Anthropic Walled Garden Crackdown: Blocks Third-Party OAuth Tokens, Ends Subscription Arbitrage for OpenCode and Cursor Users

paddo.dev·high signal

On January 9, 2026, Anthropic blocked third-party harnesses from using Claude Pro/Max subscription OAuth tokens without warning or migration path, ending an arbitrage where a $200/month Max subscription provided $1,000+ API-equivalent access without rate limits. OpenCode (56K GitHub stars), Cursor-via-xAI, and any harness relying on subscription OAuth were immediately broken—OpenCode shipped ChatGPT Plus support within hours as a workaround. Standard API keys are unaffected; the block specifically targets subscription token reuse in non-Anthropic clients.