diff --git a/.env.example b/.env.example
index 6812b39..a4f392e 100644
--- a/.env.example
+++ b/.env.example
@@ -66,6 +66,11 @@ DS2API_ADMIN_KEY=admin
 # Default: enabled on local/Docker, disabled on Vercel.
 # DS2API_AUTO_BUILD_WEBUI=true
 
+# Internal auth secret used by the Vercel hybrid streaming path
+# (Go prepare endpoint <-> Node stream function).
+# Optional: falls back to DS2API_ADMIN_KEY when unset.
+# DS2API_VERCEL_INTERNAL_SECRET=change-me
+
 # ---------------------------------------------------------------
 # Vercel sync integration (optional)
 # ---------------------------------------------------------------
diff --git a/DEPLOY.en.md b/DEPLOY.en.md
index 42f3b48..3d09833 100644
--- a/DEPLOY.en.md
+++ b/DEPLOY.en.md
@@ -67,6 +67,9 @@ Notes:
 - Rewrites and cache headers: `vercel.json`
 - Build stage runs `npm ci --prefix webui && npm run build --prefix webui` automatically
 - `vercel.json` routes `/admin/assets/*` and the `/admin` page to static output, while `/admin/*` APIs still go to `api/index`
+- To mitigate Go Runtime streaming buffering, `/v1/chat/completions` on Vercel is routed to `api/chat-stream.js` (Node Runtime)
+- `api/chat-stream.js` automatically falls back to the Go entry for non-stream requests or requests with `tools` (internal `__go=1`)
+- `api/chat-stream.js` is data-path only (stream relay + SSE conversion); auth/account/session/PoW preparation still comes from an internal Go prepare endpoint (enabled on Vercel only)
 
 Minimum environment variables:
 
@@ -82,6 +85,7 @@ Optional:
 - `DS2API_ACCOUNT_CONCURRENCY` (alias of the same setting)
 - `DS2API_ACCOUNT_MAX_QUEUE` (waiting queue limit, default=`recommended_concurrency`)
 - `DS2API_ACCOUNT_QUEUE_SIZE` (alias of the same setting)
+- `DS2API_VERCEL_INTERNAL_SECRET` (optional internal auth secret for Vercel hybrid streaming path; falls back to `DS2API_ADMIN_KEY` when unset)
 
 Recommended concurrency is computed dynamically as `account_count * per_account_inflight_limit` (default is `account_count * 2`).
 When inflight slots are full, requests are queued first; with default queue size, 429 typically starts around `account_count * 4`.
@@ -139,14 +143,19 @@ If you see:
 No Output Directory named "public" found after the Build completed.
 ```
 
-Vercel is validating frontend output against `public`, while this repo emits WebUI assets to `static/admin`.
+Vercel is validating frontend output against `public`. This repo builds WebUI into `static/admin`, and uses the parent directory `static` as Vercel output root.
 `vercel.json` now explicitly sets:
 
 ```json
-"outputDirectory": "static/admin"
+"outputDirectory": "static"
 ```
 
-If you manually changed Output Directory in Project Settings, set it to `static/admin` (or clear it and let repo config apply).
+If you manually changed Output Directory in Project Settings, set it to `static` (or clear it and let repo config apply).
+
+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.
+- This adaptation is Vercel-only; local and Docker remain pure Go.
 
 ## 4. Reverse Proxy (Nginx)
 
diff --git a/DEPLOY.md b/DEPLOY.md
index 78f92ea..e443cb5 100644
--- a/DEPLOY.md
+++ b/DEPLOY.md
@@ -67,6 +67,9 @@ docker-compose up -d --build
 - 路由与缓存头：`vercel.json`
 - 构建阶段会自动执行 `npm ci --prefix webui && npm run build --prefix webui`
 - `vercel.json` 已将 `/admin/assets/*` 与 `/admin` 页面走静态产物，`/admin/*` API 仍走 `api/index`
+- 为缓解 Go Runtime 的流式缓冲，`/v1/chat/completions` 在 Vercel 上会优先走 `api/chat-stream.js`（Node Runtime）
+- `api/chat-stream.js` 对非流式请求或 `tools` 请求会自动回退到 Go 入口（内部 `__go=1`）
+- `api/chat-stream.js` 仅负责流式数据转发与 SSE 转换；鉴权、账号选择、会话创建、PoW 计算仍由 Go 内部 prepare 接口完成（仅 Vercel 启用）
 
 至少配置环境变量：
 
@@ -82,6 +85,7 @@ docker-compose up -d --build
 - `DS2API_ACCOUNT_CONCURRENCY`（同上别名）
 - `DS2API_ACCOUNT_MAX_QUEUE`（等待队列上限，默认=`recommended_concurrency`）
 - `DS2API_ACCOUNT_QUEUE_SIZE`（同上别名）
+- `DS2API_VERCEL_INTERNAL_SECRET`（可选，Vercel 混合流式链路内部鉴权；未设置时回退使用 `DS2API_ADMIN_KEY`）
 
 并发建议值会动态按 `账号数量 × 每账号并发上限` 计算（默认即 `账号数量 × 2`）。
 当 in-flight 满时，请求先进入等待队列；默认队列上限等于建议并发值，因此默认 429 阈值约为 `账号数量 × 4`。
@@ -138,13 +142,18 @@ Error: Command failed: go build -ldflags -s -w -o .../bootstrap .../main__vc__go
 No Output Directory named "public" found after the Build completed.
 ```
 
