
 package claude
 
 import (
+	"io"
+	"net/http"
+	"net/http/httptest"
 	"strings"
 	"testing"
 
+	"github.com/QuantumNous/new-api/constant"
 	"github.com/QuantumNous/new-api/dto"
+	relaycommon "github.com/QuantumNous/new-api/relay/common"
+	"github.com/QuantumNous/new-api/types"
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
 )
 
 func TestFormatClaudeResponseInfo_MessageStart(t *testing.T) {
@@ -173,3 +181,65 @@ func TestFormatClaudeResponseInfo_ContentBlockDelta(t *testing.T) {
 		t.Errorf("ResponseText = %q, want %q", claudeInfo.ResponseText.String(), "hello")
 	}
 }
+
+func TestClaudeStreamHandlerReturnsErrorOnInitialErrorEvent(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	oldTimeout := constant.StreamingTimeout
+	constant.StreamingTimeout = 30
+	t.Cleanup(func() {
+		constant.StreamingTimeout = oldTimeout
+	})
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/messages", nil)
+
+	errorEvent := `{"type":"error","error":{"type":"overloaded_error","message":"Overloaded"}}`
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(strings.NewReader("data: " + errorEvent + "\n\n")),
+	}
+	info := &relaycommon.RelayInfo{
+		RelayFormat: types.RelayFormatClaude,
+		ChannelMeta: &relaycommon.ChannelMeta{
+			UpstreamModelName: "claude-test",
+		},
+	}
+
+	usage, err := ClaudeStreamHandler(c, resp, info)
+	require.Nil(t, usage)
+	require.Error(t, err)
+	require.Empty(t, w.Body.String())
+}
+
+func TestClaudeStreamHandlerDoesNotRetryAfterNormalStreamData(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	oldTimeout := constant.StreamingTimeout
+	constant.StreamingTimeout = 30
+	t.Cleanup(func() {
+		constant.StreamingTimeout = oldTimeout
+	})
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/messages", nil)
+
+	normalEvent := `{"type":"message_start","message":{"id":"msg_test","model":"claude-test","usage":{"input_tokens":1,"output_tokens":1}}}`
+	errorEvent := `{"type":"error","error":{"type":"overloaded_error","message":"Overloaded"}}`
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(strings.NewReader("data: " + normalEvent + "\n\ndata: " + errorEvent + "\n\n")),
+	}
+	info := &relaycommon.RelayInfo{
+		RelayFormat: types.RelayFormatClaude,
+		ChannelMeta: &relaycommon.ChannelMeta{
+			UpstreamModelName: "claude-test",
+		},
+	}
+
+	usage, err := ClaudeStreamHandler(c, resp, info)
+	require.Nil(t, err)
+	require.NotNil(t, usage)
+	require.Contains(t, w.Body.String(), "message_start")
+	require.NotContains(t, w.Body.String(), "overloaded_error")
+}
diff --git a/relay/channel/gemini/relay-gemini.go b/relay/channel/gemini/relay-gemini.go
index 66f794a..3bc06e0 100644
--- a/relay/channel/gemini/relay-gemini.go
+++ b/relay/channel/gemini/relay-gemini.go
@@ -1286,6 +1286,7 @@ func geminiStreamHandler(c *gin.Context, info *relaycommon.RelayInfo, resp *http
 	var imageCount int
 	responseText := strings.Builder{}
 	var streamErr *types.NewAPIError
+	var normalStreamStarted bool
 
 	helper.StreamScannerHandler(c, resp, info, func(data string) bool {
 		var geminiResponse dto.GeminiChatResponse
@@ -1297,15 +1298,21 @@ func geminiStreamHandler(c *gin.Context, info *relaycommon.RelayInfo, resp *http
 
