diff --git a/docs/guide/architecture/failover-circuit.md b/docs/guide/architecture/failover-circuit.md
index ebd12aa8..5f4b1be5 100644
--- a/docs/guide/architecture/failover-circuit.md
+++ b/docs/guide/architecture/failover-circuit.md
@@ -105,12 +105,14 @@ export const DEFAULT_FAILOVER_CONFIG: FailoverConfig = {
 
 代理层把两类错误判定为可故障转移：
 
-**异常类（`isFailoverableError`，`route.ts:842-863`）**：
+**异常类（`isFailoverableError`，`route.ts:844-869`）**：
 
 - `CircuitBreakerOpenError`
-- `FirstByteTimeoutError` / `StreamIdleTimeoutError`
+- `FirstByteTimeoutError` / `StreamIdleTimeoutError` / `UpstreamNoContentStreamError`
 - 错误消息包含 `timed out` / `timeout` / `econnrefused` / `econnreset` / `socket hang up` / `network` / `fetch failed` / `circuit breaker`
 
+`UpstreamNoContentStreamError` 表示上游 SSE 流正常关闭、但没有产生任何 content-bearing chunk（典型表现是只发送 `response.created` 等 metadata 事件就 `[DONE]`）。它与 `FirstByteTimeoutError` 的关键区别在于：首字超时计时器从未触发，上游是「主动提前结束流」，因此错误文案会同时携带实际耗时与配置阈值，避免把配置值误读成实际等待时长。
+
 **HTTP 响应类（`shouldTriggerFailover`，`failover-config.ts:57-73`）**：
 
 - 状态码非 2xx 且不在 `excludeStatusCodes` 中
diff --git a/src/app/api/proxy/v1/[...path]/route.ts b/src/app/api/proxy/v1/[...path]/route.ts
index 44938145..549fd86e 100644
--- a/src/app/api/proxy/v1/[...path]/route.ts
+++ b/src/app/api/proxy/v1/[...path]/route.ts
@@ -17,6 +17,7 @@ import {
   applyCompensationHeaders,
   FirstByteTimeoutError,
   StreamIdleTimeoutError,
+  UpstreamNoContentStreamError,
   type ProxyResult,
   type HeaderDiff,
 } from "@/lib/services/proxy-client";
@@ -823,6 +824,7 @@ function getErrorType(
 ): FailoverAttempt["error_type"] {
   if (error instanceof CircuitBreakerOpenError) return "circuit_open";
   if (error instanceof FirstByteTimeoutError) return "first_byte_timeout";
+  if (error instanceof UpstreamNoContentStreamError) return "upstream_no_content_stream";
   if (error instanceof StreamIdleTimeoutError) return "stream_idle_timeout";
   if (statusCode === 429) return "http_429";
   if (statusCode && statusCode >= 400 && statusCode < 500) return "http_4xx";
@@ -843,7 +845,11 @@ function isFailoverableError(error: unknown): boolean {
   if (error instanceof CircuitBreakerOpenError) {
     return true;
   }
-  if (error instanceof FirstByteTimeoutError || error instanceof StreamIdleTimeoutError) {
+  if (
+    error instanceof FirstByteTimeoutError ||
+    error instanceof StreamIdleTimeoutError ||
+    error instanceof UpstreamNoContentStreamError
+  ) {
     return true;
   }
   if (error instanceof Error) {
diff --git a/src/components/admin/routing-decision-timeline.tsx b/src/components/admin/routing-decision-timeline.tsx
index 6e8bd1f3..59dcd392 100644
--- a/src/components/admin/routing-decision-timeline.tsx
+++ b/src/components/admin/routing-decision-timeline.tsx
@@ -591,6 +591,7 @@ function RetryTimeline({
     switch (errorType) {
       case "timeout":
       case "first_byte_timeout":
+      case "upstream_no_content_stream":
       case "stream_idle_timeout":
         return <Clock className="w-3 h-3 text-status-warning" />;
       case "http_5xx":
@@ -665,6 +666,7 @@ function RetryTimeline({
                     attempt.error_type === "http_5xx" && "text-status-error",
                     (attempt.error_type === "timeout" ||
                       attempt.error_type === "first_byte_timeout" ||
+                      attempt.error_type === "upstream_no_content_stream" ||
                       attempt.error_type === "stream_idle_timeout") &&
                       "text-status-warning",
                     attempt.error_type === "http_429" && "text-orange-500",
diff --git a/src/lib/services/proxy-client.ts b/src/lib/services/proxy-client.ts
index 2a78d01a..13599174 100644
--- a/src/lib/services/proxy-client.ts
+++ b/src/lib/services/proxy-client.ts
@@ -87,6 +87,24 @@ export class StreamIdleTimeoutError extends Error {
   }
 }
 
+/**
+ * Error raised when an upstream SSE stream closes cleanly before producing any
+ * content-bearing chunk. This is distinct from FirstByteTimeoutError: the
+ * configured first-byte timer never fired — the upstream simply finished the
+ * stream early (often after sending only metadata events).
+ */
+export class UpstreamNoContentStreamError extends Error {
+  constructor(
+    public readonly elapsedMs: number,
+    public readonly firstByteTimeoutMs: number
+  ) {
+    super(
+      `Upstream closed SSE stream after ${(elapsedMs / 1000).toFixed(2)}s without producing any content-bearing chunk (first-byte timeout config: ${Math.round(firstByteTimeoutMs / 1000)}s)`
+    );
+    this.name = "UpstreamNoContentStreamError";
+  }
+}
+
 function maskSecretValue(value: string): string {
   const trimmed = value.trim();
   if (trimmed.length <= 6) return "***";
@@ -943,6 +961,8 @@ async function waitForFirstStreamContent(options: {
     return;
   }
 
