diff --git a/changelog.d/fixes/15946-ninerouter-400-recovery.md b/changelog.d/fixes/15946-ninerouter-400-recovery.md
new file mode 100644
index 0000000000..c386f2f500
--- /dev/null
+++ b/changelog.d/fixes/15946-ninerouter-400-recovery.md
@@ -0,0 +1 @@
+- **fix(providers):** 9router requests now reach the reactive `reasoning_effort` 400 clamp-and-retry, so an upstream that names its accepted enum is retried once with the clamped value instead of surfacing the raw 400 (#PENDING, part of #14629)
diff --git a/open-sse/executors/ninerouter.ts b/open-sse/executors/ninerouter.ts
index 2140a0ed23..d8da356d69 100644
--- a/open-sse/executors/ninerouter.ts
+++ b/open-sse/executors/ninerouter.ts
@@ -28,6 +28,7 @@ import {
 } from "./base.ts";
 import { stripInternalBodyFields } from "../config/cliFingerprints.ts";
 import { FETCH_TIMEOUT_MS } from "../config/constants.ts";
+import { applyReasoningEffortRecovery } from "./base/reasoningEffortRecovery.ts";
 import { buildErrorBody } from "../utils/error.ts";
 import { getSupervisor } from "@/lib/services/registry";
 import { getOrCreateApiKey } from "@/lib/services/apiKey";
@@ -179,14 +180,23 @@ export class NineRouterExecutor extends BaseExecutor {
       `→ ${url} (model: ${innerModel}, shape: ${shape}, port: ${dynamicPort})`
     );
 
-    const response = await fetch(url, {
-      method: "POST",
-      headers,
-      body: JSON.stringify(transformedBody),
-      signal: combinedSignal,
+    const fetchOptions = { method: "POST", headers, signal: combinedSignal };
+    const response = await fetch(url, { ...fetchOptions, body: JSON.stringify(transformedBody) });
+
+    // #14629: this override never calls super.execute(), so wire the same
+    // reactive reasoning_effort 400 clamp-and-retry BaseExecutor applies.
+    const recovery = await applyReasoningEffortRecovery({
+      response,
+      url,
+      provider: this.provider,
+      model: input.model,
+      body: transformedBody,
+      fetchOptions,
+      fetchFn: (fetchUrl, fetchOpts) => fetch(fetchUrl, fetchOpts),
+      log: input.log,
     });
 
-    return { response, url, headers, transformedBody };
+    return { response: recovery.response, url, headers, transformedBody };
   }
 