 		if len(geminiResponse.Candidates) == 0 && geminiResponse.PromptFeedback != nil && geminiResponse.PromptFeedback.BlockReason != nil {
 			common.SetContextKey(c, constant.ContextKeyAdminRejectReason, fmt.Sprintf("gemini_block_reason=%s", *geminiResponse.PromptFeedback.BlockReason))
-			streamErr = types.NewOpenAIError(
+			apiErr := types.NewOpenAIError(
 				errors.New("request blocked by Gemini API: "+*geminiResponse.PromptFeedback.BlockReason),
 				types.ErrorCodePromptBlocked,
 				http.StatusBadRequest,
 			)
-			streamErr.UpstreamBody = service.TruncateBody(data)
+			apiErr.UpstreamBody = service.TruncateBody(data)
+			if !normalStreamStarted && !helper.StreamDataWritten(c) {
+				streamErr = apiErr
+			} else {
+				logger.LogError(c, "upstream gemini stream blocked after normal stream started: "+apiErr.Error())
+			}
 			return false
 		}
 
+		normalStreamStarted = true
 		// 统计图片数量
 		for _, candidate := range geminiResponse.Candidates {
 			for _, part := range candidate.Content.Parts {
diff --git a/relay/channel/gemini/relay_gemini_usage_test.go b/relay/channel/gemini/relay_gemini_usage_test.go
index 7d111bc..021e3af 100644
--- a/relay/channel/gemini/relay_gemini_usage_test.go
+++ b/relay/channel/gemini/relay_gemini_usage_test.go
@@ -328,6 +328,65 @@ func TestGeminiStreamHandlerReturnsErrorOnPromptBlock(t *testing.T) {
 	require.Contains(t, newAPIError.UpstreamBody, "SAFETY")
 }
 
+func TestGeminiStreamHandlerDoesNotRetryAfterNormalStreamData(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	oldStreamingTimeout := constant.StreamingTimeout
+	constant.StreamingTimeout = 300
+	t.Cleanup(func() {
+		constant.StreamingTimeout = oldStreamingTimeout
+	})
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)
+
+	normalChunk := dto.GeminiChatResponse{
+		Candidates: []dto.GeminiChatCandidate{
+			{
+				Content: dto.GeminiChatContent{
+					Role: "model",
+					Parts: []dto.GeminiPart{
+						{Text: "partial"},
+					},
+				},
+			},
+		},
+	}
+	blockReason := "SAFETY"
+	blockChunk := dto.GeminiChatResponse{
+		PromptFeedback: &dto.GeminiChatPromptFeedback{
+			BlockReason: &blockReason,
+		},
+	}
+
+	normalData, err := common.Marshal(normalChunk)
+	require.NoError(t, err)
+	blockData, err := common.Marshal(blockChunk)
+	require.NoError(t, err)
+
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(bytes.NewReader([]byte("data: " + string(normalData) + "\n\ndata: " + string(blockData) + "\n\n"))),
+	}
+	info := &relaycommon.RelayInfo{
+		RelayFormat: types.RelayFormatOpenAI,
+		ChannelMeta: &relaycommon.ChannelMeta{
+			UpstreamModelName: "gemini-test",
+		},
+	}
+
+	called := false
+	usage, newAPIError := geminiStreamHandler(c, info, resp, func(_ string, _ *dto.GeminiChatResponse) bool {
+		called = true
+		return true
+	})
+
+	require.Nil(t, newAPIError)
+	require.NotNil(t, usage)
+	require.True(t, called)
+	require.Empty(t, w.Body.String())
+}
+
 func TestGeminiTextGenerationHandlerUsesEstimatedPromptTokensWhenUsagePromptMissing(t *testing.T) {
 	t.Parallel()
 
diff --git a/relay/channel/openai/helper.go b/relay/channel/openai/helper.go
index 30abee6..f195899 100644
--- a/relay/channel/openai/helper.go
+++ b/relay/channel/openai/helper.go
@@ -29,7 +29,7 @@ func streamOpenAIErrorFromData(data string, statusCode int) *types.NewAPIError {
 	if openaiErr == nil {
 		return nil
 	}
-	if statusCode < 100 || statusCode > 599 {
+	if statusCode < 100 || statusCode > 599 || (statusCode >= 200 && statusCode < 300) {
 		statusCode = http.StatusInternalServerError
 	}
 	apiErr := types.WithOpenAIError(*openaiErr, statusCode)
diff --git a/relay/channel/openai/relay-openai.go b/relay/channel/openai/relay-openai.go
index d20934c..e5c0a76 100644
--- a/relay/channel/openai/relay-openai.go
+++ b/relay/channel/openai/relay-openai.go
@@ -122,6 +122,7 @@ func OaiStreamHandler(c *gin.Context, info *relaycommon.RelayInfo, resp *http.Re
 	var streamItems []string // store stream items
 	var lastStreamData string
 	var streamErr *types.NewAPIError
+	var normalStreamStarted bool
 	var secondLastStreamData string // 存储倒数第二个stream data，用于音频模型
 
