Vercel AI Updates: September 15, 2026

1. The AI SDK Harness Layer Can Now Authenticate Through a Coding Agent’s Own Subscription

Vercel. The HarnessAgent interface lets application code drive different coding agents without changes, and it now authenticates using credentials native to whichever harness is running. In direct mode it uses explicit provider environment credentials when present and otherwise falls back to a native subscription found on the host; auto behaves the same way when AI Gateway credentials are not configured. Credentials stay on the host with OAuth tokens refreshed as needed, and placeholder credentials are passed into sandboxes where supported. Eight adapters support it: Claude Code, Cline, Codex, Cursor, fx, GitHub Copilot, Grok Build, OpenCode, and Pi. No code or configuration changes are required. Source