-说明 Vercel 正在按 `public` 校验前端产物目录。当前仓库前端产物目录是 `static/admin`，已在 `vercel.json` 显式配置：
+说明 Vercel 正在按 `public` 校验前端产物目录。当前仓库会将 WebUI 构建到 `static/admin`，并在 `vercel.json` 使用上级目录 `static` 作为输出根目录：
 
 ```json
-"outputDirectory": "static/admin"
+"outputDirectory": "static"
 ```
 
-若你在项目设置里手动改过 Output Directory，请同步改为 `static/admin` 或清空让仓库配置生效。
+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。
+
+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。
+- 该适配只在 Vercel 生效；本地与 Docker 仍走纯 Go 链路。
 
 ## 4. 反向代理（Nginx）
 
diff --git a/README.MD b/README.MD
index 7d3190b..1b5fa2c 100644
--- a/README.MD
+++ b/README.MD
@@ -87,6 +87,8 @@ docker-compose logs -f
 - 入口：`api/index.go`
 - 路由重写：`vercel.json`
 - `vercel.json` 会在构建阶段自动执行 `npm ci --prefix webui && npm run build --prefix webui`
+- `/v1/chat/completions` 在 Vercel 上默认走 `api/chat-stream.js`（Node Runtime）以保证实时 SSE
+- `api/chat-stream.js` 仅负责流式数据转发；鉴权、账号选择、会话/PoW 准备仍由 Go 内部 prepare 接口处理
 - 至少配置：
 - `DS2API_ADMIN_KEY`
 - `DS2API_CONFIG_JSON`（JSON 字符串或 Base64）
@@ -166,6 +168,7 @@ cp config.example.json config.json
 | `DS2API_WASM_PATH` | PoW wasm 文件路径 |
 | `DS2API_STATIC_ADMIN_DIR` | 管理台静态文件目录 |
 | `DS2API_AUTO_BUILD_WEBUI` | 启动时缺失 WebUI 时是否自动执行 npm build（默认：本地开启，Vercel 关闭） |
+| `DS2API_VERCEL_INTERNAL_SECRET` | Vercel 混合流式链路内部鉴权密钥（可选；未设置时回退用 `DS2API_ADMIN_KEY`） |
 | `VERCEL_TOKEN` | Vercel 同步 token（可选） |
 | `VERCEL_PROJECT_ID` | Vercel 项目 ID（可选） |
 | `VERCEL_TEAM_ID` | Vercel 团队 ID（可选） |
diff --git a/README.en.md b/README.en.md
index 143b978..31ac889 100644
--- a/README.en.md
+++ b/README.en.md
@@ -87,6 +87,8 @@ docker-compose logs -f
 - Entrypoint: `api/index.go`
 - Rewrites: `vercel.json`
 - `vercel.json` runs `npm ci --prefix webui && npm run build --prefix webui` during build
+- `/v1/chat/completions` is routed to `api/chat-stream.js` (Node Runtime) on Vercel to preserve real-time SSE
+- `api/chat-stream.js` is data-path only; auth/account/session/PoW preparation still comes from an internal Go prepare endpoint
 - Minimum env vars:
 - `DS2API_ADMIN_KEY`
 - `DS2API_CONFIG_JSON` (raw JSON or Base64)
@@ -166,6 +168,7 @@ cp config.example.json config.json
 | `DS2API_WASM_PATH` | PoW wasm path |
 | `DS2API_STATIC_ADMIN_DIR` | Admin static assets dir |
 | `DS2API_AUTO_BUILD_WEBUI` | Auto run npm build on startup when WebUI assets are missing (default: enabled locally, disabled on Vercel) |
+| `DS2API_VERCEL_INTERNAL_SECRET` | Internal auth secret for Vercel hybrid streaming path (optional; falls back to `DS2API_ADMIN_KEY` if unset) |
 | `VERCEL_TOKEN` | Vercel sync token (optional) |
 | `VERCEL_PROJECT_ID` | Vercel project ID (optional) |
 | `VERCEL_TEAM_ID` | Vercel team ID (optional) |
diff --git a/api/chat-stream.js b/api/chat-stream.js
new file mode 100644
index 0000000..4cf05da
--- /dev/null
+++ b/api/chat-stream.js
@@ -0,0 +1,543 @@
+'use strict';
+
+const DEEPSEEK_COMPLETION_URL = 'https://chat.deepseek.com/api/v0/chat/completion';
+
+const BASE_HEADERS = {
+  Host: 'chat.deepseek.com',
+  'User-Agent': 'DeepSeek/1.6.11 Android/35',
+  Accept: 'application/json',
+  'Content-Type': 'application/json',
+  'x-client-platform': 'android',
+  'x-client-version': '1.6.11',
+  'x-client-locale': 'zh_CN',
+  'accept-charset': 'UTF-8',
+};
+
+const SKIP_PATTERNS = [
+  'quasi_status',
+  'elapsed_secs',
+  'token_usage',
+  'pending_fragment',
+  'conversation_mode',
+  'fragments/-1/status',
+  'fragments/-2/status',
+  'fragments/-3/status',
+];
+
+module.exports = async function handler(req, res) {
+  setCorsHeaders(res);
+  if (req.method === 'OPTIONS') {
+    res.statusCode = 204;
+    res.end();
+    return;
+  }
+  if (req.method !== 'POST') {
+    writeOpenAIError(res, 405, 'method not allowed');
+    return;
+  }
+
+  const rawBody = await readRawBody(req);
+  let payload;
+  try {
+    payload = JSON.parse(rawBody.toString('utf8') || '{}');
+  } catch (_err) {
+    writeOpenAIError(res, 400, 'invalid json');
+    return;
+  }
+
+  // Keep all non-stream behavior on Go side to avoid compatibility regressions.
+  if (!toBool(payload.stream) || (Array.isArray(payload.tools) && payload.tools.length > 0)) {
+    await proxyToGo(req, res, rawBody);
+    return;
+  }
+
+  const prep = await fetchStreamPrepare(req, rawBody);
+  if (!prep.ok) {
+    relayPreparedFailure(res, prep);
+    return;
+  }
+
+  const model = asString(prep.body.model) || asString(payload.model);
+  const sessionID = asString(prep.body.session_id) || `chatcmpl-${Date.now()}`;
+  const deepseekToken = asString(prep.body.deepseek_token);
+  const powHeader = asString(prep.body.pow_header);
