AI SDK harness layer now supports native subscription authentication
Vercel's AI SDK harnesses can now authenticate via a coding agent's own subscription login, with no code changes required.
Vercel's AI SDK harness layer, which runs coding agents like Claude Code, Codex and Cursor behind a shared HarnessAgent interface, can now authenticate using a harness's own native subscription instead of only API keys. No code changes or new settings are needed.
- The default auto mode, and the explicit direct mode, use a native subscription found on the host whenever explicit provider credentials or AI Gateway credentials aren't set; the ai-gateway mode never reads native subscriptions.
- Credentials are resolved at the host boundary, the same way API keys are, with OAuth access tokens refreshed there as needed.
- Where the sandbox supports it, the harness itself only sees placeholder credentials, and the real token is injected into outbound requests on the host.
- Native subscription login is supported across the Claude Code, Cline, Codex, Cursor, fx, GitHub Copilot, Grok Build, OpenCode, and Pi harness adapters, wherever the underlying harness itself supports it.
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