 	// 检查是否为音频模型
@@ -129,14 +130,15 @@ func OaiStreamHandler(c *gin.Context, info *relaycommon.RelayInfo, resp *http.Re
 
 	helper.StreamScannerHandler(c, resp, info, func(data string) bool {
 		if apiErr := streamOpenAIErrorFromData(data, resp.StatusCode); apiErr != nil {
-			if !c.Writer.Written() {
+			if !normalStreamStarted && !helper.StreamDataWritten(c) {
 				streamErr = apiErr
 			} else {
-				logger.LogError(c, "upstream stream error after downstream response was written: "+apiErr.Error())
+				logger.LogError(c, "upstream stream error after normal stream started: "+apiErr.Error())
 			}
 			return false
 		}
 
+		normalStreamStarted = true
 		if lastStreamData != "" {
 			err := HandleStreamFormat(c, info, lastStreamData, info.ChannelSetting.ForceFormat, info.ChannelSetting.ThinkingToContent)
 			if err != nil {
diff --git a/relay/channel/openai/relay_responses.go b/relay/channel/openai/relay_responses.go
index e5fed78..a3b1f82 100644
--- a/relay/channel/openai/relay_responses.go
+++ b/relay/channel/openai/relay_responses.go
@@ -85,6 +85,7 @@ func OaiResponsesStreamHandler(c *gin.Context, info *relaycommon.RelayInfo, resp
 	var usage = &dto.Usage{}
 	var responseTextBuilder strings.Builder
 	var streamErr *types.NewAPIError
+	var normalStreamStarted bool
 
 	helper.StreamScannerHandler(c, resp, info, func(data string) bool {
 
@@ -92,10 +93,16 @@ func OaiResponsesStreamHandler(c *gin.Context, info *relaycommon.RelayInfo, resp
 		if err := common.UnmarshalJsonStr(data, &streamResponse); err == nil {
 			switch streamResponse.Type {
 			case "response.error", "response.failed", "error":
-				streamErr = handleResponsesStreamError(streamResponse, data)
+				apiErr := handleResponsesStreamError(streamResponse, data)
+				if !normalStreamStarted && !helper.StreamDataWritten(c) {
+					streamErr = apiErr
+				} else if apiErr != nil {
+					logger.LogError(c, "upstream responses stream error after normal stream started: "+apiErr.Error())
+				}
 				return false
 			}
 
+			normalStreamStarted = true
 			sendResponsesStreamData(c, streamResponse, data)
 			switch streamResponse.Type {
 			case "response.completed":
diff --git a/relay/channel/openai/upstream_body_test.go b/relay/channel/openai/upstream_body_test.go
index a91c82c..3054ecc 100644
--- a/relay/channel/openai/upstream_body_test.go
+++ b/relay/channel/openai/upstream_body_test.go
@@ -11,6 +11,7 @@ import (
 	"github.com/QuantumNous/new-api/constant"
 	"github.com/QuantumNous/new-api/dto"
 	relaycommon "github.com/QuantumNous/new-api/relay/common"
+	"github.com/QuantumNous/new-api/relay/helper"
 	"github.com/QuantumNous/new-api/types"
 	"github.com/gin-gonic/gin"
 	"github.com/stretchr/testify/assert"
@@ -109,6 +110,7 @@ func TestOaiResponsesStreamHandlerDoesNotForwardErrorEvent(t *testing.T) {
 	usage, err := OaiResponsesStreamHandler(c, &relaycommon.RelayInfo{}, resp)
 	require.Nil(t, usage)
 	require.Error(t, err)
+	assert.Equal(t, http.StatusInternalServerError, err.StatusCode)
 	assert.Contains(t, err.UpstreamBody, "rate_limit_exceeded")
 	assert.NotContains(t, w.Body.String(), "rate_limit_exceeded")
 	assert.Empty(t, w.Body.String())
@@ -148,6 +150,104 @@ func TestOaiStreamHandlerDoesNotForwardInitialErrorEvent(t *testing.T) {
 	assert.Empty(t, w.Header().Get("Content-Type"))
 }
 