+  const completionPayload = prep.body.payload && typeof prep.body.payload === 'object' ? prep.body.payload : null;
+  const finalPrompt = asString(prep.body.final_prompt);
+  const thinkingEnabled = toBool(prep.body.thinking_enabled);
+  const searchEnabled = toBool(prep.body.search_enabled);
+
+  if (!model || !deepseekToken || !powHeader || !completionPayload) {
+    writeOpenAIError(res, 500, 'invalid vercel prepare response');
+    return;
+  }
+
+  const completionRes = await fetch(DEEPSEEK_COMPLETION_URL, {
+    method: 'POST',
+    headers: {
+      ...BASE_HEADERS,
+      authorization: `Bearer ${deepseekToken}`,
+      'x-ds-pow-response': powHeader,
+    },
+    body: JSON.stringify(completionPayload),
+  });
+
+  if (!completionRes.ok || !completionRes.body) {
+    const detail = await safeReadText(completionRes);
+    writeOpenAIError(res, 500, detail ? `Failed to get completion: ${detail}` : 'Failed to get completion.');
+    return;
+  }
+
+  res.statusCode = 200;
+  res.setHeader('Content-Type', 'text/event-stream');
+  res.setHeader('Cache-Control', 'no-cache, no-transform');
+  res.setHeader('Connection', 'keep-alive');
+  res.setHeader('X-Accel-Buffering', 'no');
+  if (typeof res.flushHeaders === 'function') {
+    res.flushHeaders();
+  }
+
+  const created = Math.floor(Date.now() / 1000);
+  let firstChunkSent = false;
+  let currentType = thinkingEnabled ? 'thinking' : 'text';
+  let thinkingText = '';
+  let outputText = '';
+  const decoder = new TextDecoder();
+  const reader = completionRes.body.getReader();
+  let buffered = '';
+
+  const sendFrame = (obj) => {
+    res.write(`data: ${JSON.stringify(obj)}\n\n`);
+    if (typeof res.flush === 'function') {
+      res.flush();
+    }
+  };
+
+  const finish = (reason) => {
+    sendFrame({
+      id: sessionID,
+      object: 'chat.completion.chunk',
+      created,
+      model,
+      choices: [{ delta: {}, index: 0, finish_reason: reason }],
+      usage: buildUsage(finalPrompt, thinkingText, outputText),
+    });
+    res.write('data: [DONE]\n\n');
+    res.end();
+  };
+
+  try {
+    // eslint-disable-next-line no-constant-condition
+    while (true) {
+      const { value, done } = await reader.read();
+      if (done) {
+        break;
+      }
+      buffered += decoder.decode(value, { stream: true });
+      const lines = buffered.split('\n');
+      buffered = lines.pop() || '';
+
+      for (const rawLine of lines) {
+        const line = rawLine.trim();
+        if (!line.startsWith('data:')) {
+          continue;
+        }
+        const dataStr = line.slice(5).trim();
+        if (!dataStr) {
+          continue;
+        }
+        if (dataStr === '[DONE]') {
+          finish('stop');
+          return;
+        }
+        let chunk;
+        try {
+          chunk = JSON.parse(dataStr);
+        } catch (_err) {
+          continue;
+        }
+        if (chunk.error || chunk.code === 'content_filter') {
+          finish('content_filter');
+          return;
+        }
+        const parsed = parseChunkForContent(chunk, thinkingEnabled, currentType);
+        currentType = parsed.newType;
+        if (parsed.finished) {
+          finish('stop');
+          return;
+        }
+
+        for (const p of parsed.parts) {
+          if (!p.text) {
+            continue;
+          }
+          if (searchEnabled && isCitation(p.text)) {
+            continue;
+          }
+          const delta = {};
+          if (!firstChunkSent) {
+            delta.role = 'assistant';
+            firstChunkSent = true;
+          }
+          if (p.type === 'thinking') {
+            thinkingText += p.text;
+            delta.reasoning_content = p.text;
+          } else {
+            outputText += p.text;
+            delta.content = p.text;
+          }
+          sendFrame({
+            id: sessionID,
+            object: 'chat.completion.chunk',
+            created,
+            model,
+            choices: [{ delta, index: 0 }],
+          });
+        }
+      }
+    }
+    finish('stop');
+  } catch (_err) {
+    finish('stop');
+  }
+};
+
+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');
+}
+
+function header(req, key) {
+  if (!req || !req.headers) {
+    return '';
+  }
+  return asString(req.headers[key.toLowerCase()]);
+}
+
+async function readRawBody(req) {
+  if (Buffer.isBuffer(req.body)) {
+    return req.body;
+  }
+  if (typeof req.body === 'string') {
+    return Buffer.from(req.body);
+  }
+  if (req.body && typeof req.body === 'object') {
+    return Buffer.from(JSON.stringify(req.body));
+  }
+  const chunks = [];
+  for await (const chunk of req) {
