diff --git a/README.md b/README.md
index a335422..aa68896 100644
--- a/README.md
+++ b/README.md
@@ -140,6 +140,7 @@ curl http://localhost:8080/v1/chat/completions \
 - 自动完成 Chat Completions / Anthropic / Gemini ↔ Codex Responses API 双向协议转换
 - **Structured Outputs** — `response_format`（`json_object` / `json_schema`）和 Gemini `responseMimeType`
 - **Function Calling** — 原生 `function_call` / `tool_calls` 支持（所有协议）
+- 若使用自定义 API Keys，则仅兼容 OpenAI（`/v1/chat/completions`）格式。
 
 ### 🔐 账号管理与智能轮换
 - **OAuth PKCE 登录** — 浏览器一键授权，无需手动复制 Token
diff --git a/README_EN.md b/README_EN.md
index cdba9a8..8506f89 100644
--- a/README_EN.md
+++ b/README_EN.md
@@ -115,6 +115,7 @@ If you see streaming AI text, the setup is working. If you get 401, double-check
 - Automatic bidirectional translation between all protocols and Codex Responses API
 - **Structured Outputs** — `response_format` (`json_object` / `json_schema`) and Gemini `responseMimeType`
 - **Function Calling** — native `function_call` / `tool_calls` across all protocols
+- If using custom API Keys, only the OpenAI (`/v1/chat/completions`) format is supported.
 
 ### 2. 🔐 Account Management & Smart Rotation
 - **OAuth PKCE login** — one-click browser auth