+func TestOaiStreamHandlerReturnsInitialErrorAfterPing(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	oldTimeout := constant.StreamingTimeout
+	constant.StreamingTimeout = 30
+	t.Cleanup(func() {
+		constant.StreamingTimeout = oldTimeout
+	})
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)
+
+	require.NoError(t, helper.PingData(c))
+
+	errorEvent := `{"error":{"type":"tokens","code":"rate_limit_exceeded","message":"Request too large","param":null}}`
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(strings.NewReader("data: " + errorEvent + "\n\n")),
+	}
+	info := &relaycommon.RelayInfo{
+		RelayFormat: types.RelayFormatOpenAI,
+		ChannelMeta: &relaycommon.ChannelMeta{
+			UpstreamModelName: "gpt-test",
+		},
+	}
+
+	usage, err := OaiStreamHandler(c, info, resp)
+	require.Nil(t, usage)
+	require.Error(t, err)
+	assert.Equal(t, http.StatusInternalServerError, err.StatusCode)
+	assert.Contains(t, err.UpstreamBody, "rate_limit_exceeded")
+	assert.Contains(t, w.Body.String(), ": PING")
+	assert.NotContains(t, w.Body.String(), "rate_limit_exceeded")
+}
+
+func TestOaiStreamHandlerDoesNotRetryAfterNormalStreamData(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	oldTimeout := constant.StreamingTimeout
+	constant.StreamingTimeout = 30
+	t.Cleanup(func() {
+		constant.StreamingTimeout = oldTimeout
+	})
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)
+
+	normalEvent := `{"id":"chatcmpl-test","object":"chat.completion.chunk","created":1,"model":"gpt-test","choices":[{"index":0,"delta":{"content":"hi"}}]}`
+	errorEvent := `{"error":{"type":"tokens","code":"rate_limit_exceeded","message":"Request too large","param":null}}`
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(strings.NewReader("data: " + normalEvent + "\n\ndata: " + errorEvent + "\n\n")),
+	}
+	info := &relaycommon.RelayInfo{
+		RelayFormat: types.RelayFormatOpenAI,
+		ChannelMeta: &relaycommon.ChannelMeta{
+			UpstreamModelName: "gpt-test",
+		},
+	}
+
+	usage, err := OaiStreamHandler(c, info, resp)
+	require.Nil(t, err)
+	require.NotNil(t, usage)
+	assert.Contains(t, w.Body.String(), "hi")
+	assert.NotContains(t, w.Body.String(), "rate_limit_exceeded")
+}
+
+func TestOaiResponsesStreamHandlerDoesNotRetryAfterNormalStreamData(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	oldTimeout := constant.StreamingTimeout
+	constant.StreamingTimeout = 30
+	t.Cleanup(func() {
+		constant.StreamingTimeout = oldTimeout
+	})
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/responses", nil)
+
+	normalEvent := `{"type":"response.completed","response":{"id":"resp_test","usage":{"input_tokens":1,"output_tokens":1,"total_tokens":2}}}`
+	errorEvent := `{"type":"error","error":{"type":"tokens","code":"rate_limit_exceeded","message":"Request too large","param":null},"sequence_number":2}`
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(strings.NewReader("data: " + normalEvent + "\n\ndata: " + errorEvent + "\n\n")),
+	}
+	info := &relaycommon.RelayInfo{
+		ChannelMeta: &relaycommon.ChannelMeta{
+			UpstreamModelName: "gpt-test",
+		},
+	}
+
+	usage, err := OaiResponsesStreamHandler(c, info, resp)
+	require.Nil(t, err)
+	require.NotNil(t, usage)
+	assert.Contains(t, w.Body.String(), "response.completed")
+	assert.NotContains(t, w.Body.String(), "rate_limit_exceeded")
+}
+
 func TestOaiResponsesToChatHandlerAttachesUpstreamBodyOnInvalidJSON(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	w := httptest.NewRecorder()
diff --git a/relay/helper/common.go b/relay/helper/common.go
index 8fffb5e..b0445e4 100644
--- a/relay/helper/common.go
+++ b/relay/helper/common.go
@@ -14,6 +14,40 @@ import (
 	"github.com/gorilla/websocket"
 )
 