+    chunks.push(Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk));
+  }
+  return Buffer.concat(chunks);
+}
+
+async function fetchStreamPrepare(req, rawBody) {
+  const proto = asString(header(req, 'x-forwarded-proto')) || 'https';
+  const host = asString(header(req, 'host'));
+  const url = new URL(`${proto}://${host}${req.url || '/v1/chat/completions'}`);
+  url.searchParams.set('__go', '1');
+  url.searchParams.set('__stream_prepare', '1');
+
+  const upstream = await fetch(url.toString(), {
+    method: 'POST',
+    headers: {
+      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-ds2-internal-token': internalSecret(),
+      'content-type': asString(header(req, 'content-type')) || 'application/json',
+    },
+    body: rawBody,
+  });
+
+  const text = await upstream.text();
+  let body = {};
+  try {
+    body = JSON.parse(text || '{}');
+  } catch (_err) {
+    body = {};
+  }
+
+  return {
+    ok: upstream.ok,
+    status: upstream.status,
+    contentType: upstream.headers.get('content-type') || 'application/json',
+    text,
+    body,
+  };
+}
+
+function relayPreparedFailure(res, prep) {
+  res.statusCode = prep.status || 500;
+  res.setHeader('Content-Type', prep.contentType || 'application/json');
+  if (prep.text) {
+    res.end(prep.text);
+    return;
+  }
+  writeOpenAIError(res, prep.status || 500, 'vercel prepare failed');
+}
+
+async function safeReadText(resp) {
+  if (!resp) {
+    return '';
+  }
+  try {
+    const text = await resp.text();
+    return text.trim();
+  } catch (_err) {
+    return '';
+  }
+}
+
+function internalSecret() {
+  return asString(process.env.DS2API_VERCEL_INTERNAL_SECRET) || asString(process.env.DS2API_ADMIN_KEY) || 'admin';
+}
+
+function parseChunkForContent(chunk, thinkingEnabled, currentType) {
+  if (!chunk || typeof chunk !== 'object' || !Object.prototype.hasOwnProperty.call(chunk, 'v')) {
+    return { parts: [], finished: false, newType: currentType };
+  }
+  const pathValue = asString(chunk.p);
+  if (shouldSkipPath(pathValue)) {
+    return { parts: [], finished: false, newType: currentType };
+  }
+  if (pathValue === 'response/status' && asString(chunk.v) === 'FINISHED') {
+    return { parts: [], finished: true, newType: currentType };
+  }
+
+  let newType = currentType;
+  const parts = [];
+
+  if (pathValue === 'response/fragments' && asString(chunk.o).toUpperCase() === 'APPEND' && Array.isArray(chunk.v)) {
+    for (const frag of chunk.v) {
+      if (!frag || typeof frag !== 'object') {
+        continue;
+      }
+      const fragType = asString(frag.type).toUpperCase();
+      const content = asString(frag.content);
+      if (!content) {
+        continue;
+      }
+      if (fragType === 'THINK' || fragType === 'THINKING') {
+        newType = 'thinking';
+        parts.push({ text: content, type: 'thinking' });
+      } else if (fragType === 'RESPONSE') {
+        newType = 'text';
+        parts.push({ text: content, type: 'text' });
+      } else {
+        parts.push({ text: content, type: 'text' });
+      }
+    }
+  }
+
+  if (pathValue === 'response' && Array.isArray(chunk.v)) {
+    for (const item of chunk.v) {
+      if (!item || typeof item !== 'object') {
+        continue;
+      }
+      if (item.p === 'fragments' && item.o === 'APPEND' && Array.isArray(item.v)) {
+        for (const frag of item.v) {
+          const fragType = asString(frag && frag.type).toUpperCase();
+          if (fragType === 'THINK' || fragType === 'THINKING') {
+            newType = 'thinking';
+          } else if (fragType === 'RESPONSE') {
+            newType = 'text';
+          }
+        }
+      }
+    }
+  }
+
+  let partType = 'text';
+  if (pathValue === 'response/thinking_content') {
+    partType = 'thinking';
+  } else if (pathValue === 'response/content') {
+    partType = 'text';
+  } else if (pathValue.includes('response/fragments') && pathValue.includes('/content')) {
+    partType = newType;
+  } else if (!pathValue && thinkingEnabled) {
+    partType = newType;
+  }
+
+  const val = chunk.v;
+  if (typeof val === 'string') {
+    if (val === 'FINISHED' && (!pathValue || pathValue === 'status')) {
+      return { parts: [], finished: true, newType };
+    }
+    if (val) {
+      parts.push({ text: val, type: partType });
+    }
+    return { parts, finished: false, newType };
+  }
+
+  if (Array.isArray(val)) {
+    for (const entry of val) {
+      if (typeof entry === 'string') {
+        if (entry) {
+          parts.push({ text: entry, type: partType });
+        }
+        continue;
+      }
+      if (!entry || typeof entry !== 'object') {
