diff --git a/src/mcplocal/src/providers/anthropic.ts b/src/mcplocal/src/providers/anthropic.ts
index 84f5db9..7cadc83 100644
--- a/src/mcplocal/src/providers/anthropic.ts
+++ b/src/mcplocal/src/providers/anthropic.ts
@@ -101,6 +101,15 @@ export class AnthropicProvider implements LlmProvider {
         res.on('data', (chunk: Buffer) => chunks.push(chunk));
         res.on('end', () => {
           const raw = Buffer.concat(chunks).toString('utf-8');
+          // Surface transport failures (e.g. a 404 "model not found" or a 401
+          // for an OAuth-gated key) instead of parsing the error body as a
+          // completion — otherwise it slips through as an empty completion and
+          // the gate reports the misleading "did not contain valid JSON".
+          const status = res.statusCode ?? 0;
+          if (status >= 400) {
+            reject(new Error(`Anthropic HTTP ${status}: ${raw.slice(0, 300)}`));
+            return;
+          }
           try {
             resolve(JSON.parse(raw));
           } catch {
diff --git a/src/mcplocal/tests/anthropic-provider.test.ts b/src/mcplocal/tests/anthropic-provider.test.ts
new file mode 100644
index 0000000..8afd7f5
--- /dev/null
+++ b/src/mcplocal/tests/anthropic-provider.test.ts
@@ -0,0 +1,51 @@
+/**
+ * AnthropicProvider — transport-error surfacing (parity with OpenAiProvider).
+ *
+ * A 404 "model not found" (OAuth-gated key on an unavailable model) or a 401
+ * must reject with the status + body, not parse the error body as an empty
+ * completion (which the gate then misreports as "did not contain valid JSON").
+ */
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+
+let mockStatus = 200;
+let mockBody = JSON.stringify({ content: [{ type: 'text', text: 'ok' }], usage: {}, stop_reason: 'end_turn' });
+
+vi.mock('node:https', () => {
+  const request = vi.fn((_opts: unknown, cb?: unknown) => {
+    const res = {
+      statusCode: mockStatus,
+      on: (event: string, handler: (d?: unknown) => void) => {
+        if (event === 'data') handler(Buffer.from(mockBody));
+        if (event === 'end') handler();
+        return res;
+      },
+    };
+    if (typeof cb === 'function') (cb as (r: unknown) => void)(res);
+    return { on: vi.fn().mockReturnThis(), write: vi.fn(), end: vi.fn() };
+  });
+  return { default: { request }, request };
+});
+
+const { AnthropicProvider } = await import('../src/providers/anthropic.js');
+
+describe('AnthropicProvider transport handling', () => {
+  beforeEach(() => {
+    mockStatus = 200;
+    mockBody = JSON.stringify({ content: [{ type: 'text', text: 'ok' }], usage: {}, stop_reason: 'end_turn' });
+  });
+
+  it('rejects on HTTP 404 (model not found) instead of masking it as bad JSON', async () => {
+    mockStatus = 404;
+    mockBody = JSON.stringify({ type: 'error', error: { type: 'not_found_error', message: 'model: claude-opus-4' } });
+    const p = new AnthropicProvider({ apiKey: 'sk-ant-oat01-x' });
+    await expect(
+      p.complete({ messages: [{ role: 'user', content: 'hi' }], maxTokens: 8 }),
+    ).rejects.toThrow(/Anthropic HTTP 404/);
+  });
+
+  it('still returns the completion on 200', async () => {
+    const p = new AnthropicProvider({ apiKey: 'sk-ant-oat01-x' });
+    const r = await p.complete({ messages: [{ role: 'user', content: 'hi' }], maxTokens: 8 });
+    expect(r.content).toBe('ok');
+  });
+});