diff --git a/src/commands/models.ts b/src/commands/models.ts
index b44e8f506..5d00c736c 100644
--- a/src/commands/models.ts
+++ b/src/commands/models.ts
@@ -34,6 +34,7 @@ import {
   resolveModel,
   type ModelTier,
 } from '../core/model-config.ts';
+import { resolveRecipe } from '../core/ai/model-resolver.ts';
 
 const TIERS: ModelTier[] = ['utility', 'reasoning', 'deep', 'subagent'];
 
@@ -186,6 +187,44 @@ function classifyError(err: unknown): { status: ProbeStatus; message: string } {
   return { status: 'unknown', message: msg };
 }
 
+const OPENAI_COMPAT_V1_HINT =
+  'If the API key is correct, the base URL may be missing the /v1 suffix. ' +
+  'OpenAI-shaped proxies (codex-proxy, Azure-OpenAI mirrors, LiteLLM fronting an OpenAI route) ' +
+  'serve /v1/chat/completions and 401 on the bare path. ' +
+  'Confirm with: `curl <base>/models` returns 200 with the same bearer, then append /v1 to the base URL.';
+
+/**
+ * Fix-hint for the openai-compatible-proxy `/v1`-suffix trap.
+ *
+ * An OpenAI-shaped proxy whose base URL omits `/v1` (codex-proxy, some
+ * Azure-OpenAI mirrors, a LiteLLM proxy fronting an OpenAI-route backend)
+ * serves `/v1/chat/completions` and returns 401 on the bare `/chat/completions`
+ * the AI SDK appends to the base. `classifyError` reads that 401 as `auth` and
+ * points the operator at the bearer token, when the real fix is the URL shape.
+ *
+ * Returns the corrective hint only when the model routes through an
+ * openai-compatible recipe (proxy tier, not native anthropic/openai/google),
+ * `baseURL` is set, and `baseURL` does not already end in `/v1` (optionally with
+ * a trailing slash). Pure: recipe resolution is synchronous and does no
+ * network/engine work; any resolution failure returns undefined.
+ *
+ * @internal exported for tests.
+ */
+export function openAiCompatV1Hint(
+  modelStr: string,
+  baseURL: string | undefined | null,
+): string | undefined {
+  if (!baseURL || !baseURL.trim()) return undefined;
+  if (/\/v1\/?$/.test(baseURL.trim())) return undefined;
+  try {
+    const { recipe } = resolveRecipe(modelStr);
+    if (recipe.tier !== 'openai-compat') return undefined;
+    return OPENAI_COMPAT_V1_HINT;
+  } catch {
+    return undefined;
+  }
+}
+
 /**
  * Validate the configured embedding model + dims combo without spending tokens.
  * Catches the bug class where a brain configured for Voyage with a missing or
@@ -523,7 +562,29 @@ async function probeModel(modelStr: string, touchpoint: 'chat' | 'expansion'): P
     }
   } catch (err) {
     const { status, message } = classifyError(err);
-    return { model: modelStr, touchpoint, status, message, elapsed_ms: Date.now() - start };
+    const result: ProbeResult = { model: modelStr, touchpoint, status, message, elapsed_ms: Date.now() - start };
+    // An openai-compatible proxy whose base URL omits `/v1` returns 401 (not
+    // 404) on the bare `/chat/completions` path, which classifyError reads as
+    // `auth`. Attach the URL-shape hint so the operator doesn't chase the
+    // bearer token. Fail open: any error resolving the base URL yields no hint
+    // and never breaks the probe.
+    if (status === 'auth') {
+      try {
+        const { loadConfig } = await import('../core/config.ts');
+        const { buildGatewayConfig } = await import('../core/ai/build-gateway-config.ts');
+        const fileCfg = loadConfig();
+        if (fileCfg) {
+          const cfg = buildGatewayConfig(fileCfg);
+          const { recipe } = resolveRecipe(modelStr);
+          const baseURL = cfg.base_urls?.[recipe.id] ?? recipe.base_url_default;
+          const hint = openAiCompatV1Hint(modelStr, baseURL);
+          if (hint) result.fix = hint;
+        }
+      } catch {
+        // fail open — no hint
+      }
+    }
+    return result;
   }
 }
 
diff --git a/test/models-doctor-v1-hint.test.ts b/test/models-doctor-v1-hint.test.ts
new file mode 100644
index 000000000..1d31be99c
--- /dev/null
+++ b/test/models-doctor-v1-hint.test.ts
@@ -0,0 +1,40 @@
+import { describe, test, expect } from 'bun:test';
+import { openAiCompatV1Hint } from '../src/commands/models.ts';
+
+/**
+ * `gbrain models doctor` — the openai-compatible-proxy `/v1`-suffix hint.
+ *
+ * `openAiCompatV1Hint` is pure: it resolves the model's recipe synchronously
+ * (no network, no engine) to decide whether the provider is an openai-compatible
+ * proxy, then inspects the passed base URL. These cases pin the four branches
+ * without any transport stub.
+ */
+describe('openAiCompatV1Hint', () => {
+  test('openai-compat proxy without /v1 suffix returns a /v1 hint', () => {
+    const hint = openAiCompatV1Hint('litellm:gpt-4o', 'http://localhost:4000');
+    expect(hint).toBeDefined();
+    expect(hint).toContain('/v1');
+  });
+
+  test('base URL already ending in /v1 returns undefined', () => {
+    expect(openAiCompatV1Hint('litellm:gpt-4o', 'http://localhost:4000/v1')).toBeUndefined();
+  });
+
+  test('base URL ending in /v1/ (trailing slash) returns undefined', () => {
+    expect(openAiCompatV1Hint('litellm:gpt-4o', 'http://localhost:4000/v1/')).toBeUndefined();
+  });
+
+  test('native anthropic provider returns undefined', () => {
+    expect(openAiCompatV1Hint('anthropic:claude-sonnet-4-6', 'https://api.anthropic.com')).toBeUndefined();
+  });
+
+  test('native openai provider returns undefined', () => {
+    expect(openAiCompatV1Hint('openai:gpt-4o', 'https://api.openai.com')).toBeUndefined();
+  });
+
+  test('missing base URL returns undefined', () => {
+    expect(openAiCompatV1Hint('litellm:gpt-4o', undefined)).toBeUndefined();
+    expect(openAiCompatV1Hint('litellm:gpt-4o', null)).toBeUndefined();
+    expect(openAiCompatV1Hint('litellm:gpt-4o', '')).toBeUndefined();
+  });
+});