+        continue;
+      }
+      if (asString(entry.p) === 'status' && asString(entry.v) === 'FINISHED') {
+        return { parts: [], finished: true, newType };
+      }
+      const content = asString(entry.content);
+      if (!content) {
+        continue;
+      }
+      const t = asString(entry.type).toUpperCase();
+      if (t === 'THINK' || t === 'THINKING') {
+        parts.push({ text: content, type: 'thinking' });
+      } else if (t === 'RESPONSE') {
+        parts.push({ text: content, type: 'text' });
+      } else {
+        parts.push({ text: content, type: partType });
+      }
+    }
+    return { parts, finished: false, newType };
+  }
+
+  if (val && typeof val === 'object') {
+    const resp = val.response && typeof val.response === 'object' ? val.response : val;
+    if (Array.isArray(resp.fragments)) {
+      for (const frag of resp.fragments) {
+        if (!frag || typeof frag !== 'object') {
+          continue;
+        }
+        const content = asString(frag.content);
+        if (!content) {
+          continue;
+        }
+        const t = asString(frag.type).toUpperCase();
+        if (t === 'THINK' || t === 'THINKING') {
+          newType = 'thinking';
+          parts.push({ text: content, type: 'thinking' });
+        } else if (t === 'RESPONSE') {
+          newType = 'text';
+          parts.push({ text: content, type: 'text' });
+        } else {
+          parts.push({ text: content, type: partType });
+        }
+      }
+    }
+  }
+  return { parts, finished: false, newType };
+}
+
+function shouldSkipPath(pathValue) {
+  if (pathValue === 'response/search_status') {
+    return true;
+  }
+  for (const p of SKIP_PATTERNS) {
+    if (pathValue.includes(p)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+function isCitation(text) {
+  return asString(text).trim().startsWith('[citation:');
+}
+
+function buildUsage(prompt, thinking, output) {
+  const promptTokens = estimateTokens(prompt);
+  const reasoningTokens = estimateTokens(thinking);
+  const completionTokens = estimateTokens(output);
+  return {
+    prompt_tokens: promptTokens,
+    completion_tokens: reasoningTokens + completionTokens,
+    total_tokens: promptTokens + reasoningTokens + completionTokens,
+    completion_tokens_details: {
+      reasoning_tokens: reasoningTokens,
+    },
+  };
+}
+
+function estimateTokens(text) {
+  const t = asString(text);
+  if (!t) {
+    return 0;
+  }
+  const n = Math.floor(Array.from(t).length / 4);
+  return n < 1 ? 1 : n;
+}
+
+async function proxyToGo(req, res, rawBody) {
+  const proto = asString(header(req, 'x-forwarded-proto')) || 'https';
+  const host = asString(header(req, 'host'));
+  const url = new URL(`${proto}://${host}${req.url || '/v1/chat/completions'}`);
+  url.searchParams.set('__go', '1');
+
+  const upstream = await fetch(url.toString(), {
+    method: 'POST',
+    headers: {
+      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')),
+      'content-type': asString(header(req, 'content-type')) || 'application/json',
+    },
+    body: rawBody,
+  });
+
+  res.statusCode = upstream.status;
+  upstream.headers.forEach((value, key) => {
+    if (key.toLowerCase() === 'content-length') {
+      return;
+    }
+    res.setHeader(key, value);
+  });
+  const bytes = Buffer.from(await upstream.arrayBuffer());
+  res.end(bytes);
+}
+
+function writeOpenAIError(res, status, message) {
+  res.statusCode = status;
+  res.setHeader('Content-Type', 'application/json');
+  res.end(
+    JSON.stringify({
+      error: {
+        message,
+        type: openAIErrorType(status),
+      },
+    }),
+  );
+}
+
+function openAIErrorType(status) {
+  switch (status) {
+    case 400:
+      return 'invalid_request_error';
+    case 401:
+      return 'authentication_error';
+    case 403:
+      return 'permission_error';
+    case 429:
+      return 'rate_limit_error';
+    case 503:
+      return 'service_unavailable_error';
+    default:
+      return status >= 500 ? 'api_error' : 'invalid_request_error';
+  }
+}
+
+function toBool(v) {
+  return v === true;
+}
+
+function asString(v) {
+  if (typeof v === 'string') {
+    return v.trim();
+  }
+  if (Array.isArray(v)) {
+    return asString(v[0]);
+  }
+  if (v == null) {
+    return '';
+  }
+  return String(v).trim();
+}
diff --git a/internal/adapter/claude/handler.go b/internal/adapter/claude/handler.go
index 83a82ac..8abd829 100644
--- a/internal/adapter/claude/handler.go
+++ b/internal/adapter/claude/handler.go
@@ -230,19 +230,21 @@ func collectDeepSeek(resp *http.Response, thinkingEnabled bool) (string, string)
 
