diff --git a/.env.example b/.env.example
index a4f392e..ddb7fef 100644
--- a/.env.example
+++ b/.env.example
@@ -77,3 +77,9 @@ DS2API_ADMIN_KEY=admin
 # VERCEL_TOKEN=your-vercel-token
 # VERCEL_PROJECT_ID=prj_xxxxxxxxxxxx
 # VERCEL_TEAM_ID=team_xxxxxxxxxxxx
+
+# Optional: Vercel deployment protection bypass secret.
+# If deployment protection is enabled, DS2API will use this value as
+# x-vercel-protection-bypass for internal Node->Go calls on Vercel.
+# You can also use VERCEL_AUTOMATION_BYPASS_SECRET directly.
+# DS2API_VERCEL_PROTECTION_BYPASS=your-bypass-secret
diff --git a/DEPLOY.en.md b/DEPLOY.en.md
index 3d09833..9c23c0f 100644
--- a/DEPLOY.en.md
+++ b/DEPLOY.en.md
@@ -152,6 +152,12 @@ Vercel is validating frontend output against `public`. This repo builds WebUI in
 
 If you manually changed Output Directory in Project Settings, set it to `static` (or clear it and let repo config apply).
 
+If API responses return Vercel HTML `Authentication Required` (instead of JSON), the request is blocked by Vercel Deployment Protection:
+
+- Disable protection for that deployment/environment (recommended for public API use)
+- Or send `x-vercel-protection-bypass` in requests
+- If only internal Node->Go calls are blocked, set `VERCEL_AUTOMATION_BYPASS_SECRET` (or `DS2API_VERCEL_PROTECTION_BYPASS`)
+
 Vercel streaming note (important):
 
 - Vercel Go Runtime applies platform-level buffering, so this repo uses a hybrid path on Vercel (`Go prepare + Node stream`) to restore real-time SSE behavior.
diff --git a/DEPLOY.md b/DEPLOY.md
index e443cb5..109f7fd 100644
--- a/DEPLOY.md
+++ b/DEPLOY.md
@@ -150,6 +150,12 @@ No Output Directory named "public" found after the Build completed.
 
 若你在项目设置里手动改过 Output Directory，请同步改为 `static` 或清空让仓库配置生效。
 
+若接口返回 Vercel 的 HTML 页面 `Authentication Required`（而不是 JSON），说明被 Vercel Deployment Protection 拦截：
+
+- 关闭该部署/环境的 Protection（推荐用于公开 API）
+- 或给请求加 `x-vercel-protection-bypass`
+- 若仅是 Vercel 内部 Node->Go 调用被拦截，可设置 `VERCEL_AUTOMATION_BYPASS_SECRET`（或 `DS2API_VERCEL_PROTECTION_BYPASS`）
+
 Vercel 流式说明（重要）：
 
 - Vercel 的 Go Runtime 存在平台层响应缓冲，因此本项目在 Vercel 上采用“Go prepare + Node stream”的混合链路来恢复实时 SSE。
diff --git a/api/chat-stream.js b/api/chat-stream.js
index 4cf05da..2742d2f 100644
--- a/api/chat-stream.js
+++ b/api/chat-stream.js
@@ -205,7 +205,10 @@ function setCorsHeaders(res) {
   res.setHeader('Access-Control-Allow-Origin', '*');
   res.setHeader('Access-Control-Allow-Credentials', 'true');
   res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, DELETE');
-  res.setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization, X-API-Key, X-Ds2-Target-Account');
+  res.setHeader(
+    'Access-Control-Allow-Headers',
+    'Content-Type, Authorization, X-API-Key, X-Ds2-Target-Account, X-Vercel-Protection-Bypass',
+  );
 }
 
 function header(req, key) {
@@ -238,6 +241,10 @@ async function fetchStreamPrepare(req, rawBody) {
   const url = new URL(`${proto}://${host}${req.url || '/v1/chat/completions'}`);
   url.searchParams.set('__go', '1');
   url.searchParams.set('__stream_prepare', '1');
+  const protectionBypass = resolveProtectionBypass(req);
+  if (protectionBypass) {
+    url.searchParams.set('x-vercel-protection-bypass', protectionBypass);
+  }
 
   const upstream = await fetch(url.toString(), {
     method: 'POST',
@@ -246,6 +253,7 @@ async function fetchStreamPrepare(req, rawBody) {
       'x-api-key': asString(header(req, 'x-api-key')),
       'x-ds2-target-account': asString(header(req, 'x-ds2-target-account')),
       'x-ds2-internal-token': internalSecret(),
+      'x-vercel-protection-bypass': protectionBypass,
       'content-type': asString(header(req, 'content-type')) || 'application/json',
     },
     body: rawBody,
@@ -269,6 +277,14 @@ async function fetchStreamPrepare(req, rawBody) {
 }
 
 function relayPreparedFailure(res, prep) {
+  if (prep.status === 401 && looksLikeVercelAuthPage(prep.text)) {
+    writeOpenAIError(
+      res,
+      401,
+      'Vercel Deployment Protection blocked internal prepare request. Disable protection for this deployment or set VERCEL_AUTOMATION_BYPASS_SECRET.',
+    );
+    return;
+  }
   res.statusCode = prep.status || 500;
   res.setHeader('Content-Type', prep.contentType || 'application/json');
   if (prep.text) {
@@ -294,6 +310,22 @@ function internalSecret() {
   return asString(process.env.DS2API_VERCEL_INTERNAL_SECRET) || asString(process.env.DS2API_ADMIN_KEY) || 'admin';
 }
 
+function resolveProtectionBypass(req) {
+  const fromHeader = asString(header(req, 'x-vercel-protection-bypass'));
+  if (fromHeader) {
+    return fromHeader;
+  }
+  return asString(process.env.VERCEL_AUTOMATION_BYPASS_SECRET) || asString(process.env.DS2API_VERCEL_PROTECTION_BYPASS);
+}
+
+function looksLikeVercelAuthPage(text) {
+  const body = asString(text).toLowerCase();
+  if (!body) {
+    return false;
+  }
+  return body.includes('authentication required') && body.includes('vercel');
+}
+
 function parseChunkForContent(chunk, thinkingEnabled, currentType) {
   if (!chunk || typeof chunk !== 'object' || !Object.prototype.hasOwnProperty.call(chunk, 'v')) {
     return { parts: [], finished: false, newType: currentType };
@@ -472,6 +504,10 @@ async function proxyToGo(req, res, rawBody) {
   const host = asString(header(req, 'host'));
   const url = new URL(`${proto}://${host}${req.url || '/v1/chat/completions'}`);
   url.searchParams.set('__go', '1');
+  const protectionBypass = resolveProtectionBypass(req);
+  if (protectionBypass) {
+    url.searchParams.set('x-vercel-protection-bypass', protectionBypass);
+  }
 
   const upstream = await fetch(url.toString(), {
     method: 'POST',
@@ -479,6 +515,7 @@ async function proxyToGo(req, res, rawBody) {
       authorization: asString(header(req, 'authorization')),
       'x-api-key': asString(header(req, 'x-api-key')),
       'x-ds2-target-account': asString(header(req, 'x-ds2-target-account')),
+      'x-vercel-protection-bypass': protectionBypass,
       'content-type': asString(header(req, 'content-type')) || 'application/json',
     },
     body: rawBody,