Native Mac apps can authenticate against a user's existing LLM subscription (Claude Pro/Max, ChatGPT Plus/Pro, Gemini, GitHub Copilot) instead of requiring separate API keys. This is done via OAuth 2.0 with PKCE — the same protocol used for "Sign in with Google/Apple/GitHub" flows, adapted here to obtain short-lived API access tokens tied to the user's consumer subscription.
Result: Users pay nothing extra. All inference runs against their existing subscription quota.