+const (
+	streamBodyWrittenKey = "stream_body_written"
+	streamDataWrittenKey = "stream_data_written"
+)
+
+func MarkStreamBodyWritten(c *gin.Context) {
+	if c == nil {
+		return
+	}
+	c.Set(streamBodyWrittenKey, true)
+}
+
+func StreamBodyWritten(c *gin.Context) bool {
+	if c == nil {
+		return false
+	}
+	return c.GetBool(streamBodyWrittenKey)
+}
+
+func MarkStreamDataWritten(c *gin.Context) {
+	if c == nil {
+		return
+	}
+	MarkStreamBodyWritten(c)
+	c.Set(streamDataWrittenKey, true)
+}
+
+func StreamDataWritten(c *gin.Context) bool {
+	if c == nil {
+		return false
+	}
+	return c.GetBool(streamDataWrittenKey)
+}
+
 func FlushWriter(c *gin.Context) (err error) {
 	defer func() {
 		if r := recover(); r != nil {
@@ -55,7 +89,7 @@ func SetEventStreamHeaders(c *gin.Context) {
 }
 
 func ClearEventStreamHeadersIfNotWritten(c *gin.Context) {
-	if c == nil || c.Writer == nil || c.Writer.Written() {
+	if c == nil || c.Writer == nil || StreamBodyWritten(c) {
 		return
 	}
 	c.Set("event_stream_headers_set", false)
@@ -74,6 +108,7 @@ func ClaudeData(c *gin.Context, resp dto.ClaudeResponse) error {
 	} else {
 		c.Render(-1, common.CustomEvent{Data: fmt.Sprintf("event: %s\n", resp.Type)})
 		c.Render(-1, common.CustomEvent{Data: "data: " + string(jsonData)})
+		MarkStreamDataWritten(c)
 	}
 	_ = FlushWriter(c)
 	return nil
@@ -82,12 +117,14 @@ func ClaudeData(c *gin.Context, resp dto.ClaudeResponse) error {
 func ClaudeChunkData(c *gin.Context, resp dto.ClaudeResponse, data string) {
 	c.Render(-1, common.CustomEvent{Data: fmt.Sprintf("event: %s\n", resp.Type)})
 	c.Render(-1, common.CustomEvent{Data: fmt.Sprintf("data: %s\n", data)})
+	MarkStreamDataWritten(c)
 	_ = FlushWriter(c)
 }
 
 func ResponseChunkData(c *gin.Context, resp dto.ResponsesStreamResponse, data string) {
 	c.Render(-1, common.CustomEvent{Data: fmt.Sprintf("event: %s\n", resp.Type)})
 	c.Render(-1, common.CustomEvent{Data: fmt.Sprintf("data: %s", data)})
+	MarkStreamDataWritten(c)
 	_ = FlushWriter(c)
 }
 
@@ -101,6 +138,7 @@ func StringData(c *gin.Context, str string) error {
 	}
 
 	c.Render(-1, common.CustomEvent{Data: "data: " + str})
+	MarkStreamDataWritten(c)
 	return FlushWriter(c)
 }
 
