# AI SDK harness auth: keep native subscriptions on the host boundary

On September 14, 2026, Vercel shipped native subscription authentication for the AI SDK harness layer. If you run coding agents through `HarnessAgent`, that change decides where credentials live and which bill pays for the run. The builders who miss it keep stuffing API keys into sandboxes. The builders who read it keep subscriptions on the host and pick an auth mode on purpose.

This post is for production teams already wiring Claude Code, Codex, Cursor, Copilot, or sibling harness adapters behind one application API.

---

*This is an excerpt. Read the full post at [otf-kit.dev/blog/ai-sdk-harness-native-auth](https://otf-kit.dev/blog/ai-sdk-harness-native-auth) — full-stack kits your AI coding agent can actually ship to production. [Browse the kits →](https://otf-kit.dev)*