+  const startedAt = Date.now();
+
   let timeoutId: ReturnType<typeof setTimeout> | null = null;
   const timeoutPromise = new Promise<never>((_resolve, reject) => {
     timeoutId = setTimeout(() => {
@@ -953,7 +973,7 @@ async function waitForFirstStreamContent(options: {
 
   const streamDoneBeforeContentPromise = options.onStreamDone.then(() => {
     if (!options.hasFirstContent()) {
-      throw new FirstByteTimeoutError(options.timeoutMs ?? 0);
+      throw new UpstreamNoContentStreamError(Date.now() - startedAt, options.timeoutMs ?? 0);
     }
   });
 
diff --git a/src/messages/en.json b/src/messages/en.json
index 355ab8c3..6fbdb403 100644
--- a/src/messages/en.json
+++ b/src/messages/en.json
@@ -587,6 +587,10 @@
     "journeyRequestNotSent": "Did not send the request upstream; the flow ended inside the gateway",
     "retryErrorType": {
       "timeout": "timeout",
+      "first_byte_timeout": "first-byte timeout",
+      "upstream_no_content_stream": "upstream no-content stream",
+      "stream_idle_timeout": "stream idle timeout",
+      "stream_error": "stream error",
       "http_5xx": "HTTP 5xx",
       "http_4xx": "HTTP 4xx",
       "http_429": "HTTP 429",
diff --git a/src/messages/zh-CN.json b/src/messages/zh-CN.json
index 16386c34..053e652f 100644
--- a/src/messages/zh-CN.json
+++ b/src/messages/zh-CN.json
@@ -592,6 +592,10 @@
     "journeyRequestNotSent": "未发送到上游，流程在网关内结束",
     "retryErrorType": {
       "timeout": "超时",
+      "first_byte_timeout": "首字超时",
+      "upstream_no_content_stream": "上游空内容流",
+      "stream_idle_timeout": "流空闲超时",
+      "stream_error": "流异常",
       "http_5xx": "5xx 错误",
       "http_4xx": "4xx 错误",
       "http_429": "429 限流",
diff --git a/src/types/api.ts b/src/types/api.ts
index 5f7469da..fd02a953 100644
--- a/src/types/api.ts
+++ b/src/types/api.ts
@@ -470,6 +470,7 @@ export interface TestUpstreamResponse {
 export type FailoverErrorType =
   | "timeout"
   | "first_byte_timeout"
+  | "upstream_no_content_stream"
   | "stream_idle_timeout"
   | "stream_error"
   | "http_5xx"
diff --git a/tests/unit/api/proxy/route.test.ts b/tests/unit/api/proxy/route.test.ts
index 126407f9..4f1beb4d 100644
--- a/tests/unit/api/proxy/route.test.ts
+++ b/tests/unit/api/proxy/route.test.ts
@@ -121,6 +121,18 @@ vi.mock("@/lib/services/proxy-client", () => {
     }
   }
 
+  class UpstreamNoContentStreamError extends Error {
+    constructor(
+      public readonly elapsedMs: number,
+      public readonly firstByteTimeoutMs: number
+    ) {
+      super(
+        `Upstream closed SSE stream after ${(elapsedMs / 1000).toFixed(2)}s without producing any content-bearing chunk (first-byte timeout config: ${Math.round(firstByteTimeoutMs / 1000)}s)`
+      );
+      this.name = "UpstreamNoContentStreamError";
+    }
+  }
+
   return {
     forwardRequest: vi.fn(),
     prepareUpstreamForProxy: vi.fn((upstream, timeoutConfig) => ({
@@ -157,6 +169,7 @@ vi.mock("@/lib/services/proxy-client", () => {
     ),
     FirstByteTimeoutError,
     StreamIdleTimeoutError,
+    UpstreamNoContentStreamError,
   };
 });
 
diff --git a/tests/unit/services/proxy-client.test.ts b/tests/unit/services/proxy-client.test.ts
index 71a880ba..d597bdfe 100644
--- a/tests/unit/services/proxy-client.test.ts
+++ b/tests/unit/services/proxy-client.test.ts
@@ -1758,7 +1758,7 @@ describe("proxy-client", () => {
       await assertion;
     });
 
-    it("should fail first-byte validation when stream closes before content-bearing data", async () => {
+    it("should raise UpstreamNoContentStreamError when stream closes before content-bearing data", async () => {
       const sseData = 'data: {"type":"response.created"}\n\ndata: [DONE]\n\n';
       const mockResponse = new Response(sseData, {
         status: 200,
@@ -1781,8 +1781,8 @@ describe("proxy-client", () => {
           "req-123"
         )
       ).rejects.toMatchObject({
-        name: "FirstByteTimeoutError",
-        timeoutMs: 1000,
+        name: "UpstreamNoContentStreamError",
+        firstByteTimeoutMs: 1000,
       });
     });