From bafaa516a912a51bca7972f09bd94f81067fbb4c Mon Sep 17 00:00:00 2001
From: Ted Slusser <ted.slusser@gmail.com>
Date: Tue, 16 Jun 2026 18:24:23 -0700
Subject: [PATCH] fix(models): normalize bare-host ANTHROPIC_BASE_URL in
 getAnthropicProvider

AI coding harnesses (Claude Code, Cursor) export ANTHROPIC_BASE_URL as a
bare host (https://api.anthropic.com, no /v1) for their own runtime.
@ai-sdk/anthropic prefers this env var over its https://api.anthropic.com/v1
default and uses it verbatim, so getAnthropicProvider()'s createAnthropic({
apiKey }) call (no baseURL) silently inherits the bare host and every
Anthropic request 404s at .../messages. Other providers (e.g. Gemini) keep
working, so consensus runs look half-broken with nothing pointing at the env.

Normalize the env value (append /v1 when it lacks a version path) and pass it
explicitly as baseURL. Unset env returns undefined so the provider keeps its
own default. Scoped to the direct path; the gateway path already sets baseURL.

Closes #57. See vercel/ai#15542 for the upstream SDK issue.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 src/__tests__/models.test.ts | 47 ++++++++++++++++++++++++++++++++++++
 src/models.ts                | 23 ++++++++++++++++++
 2 files changed, 70 insertions(+)
 create mode 100644 src/__tests__/models.test.ts

diff --git a/src/__tests__/models.test.ts b/src/__tests__/models.test.ts
new file mode 100644
index 0000000..27be216
--- /dev/null
+++ b/src/__tests__/models.test.ts
@@ -0,0 +1,47 @@
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { normalizedAnthropicBaseURL } from "../models";
+
+describe("normalizedAnthropicBaseURL", () => {
+  const original = process.env.ANTHROPIC_BASE_URL;
+
+  beforeEach(() => {
+    delete process.env.ANTHROPIC_BASE_URL;
+  });
+
+  afterEach(() => {
+    if (original === undefined) {
+      delete process.env.ANTHROPIC_BASE_URL;
+    } else {
+      process.env.ANTHROPIC_BASE_URL = original;
+    }
+  });
+
+  it("returns undefined when ANTHROPIC_BASE_URL is unset", () => {
+    expect(normalizedAnthropicBaseURL()).toBeUndefined();
+  });
+
+  it("appends /v1 to a bare host (Claude Code / Cursor style)", () => {
+    process.env.ANTHROPIC_BASE_URL = "https://api.anthropic.com";
+    expect(normalizedAnthropicBaseURL()).toBe("https://api.anthropic.com/v1");
+  });
+
+  it("trims a trailing slash before appending /v1", () => {
+    process.env.ANTHROPIC_BASE_URL = "https://api.anthropic.com/";
+    expect(normalizedAnthropicBaseURL()).toBe("https://api.anthropic.com/v1");
+  });
+
+  it("leaves a value that already ends in /v1 unchanged", () => {
+    process.env.ANTHROPIC_BASE_URL = "https://api.anthropic.com/v1";
+    expect(normalizedAnthropicBaseURL()).toBe("https://api.anthropic.com/v1");
+  });
+
+  it("leaves a value that ends in /v1/ unchanged", () => {
+    process.env.ANTHROPIC_BASE_URL = "https://api.anthropic.com/v1/";
+    expect(normalizedAnthropicBaseURL()).toBe("https://api.anthropic.com/v1/");
+  });
+
+  it("normalizes a custom proxy host", () => {
+    process.env.ANTHROPIC_BASE_URL = "https://proxy.internal/anthropic";
+    expect(normalizedAnthropicBaseURL()).toBe("https://proxy.internal/anthropic/v1");
+  });
+});
diff --git a/src/models.ts b/src/models.ts
index 47d6b88..27a48bb 100644
--- a/src/models.ts
+++ b/src/models.ts
@@ -34,6 +34,28 @@ function getGoogleProvider() {
   return _google;
 }
 
+/**
+ * Normalize a bare-host `ANTHROPIC_BASE_URL`.
+ *
+ * AI coding harnesses (Claude Code, Cursor) export `ANTHROPIC_BASE_URL` without
+ * the `/v1` suffix for their own runtime. `@ai-sdk/anthropic` prefers this env
+ * var over its `https://api.anthropic.com/v1` default and uses it verbatim, so
+ * a bare host drops `/v1` and every request 404s at `.../messages` — while
+ * other providers (e.g. Gemini) keep working, making consensus runs look
+ * half-broken. Append `/v1` when the configured base lacks a version path.
+ *
+ * Returns `undefined` when the env var is unset so the provider falls back to
+ * its own default. Remove once the SDK normalizes upstream.
+ *
+ * @see https://github.com/bug0inc/passmark/issues/57
+ * @see https://github.com/vercel/ai/issues/15542
+ */
+export function normalizedAnthropicBaseURL(): string | undefined {
+  const base = process.env.ANTHROPIC_BASE_URL;
+  if (!base) return undefined;
+  return /\/v1\/?$/.test(base) ? base : `${base.replace(/\/$/, "")}/v1`;
+}
+
 function getAnthropicProvider() {
   if (!_anthropic) {
     if (!process.env.ANTHROPIC_API_KEY) {
@@ -43,6 +65,7 @@ function getAnthropicProvider() {
     }
     _anthropic = createAnthropic({
       apiKey: process.env.ANTHROPIC_API_KEY,
+      baseURL: normalizedAnthropicBaseURL(),
     });
   }
   return _anthropic;