 func (h *Handler) writeClaudeStream(w http.ResponseWriter, r *http.Request, model string, messages []any, fullText string, detected []util.ParsedToolCall) {
 	w.Header().Set("Content-Type", "text/event-stream")
-	w.Header().Set("Cache-Control", "no-cache")
+	w.Header().Set("Cache-Control", "no-cache, no-transform")
 	w.Header().Set("Connection", "keep-alive")
-	flusher, hasFlusher := w.(http.Flusher)
-	if !hasFlusher {
-		config.Logger.Warn("[claude_stream] response writer does not support flush; falling back to buffered SSE")
+	w.Header().Set("X-Accel-Buffering", "no")
+	rc := http.NewResponseController(w)
+	canFlush := rc.Flush() == nil
+	if !canFlush {
+		config.Logger.Warn("[claude_stream] response writer does not support flush; streaming may be buffered")
 	}
 	send := func(v any) {
 		b, _ := json.Marshal(v)
 		_, _ = w.Write([]byte("data: "))
 		_, _ = w.Write(b)
 		_, _ = w.Write([]byte("\n\n"))
-		if hasFlusher {
-			flusher.Flush()
+		if canFlush {
+			_ = rc.Flush()
 		}
 	}
 	messageID := fmt.Sprintf("msg_%d", time.Now().UnixNano())
diff --git a/internal/adapter/openai/handler.go b/internal/adapter/openai/handler.go
index 23d17d5..afac493 100644
--- a/internal/adapter/openai/handler.go
+++ b/internal/adapter/openai/handler.go
@@ -3,10 +3,12 @@ package openai
 import (
 	"bufio"
 	"context"
+	"crypto/subtle"
 	"encoding/json"
 	"fmt"
 	"io"
 	"net/http"
+	"os"
 	"strings"
 	"time"
 