   async healthCheck(): Promise<{ ok: boolean; latencyMs: number; error?: string }> {
diff --git a/tests/unit/issue-14629-ninerouter-400-recovery.test.ts b/tests/unit/issue-14629-ninerouter-400-recovery.test.ts
new file mode 100644
index 0000000000..2085bee988
--- /dev/null
+++ b/tests/unit/issue-14629-ninerouter-400-recovery.test.ts
@@ -0,0 +1,121 @@
+// #14629: NineRouterExecutor overrides execute() without calling super.execute(),
+// so an upstream 400 naming the accepted reasoning_effort enum surfaced raw
+// instead of reaching the clamp-and-retry that BaseExecutor (and, since #14915,
+// glm and cliproxyapi) apply. 9router forwards the OpenAI-shaped body as is.
+import { describe, it, afterEach } from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+const TEST_DATA_DIR = fs.mkdtempSync(path.join(os.tmpdir(), "omniroute-ninerouter-14629-"));
+process.env.DATA_DIR = TEST_DATA_DIR;
+process.env.NODE_ENV = "test";
+process.env.DISABLE_SQLITE_AUTO_BACKUP = "true";
+
+const core = await import("../../src/lib/db/core.ts");
+core
+  .getDbInstance()
+  .prepare(
+    `INSERT OR IGNORE INTO version_manager
+       (tool, status, port, auto_start, auto_update, provider_expose)
+     VALUES ('9router', 'stopped', 20130, 0, 1, 0)`
+  )
+  .run();
+
+const { registerSupervisor, unregisterSupervisor } =
+  await import("../../src/lib/services/registry.ts");
+const { ServiceSupervisor } = await import("../../src/lib/services/ServiceSupervisor.ts");
+const { NineRouterExecutor } = await import("../../open-sse/executors/ninerouter.ts");
+const { __test_resetLearnedReasoningEffortCaps } =
+  await import("../../open-sse/services/learnedReasoningEffortCaps.ts");
+
+function registerRunningSupervisor() {
+  const sup = new ServiceSupervisor({
+    tool: "9router",
+    port: 20130,
+    spawnArgs: () => ({
+      command: process.execPath,
+      args: ["-e", "setTimeout(() => {}, 60000)"],
+      env: process.env,
+      cwd: process.cwd(),
+    }),
+    healthUrl: () => "http://127.0.0.1:20130/api/health",
+    healthIntervalMs: 2000,
+    stopTimeoutMs: 3000,
+    logsBufferBytes: 64 * 1024,
+  });
+  // @ts-ignore — patch internal state without spawning a process
+  sup["state"] = "running";
+  registerSupervisor(sup);
+}
+
+const REJECTED = JSON.stringify({
+  error: {
+    message: 'Invalid option: expected one of "low", "medium", "high"',
+    param: "reasoning_effort",
+  },
+});
+
+const originalFetch = globalThis.fetch;
+
+afterEach(() => {
+  globalThis.fetch = originalFetch;
+  unregisterSupervisor("9router");
+  __test_resetLearnedReasoningEffortCaps();
+});
+
+function mockFetch(first: Response) {
+  const calls: Array<{ url: string; body: string }> = [];
+  globalThis.fetch = (async (url: string | URL | Request, init?: RequestInit) => {
+    calls.push({ url: String(url), body: String(init?.body ?? "") });
+    if (calls.length === 1) return first;
+    return new Response(JSON.stringify({ choices: [{ message: { content: "ok" } }] }), {
+      status: 200,
+      headers: { "Content-Type": "application/json" },
+    });
+  }) as typeof fetch;
+  return calls;
+}
+
+describe("issue #14629 — 9router reaches the reactive reasoning_effort 400 recovery", () => {
+  it("clamps reasoning_effort and retries once against the same endpoint", async () => {
+    __test_resetLearnedReasoningEffortCaps();
+    registerRunningSupervisor();
+    const calls = mockFetch(new Response(REJECTED, { status: 400 }));
+
+    const result = await new NineRouterExecutor("http://127.0.0.1:20130").execute({
+      model: "9router/cx/gpt-5-mini",
+      body: { messages: [{ role: "user", content: "hi" }], reasoning_effort: "none" },
+      stream: false,
+      credentials: {},
+    });
+
+    assert.equal(calls.length, 2);
+    assert.equal(result.response.status, 200);
+    assert.equal(calls[1].url, calls[0].url);
+    const retried = JSON.parse(calls[1].body);
+    assert.equal(retried.reasoning_effort, "low");
+    assert.equal(retried.model, "cx/gpt-5-mini");
+  });
+
+  it("does not retry a 400 that names no reasoning_effort enum", async () => {
+    __test_resetLearnedReasoningEffortCaps();
+    registerRunningSupervisor();
+    const calls = mockFetch(
+      new Response(JSON.stringify({ error: { message: "messages: field required" } }), {
+        status: 400,
+      })
+    );
+
+    const result = await new NineRouterExecutor("http://127.0.0.1:20130").execute({
+      model: "9router/cx/gpt-5-mini",
+      body: { messages: [{ role: "user", content: "hi" }] },
+      stream: false,
+      credentials: {},
+    });
+
+    assert.equal(calls.length, 1);
+    assert.equal(result.response.status, 400);
+  });
+});