@@ -116,6 +154,7 @@ func PingData(c *gin.Context) error {
 	if _, err := c.Writer.Write([]byte(": PING\n\n")); err != nil {
 		return fmt.Errorf("write ping data failed: %w", err)
 	}
+	MarkStreamBodyWritten(c)
 	return FlushWriter(c)
 }
 
diff --git a/test/e2e/mock_capture_server.go b/test/e2e/mock_capture_server.go
new file mode 100644
index 0000000..eb9a087
--- /dev/null
+++ b/test/e2e/mock_capture_server.go
@@ -0,0 +1,208 @@
+// +build ignore
+
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/QuantumNous/new-api/common"
+	"github.com/QuantumNous/new-api/middleware"
+	"github.com/gin-gonic/gin"
+)
+
+func main() {
+	gin.SetMode(gin.ReleaseMode)
+	middleware.SetCaptureEnabled(1, true)
+
+	router := gin.New()
+	router.Use(gin.Recovery())
+
+	// 模拟 TokenAuth
+	router.Use(func(c *gin.Context) {
+		auth := c.GetHeader("Authorization")
+		if auth == "" || auth == "Bearer disabled" {
+			c.JSON(401, gin.H{"error": gin.H{"message": "Unauthorized"}})
+			c.Abort()
+			return
+		}
+		c.Set("id", 1)
+		c.Next()
+	})
+
+	// 模拟 RequestId
+	router.Use(func(c *gin.Context) {
+		reqID := c.GetHeader(common.RequestIdKey)
+		if reqID == "" {
+			reqID = fmt.Sprintf("req-%d", time.Now().UnixNano())
+		}
+		c.Set(common.RequestIdKey, reqID)
+		c.Next()
+	})
+
+	router.Use(middleware.RelayCaptureMiddleware())
+
+	// ═══════════════════════════════════════════════════════
+	// OpenAI Chat Completions API
+	// ═══════════════════════════════════════════════════════
+	router.POST("/v1/chat/completions", func(c *gin.Context) {
+		stream := c.Query("stream") == "true"
+		if stream {
+			c.Header("Content-Type", "text/event-stream")
+			f := c.Writer.(http.Flusher)
+			for _, s := range []string{
+				"data: {\"id\":\"chatcmpl-001\",\"choices\":[{\"delta\":{\"content\":\"Hello \"}}]}\n\n",
+				"data: {\"id\":\"chatcmpl-001\",\"choices\":[{\"delta\":{\"content\":\"World!\"}}]}\n\n",
+				"data: [DONE]\n\n",
+			} {
+				c.Writer.Write([]byte(s))
+				f.Flush()
+			}
+			return
+		}
+		c.JSON(200, gin.H{
+			"id":      "chatcmpl-001",
+			"object":  "chat.completion",
+			"model":   "gpt-4",
+			"choices": []gin.H{{"index": 0, "message": gin.H{"role": "assistant", "content": "Hello from Chat Completions!"}}},
+			"usage":   gin.H{"prompt_tokens": 5, "completion_tokens": 5, "total_tokens": 10},
+		})
+	})
+
+	// ═══════════════════════════════════════════════════════
+	// OpenAI Responses API (new)
+	// ═══════════════════════════════════════════════════════
+	router.POST("/v1/responses", func(c *gin.Context) {
+		c.JSON(200, gin.H{
+			"id":     "resp_abc123",
+			"object": "response",
+			"status": "completed",
+			"output": []gin.H{{
+				"type": "message",
+				"role": "assistant",
+				"content": []gin.H{{
+					"type": "output_text",
+					"text": "Hello from Responses API!",
+				}},
+			}},
+			"usage": gin.H{"input_tokens": 8, "output_tokens": 4, "total_tokens": 12},
+		})
+	})
+
+	// ═══════════════════════════════════════════════════════
+	// Claude Messages API (Anthropic)
+	// ═══════════════════════════════════════════════════════
+	router.POST("/v1/messages", func(c *gin.Context) {
+		c.JSON(200, gin.H{
+			"id":         "msg_01AbCdEfGhIjKlMnOpQrStUv",
+			"type":       "message",
+			"role":       "assistant",
+			"model":      "claude-sonnet-4-6",
+			"content":    []gin.H{{"type": "text", "text": "Hello! How can I assist you today?"}},