@@ -35,6 +37,11 @@ func (h *Handler) ListModels(w http.ResponseWriter, _ *http.Request) {
 }
 
 func (h *Handler) ChatCompletions(w http.ResponseWriter, r *http.Request) {
+	if isVercelStreamPrepareRequest(r) {
+		h.handleVercelStreamPrepare(w, r)
+		return
+	}
+
 	a, err := h.Auth.Determine(r)
 	if err != nil {
 		status := http.StatusUnauthorized
@@ -106,6 +113,98 @@ func (h *Handler) ChatCompletions(w http.ResponseWriter, r *http.Request) {
 	h.handleNonStream(w, r.Context(), resp, sessionID, model, finalPrompt, thinkingEnabled, searchEnabled, toolNames)
 }
 
+func (h *Handler) handleVercelStreamPrepare(w http.ResponseWriter, r *http.Request) {
+	if !config.IsVercel() {
+		http.NotFound(w, r)
+		return
+	}
+	internalSecret := vercelInternalSecret()
+	internalToken := strings.TrimSpace(r.Header.Get("X-Ds2-Internal-Token"))
+	if internalSecret == "" || subtle.ConstantTimeCompare([]byte(internalToken), []byte(internalSecret)) != 1 {
+		writeOpenAIError(w, http.StatusUnauthorized, "unauthorized internal request")
+		return
+	}
+
+	a, err := h.Auth.Determine(r)
+	if err != nil {
+		status := http.StatusUnauthorized
+		if err == auth.ErrNoAccount {
+			status = http.StatusTooManyRequests
+		}
+		writeOpenAIError(w, status, err.Error())
+		return
+	}
+	defer h.Auth.Release(a)
+	r = r.WithContext(auth.WithAuth(r.Context(), a))
+
+	var req map[string]any
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeOpenAIError(w, http.StatusBadRequest, "invalid json")
+		return
+	}
+	if !toBool(req["stream"]) {
+		writeOpenAIError(w, http.StatusBadRequest, "stream must be true")
+		return
+	}
+	if tools, ok := req["tools"].([]any); ok && len(tools) > 0 {
+		writeOpenAIError(w, http.StatusBadRequest, "tools are not supported by vercel stream prepare")
+		return
+	}
+
+	model, _ := req["model"].(string)
+	messagesRaw, _ := req["messages"].([]any)
+	if model == "" || len(messagesRaw) == 0 {
+		writeOpenAIError(w, http.StatusBadRequest, "Request must include 'model' and 'messages'.")
+		return
+	}
+	thinkingEnabled, searchEnabled, ok := config.GetModelConfig(model)
+	if !ok {
+		writeOpenAIError(w, http.StatusServiceUnavailable, fmt.Sprintf("Model '%s' is not available.", model))
+		return
+	}
+
+	messages := normalizeMessages(messagesRaw)
+	finalPrompt := util.MessagesPrepare(messages)
+
+	sessionID, err := h.DS.CreateSession(r.Context(), a, 3)
+	if err != nil {
+		if a.UseConfigToken {
+			writeOpenAIError(w, http.StatusUnauthorized, "Account token is invalid. Please re-login the account in admin.")
+		} else {
+			writeOpenAIError(w, http.StatusUnauthorized, "Invalid token. If this should be a DS2API key, add it to config.keys first.")
+		}
+		return
+	}
+	powHeader, err := h.DS.GetPow(r.Context(), a, 3)
+	if err != nil {
+		writeOpenAIError(w, http.StatusUnauthorized, "Failed to get PoW (invalid token or unknown error).")
+		return
+	}
+	if strings.TrimSpace(a.DeepSeekToken) == "" {
+		writeOpenAIError(w, http.StatusUnauthorized, "Invalid token. If this should be a DS2API key, add it to config.keys first.")
+		return
+	}
+
+	payload := map[string]any{
+		"chat_session_id":   sessionID,
+		"parent_message_id": nil,
+		"prompt":            finalPrompt,
+		"ref_file_ids":      []any{},
+		"thinking_enabled":  thinkingEnabled,
+		"search_enabled":    searchEnabled,
+	}
+	writeJSON(w, http.StatusOK, map[string]any{
+		"session_id":       sessionID,
+		"model":            model,
+		"final_prompt":     finalPrompt,
+		"thinking_enabled": thinkingEnabled,
+		"search_enabled":   searchEnabled,
+		"deepseek_token":   a.DeepSeekToken,
+		"pow_header":       powHeader,
+		"payload":          payload,
+	})
+}
+
 func (h *Handler) handleNonStream(w http.ResponseWriter, ctx context.Context, resp *http.Response, completionID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string) {
 	defer resp.Body.Close()
 	if resp.StatusCode != http.StatusOK {
@@ -191,11 +290,13 @@ func (h *Handler) handleStream(w http.ResponseWriter, r *http.Request, resp *htt
 		return
 	}
 	w.Header().Set("Content-Type", "text/event-stream")
-	w.Header().Set("Cache-Control", "no-cache")
+	w.Header().Set("Cache-Control", "no-cache, no-transform")
 	w.Header().Set("Connection", "keep-alive")
-	flusher, hasFlusher := w.(http.Flusher)
-	if !hasFlusher {
-		config.Logger.Warn("[stream] response writer does not support flush; falling back to buffered SSE")
+	w.Header().Set("X-Accel-Buffering", "no")
+	rc := http.NewResponseController(w)
+	canFlush := rc.Flush() == nil
+	if !canFlush {
+		config.Logger.Warn("[stream] response writer does not support flush; streaming may be buffered")
 	}
 
 	lines := make(chan []byte, 128)
@@ -232,14 +333,14 @@ func (h *Handler) handleStream(w http.ResponseWriter, r *http.Request, resp *htt
 		_, _ = w.Write([]byte("data: "))
 		_, _ = w.Write(b)
 		_, _ = w.Write([]byte("\n\n"))
-		if hasFlusher {
-			flusher.Flush()
+		if canFlush {
+			_ = rc.Flush()
 		}
 	}
 	sendDone := func() {
 		_, _ = w.Write([]byte("data: [DONE]\n\n"))
-		if hasFlusher {
-			flusher.Flush()
+		if canFlush {
+			_ = rc.Flush()
 		}
 	}
 
