diff --git a/changelog.d/features/6709-xai-responses-endpoint.md b/changelog.d/features/6709-xai-responses-endpoint.md
new file mode 100644
index 0000000000..d828e6a7b8
--- /dev/null
+++ b/changelog.d/features/6709-xai-responses-endpoint.md
@@ -0,0 +1 @@
+- **feat(xai):** route xAI clients to Grok's native `/v1/responses` endpoint instead of the chat-completions bridge. (thanks @ryanngit)
diff --git a/open-sse/config/providers/registry/xai/index.ts b/open-sse/config/providers/registry/xai/index.ts
index 501fa4fcbf..f33e247080 100644
--- a/open-sse/config/providers/registry/xai/index.ts
+++ b/open-sse/config/providers/registry/xai/index.ts
@@ -6,12 +6,23 @@ export const xaiProvider: RegistryEntry = {
   format: "openai",
   executor: "xai",
   baseUrl: "https://api.x.ai/v1/chat/completions",
+  // Port of decolua/9router#2439 (author: @ryanngit): xAI ships a native
+  // `/v1/responses` endpoint alongside `/v1/chat/completions`. Consumed by
+  // XaiExecutor.buildUrl (open-sse/executors/xai.ts) for models tagged
+  // targetFormat: "openai-responses" below.
+  responsesBaseUrl: "https://api.x.ai/v1/responses",
   authType: "apikey",
   authHeader: "bearer",
   models: [
     { id: "grok-4.3", name: "Grok 4.3" },
     { id: "grok-build-0.1", name: "Grok Build 0.1", contextLength: 256000 },
-    { id: "grok-4.20-multi-agent-0309", name: "Grok 4.20 Multi Agent" },
+    // Responses-only per upstream 9router#2439: xAI serves this id exclusively
+    // over its native /v1/responses endpoint.
+    {
+      id: "grok-4.20-multi-agent-0309",
+      name: "Grok 4.20 Multi Agent",
+      targetFormat: "openai-responses",
+    },
     { id: "grok-4.20-0309-reasoning", name: "Grok 4.20 Reasoning" },
     { id: "grok-4.20-0309-non-reasoning", name: "Grok 4.20" },
   ],
diff --git a/open-sse/executors/xai.ts b/open-sse/executors/xai.ts
index 9f806e2c5a..e5de5c037a 100644
--- a/open-sse/executors/xai.ts
+++ b/open-sse/executors/xai.ts
@@ -1,5 +1,6 @@
 import { BaseExecutor, type ProviderCredentials } from "./base.ts";
 import { PROVIDERS } from "../config/constants.ts";
+import { getModelTargetFormat } from "../config/providerModels.ts";
 
 type JsonRecord = Record<string, unknown>;
 
@@ -51,6 +52,24 @@ export class XaiExecutor extends BaseExecutor {
     super("xai", PROVIDERS.xai);
   }
 
+  /**
+   * Port of decolua/9router#2439 (author: @ryanngit): xAI ships a native
+   * `/v1/responses` endpoint alongside `/v1/chat/completions`. Models tagged
+   * `targetFormat: "openai-responses"` in the registry (currently
+   * grok-4.20-multi-agent-0309, per upstream) resolve to that endpoint instead
+   * of the default chat-completions bridge. The per-model registry tag is the
+   * single source of truth — it also drives chatCore's body translation — so
+   * the URL stays in lockstep with the translated body, mirroring the gh
+   * executor's targetFormat-driven routing (9router#102) and the "openai"
+   * -pro heuristic in open-sse/executors/default.ts.
+   */
+  buildUrl(model: string, _stream: boolean, _urlIndex = 0) {
+    if (getModelTargetFormat("xai", model) === "openai-responses") {
+      return this.config.responsesBaseUrl || this.config.baseUrl;
+    }
+    return this.config.baseUrl;
+  }
+
   transformRequest(
     model: string,
     body: unknown,
diff --git a/tests/unit/executor-xai.test.ts b/tests/unit/executor-xai.test.ts
index df5d096ecd..f8a6031e5e 100644
--- a/tests/unit/executor-xai.test.ts
+++ b/tests/unit/executor-xai.test.ts
@@ -92,3 +92,21 @@ test("leaves a plain, unlisted model id and body unchanged (no suffix, not allow
   assert.equal(out.reasoning_effort, undefined);
   assert.deepEqual(out.messages, body.messages);
 });
+
+// Port of decolua/9router#2439 (author: @ryanngit): xAI ships a native
+// `/v1/responses` endpoint. grok-4.20-multi-agent-0309 is tagged
+// targetFormat: "openai-responses" in the registry (upstream's own tag) — it
+// must resolve to xAI's native Responses URL, not the chat-completions
+// bridge, mirroring the gh executor's targetFormat-driven routing (9router#102)
+// and the "openai" -pro heuristic in open-sse/executors/default.ts.
+test("XaiExecutor.buildUrl routes the Responses-tagged model (grok-4.20-multi-agent-0309) to xAI's native /v1/responses endpoint", () => {
+  const executor = new XaiExecutor();
+  const url = executor.buildUrl("grok-4.20-multi-agent-0309", true);
+  assert.equal(url, "https://api.x.ai/v1/responses");
+});
+
+test("XaiExecutor.buildUrl keeps a plain chat model (grok-4.3) on /v1/chat/completions", () => {
+  const executor = new XaiExecutor();
+  const url = executor.buildUrl("grok-4.3", true);
+  assert.equal(url, "https://api.x.ai/v1/chat/completions");
+});