diff --git a/open-sse/translator/formats.js b/open-sse/translator/formats.js
index c32835d..9ad2245 100644
--- a/open-sse/translator/formats.js
+++ b/open-sse/translator/formats.js
@@ -12,3 +12,20 @@ export const FORMATS = {
   CURSOR: "cursor"
 };
 
+// Map endpoint suffix → source format (takes priority over body-based detection)
+const ENDPOINT_FORMAT_MAP = {
+  "/v1/responses": FORMATS.OPENAI_RESPONSES,
+  "/v1/chat/completions": FORMATS.OPENAI,
+};
+
+/**
+ * Detect source format from request URL pathname.
+ * Returns null if no matching endpoint found.
+ */
+export function detectFormatByEndpoint(pathname) {
+  for (const [segment, format] of Object.entries(ENDPOINT_FORMAT_MAP)) {
+    if (pathname.includes(segment)) return format;
+  }
+  return null;
+}
+
diff --git a/open-sse/translator/request/openai-responses.js b/open-sse/translator/request/openai-responses.js
index 66e0541..a47d27f 100644
--- a/open-sse/translator/request/openai-responses.js
+++ b/open-sse/translator/request/openai-responses.js
@@ -143,6 +143,9 @@ export function openaiResponsesToOpenAIRequest(model, body, stream, credentials)
  * Convert OpenAI Chat Completions to OpenAI Responses API format
  */
 export function openaiToOpenAIResponsesRequest(model, body, stream, credentials) {
+  // Body already in Responses API format (e.g. Cursor CLI calling /chat/completions with input[])
+  if (body.input) return { ...body, model, stream: true };
+
   const result = {
     model,
     input: [],
diff --git a/package.json b/package.json
index 11b684e..729e02a 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "9router-app",
-  "version": "0.3.18",
+  "version": "0.3.19",
   "description": "9Router web dashboard",
   "private": true,
   "scripts": {
diff --git a/src/sse/handlers/chat.js b/src/sse/handlers/chat.js
index 5a1bd03..9c65ea7 100644
--- a/src/sse/handlers/chat.js
+++ b/src/sse/handlers/chat.js
@@ -13,6 +13,7 @@ import { handleChatCore } from "open-sse/handlers/chatCore.js";
 import { errorResponse, unavailableResponse } from "open-sse/utils/error.js";
 import { handleComboChat } from "open-sse/services/combo.js";
 import { HTTP_STATUS } from "open-sse/config/constants.js";
+import { detectFormatByEndpoint } from "open-sse/translator/formats.js";
 import * as log from "../utils/logger.js";
 import { updateProviderCredentials, checkAndRefreshToken } from "../services/tokenRefresh.js";
 import { getProjectIdForConnection } from "open-sse/services/projectId.js";
@@ -180,6 +181,8 @@ async function handleSingleModelChat(body, modelStr, clientRawRequest = null, re
       connectionId: credentials.connectionId,
       userAgent,
       apiKey,
+      // Detect source format by endpoint — /chat/completions is always openai, /responses is always openai-responses
+      sourceFormatOverride: request?.url ? detectFormatByEndpoint(new URL(request.url).pathname) : null,
       onCredentialsRefreshed: async (newCreds) => {
         await updateProviderCredentials(credentials.connectionId, {
           accessToken: newCreds.accessToken,