+			"stop_reason": "end_turn",
+			"usage":      gin.H{"input_tokens": 8, "output_tokens": 12},
+		})
+	})
+
+	// ═══════════════════════════════════════════════════════
+	// Gemini Native API (/v1beta/models/*)
+	// ═══════════════════════════════════════════════════════
+	router.POST("/v1beta/models/*path", func(c *gin.Context) {
+		path := c.Param("path")
+		c.JSON(200, gin.H{
+			"candidates": []gin.H{{
+				"content": gin.H{
+					"role":  "model",
+					"parts": []gin.H{{"text": fmt.Sprintf("Gemini response for: /%s", path)}},
+				},
+				"finishReason": "STOP",
+			}},
+			"usageMetadata": gin.H{"promptTokenCount": 5, "candidatesTokenCount": 10, "totalTokenCount": 15},
+		})
+	})
+
+	// ═══════════════════════════════════════════════════════
+	// Gemini via /v1/models/* (main route)
+	// ═══════════════════════════════════════════════════════
+	router.POST("/v1/models/*path", func(c *gin.Context) {
+		path := c.Param("path")
+		c.JSON(200, gin.H{
+			"candidates": []gin.H{{
+				"content": gin.H{
+					"role":  "model",
+					"parts": []gin.H{{"text": fmt.Sprintf("Gemini(v1) response for: /%s", path)}},
+				},
+				"finishReason": "STOP",
+			}},
+		})
+	})
+
+	// ═══════════════════════════════════════════════════════
+	// Models list
+	// ═══════════════════════════════════════════════════════
+	router.GET("/v1/models", func(c *gin.Context) {
+		c.JSON(200, gin.H{"data": []gin.H{{"id": "gpt-4"}, {"id": "claude-3"}, {"id": "gemini-2.0-flash"}}})
+	})
+
+	// ═══════════════════════════════════════════════════════
+	// Error endpoint for testing error status codes
+	// ═══════════════════════════════════════════════════════
+	router.POST("/v1/error", func(c *gin.Context) {
+		code := 500
+		if c := c.Query("code"); c != "" {
+			fmt.Sscanf(c, "%d", &code)
+		}
+		c.JSON(code, gin.H{"error": gin.H{"message": "test error", "type": "test_error"}})
+	})
+
+	// ═══════════════════════════════════════════════════════
+	// Capture file management endpoints
+	// ═══════════════════════════════════════════════════════
+	router.GET("/health", func(c *gin.Context) {
+		c.JSON(200, gin.H{"status": "ok"})
+	})
+
+	router.GET("/capture-files", func(c *gin.Context) {
+		today := time.Now().Format("2006-01-02")
+		dir := fmt.Sprintf("./data/relay-capture/%s", today)
+		entries, err := os.ReadDir(dir)
+		if err != nil {
+			c.JSON(200, gin.H{"files": []string{}, "error": err.Error()})
+			return
+		}
+		var files []string
+		for _, e := range entries {
+			files = append(files, e.Name())
+		}
+		c.JSON(200, gin.H{"dir": dir, "files": files})
+	})
+
+	router.GET("/capture-files/:name", func(c *gin.Context) {
+		today := time.Now().Format("2006-01-02")
+		path := fmt.Sprintf("./data/relay-capture/%s/%s", today, c.Param("name"))
+		data, err := os.ReadFile(path)
+		if err != nil {
+			c.JSON(404, gin.H{"error": err.Error()})
+			return
+		}
+		var record map[string]interface{}
+		json.Unmarshal(data, &record)
+		c.JSON(200, record)
+	})
+
+	router.DELETE("/capture-files", func(c *gin.Context) {
+		os.RemoveAll("./data/relay-capture")
+		c.JSON(200, gin.H{"status": "cleaned"})
+	})
+
+	port := "18080"
+	if p := os.Getenv("PORT"); p != "" {
+		port = p
+	}
+	log.Printf("Mock Relay Server on :%s (chat|responses|messages|gemini)", port)
+	http.ListenAndServe(":"+port, router)
+}