@@ -316,9 +417,9 @@ func (h *Handler) handleStream(w http.ResponseWriter, r *http.Request, resp *htt
 				finalize("stop")
 				return
 			}
-			if hasFlusher {
+			if canFlush {
 				_, _ = w.Write([]byte(": keep-alive\n\n"))
-				flusher.Flush()
+				_ = rc.Flush()
 			}
 		case line, ok := <-lines:
 			if !ok {
@@ -483,3 +584,20 @@ func openAIErrorType(status int) string {
 		return "invalid_request_error"
 	}
 }
+
+func isVercelStreamPrepareRequest(r *http.Request) bool {
+	if r == nil {
+		return false
+	}
+	return strings.TrimSpace(r.URL.Query().Get("__stream_prepare")) == "1"
+}
+
+func vercelInternalSecret() string {
+	if v := strings.TrimSpace(os.Getenv("DS2API_VERCEL_INTERNAL_SECRET")); v != "" {
+		return v
+	}
+	if v := strings.TrimSpace(os.Getenv("DS2API_ADMIN_KEY")); v != "" {
+		return v
+	}
+	return "admin"
+}
diff --git a/internal/adapter/openai/vercel_prepare_test.go b/internal/adapter/openai/vercel_prepare_test.go
new file mode 100644
index 0000000..01b209c
--- /dev/null
+++ b/internal/adapter/openai/vercel_prepare_test.go
@@ -0,0 +1,44 @@
+package openai
+
+import (
+	"net/http/httptest"
+	"testing"
+)
+
+func TestIsVercelStreamPrepareRequest(t *testing.T) {
+	req := httptest.NewRequest("POST", "/v1/chat/completions?__stream_prepare=1", nil)
+	if !isVercelStreamPrepareRequest(req) {
+		t.Fatalf("expected prepare request to be detected")
+	}
+
+	req2 := httptest.NewRequest("POST", "/v1/chat/completions", nil)
+	if isVercelStreamPrepareRequest(req2) {
+		t.Fatalf("expected non-prepare request")
+	}
+}
+
+func TestVercelInternalSecret(t *testing.T) {
+	t.Run("prefer explicit secret", func(t *testing.T) {
+		t.Setenv("DS2API_VERCEL_INTERNAL_SECRET", "stream-secret")
+		t.Setenv("DS2API_ADMIN_KEY", "admin-fallback")
+		if got := vercelInternalSecret(); got != "stream-secret" {
+			t.Fatalf("expected explicit secret, got %q", got)
+		}
+	})
+
+	t.Run("fallback to admin key", func(t *testing.T) {
+		t.Setenv("DS2API_VERCEL_INTERNAL_SECRET", "")
+		t.Setenv("DS2API_ADMIN_KEY", "admin-fallback")
+		if got := vercelInternalSecret(); got != "admin-fallback" {
+			t.Fatalf("expected admin key fallback, got %q", got)
+		}
+	})
+
+	t.Run("default admin when env missing", func(t *testing.T) {
+		t.Setenv("DS2API_VERCEL_INTERNAL_SECRET", "")
+		t.Setenv("DS2API_ADMIN_KEY", "")
+		if got := vercelInternalSecret(); got != "admin" {
+			t.Fatalf("expected default admin fallback, got %q", got)
+		}
+	})
+}
diff --git a/vercel.json b/vercel.json
index db2bc6a..0645290 100644
--- a/vercel.json
+++ b/vercel.json
@@ -1,8 +1,27 @@
 {
   "version": 2,
   "buildCommand": "npm ci --prefix webui && npm run build --prefix webui",
-  "outputDirectory": "static/admin",
+  "outputDirectory": "static",
+  "functions": {
+    "api/chat-stream.js": {
+      "includeFiles": "**/sha3_wasm_bg.7b9ca65ddd.wasm"
+    }
+  },
   "rewrites": [
+    {
+      "source": "/v1/chat/completions",
+      "has": [
+        {
+          "type": "query",
+          "key": "__go"
+        }
+      ],
+      "destination": "/api/index"
+    },
+    {
+      "source": "/v1/chat/completions",
+      "destination": "/api/chat-stream"
+    },
     {
       "source": "/admin/login",
       "destination": "/api/index"
@@ -44,16 +63,16 @@
       "destination": "/api/index"
     },
     {
-      "source": "/admin/assets/(.*)",
-      "destination": "/assets/$1"
+      "source": "/admin",
+      "destination": "/admin/index.html"
     },
     {
-      "source": "/admin",
-      "destination": "/index.html"
+      "source": "/admin/assets/(.*)",
+      "destination": "/admin/assets/$1"
     },
     {
       "source": "/admin/(.*)",
-      "destination": "/index.html"
+      "destination": "/admin/index.html"
     },
     {
       "source": "/(.*)",