[FEATURE] Allow OAuth tokens for Anthropic Messages API — enable subscription-based programmatic access

Summary

Claude Code's OAuth token (sk-ant-oat01-*) is rejected by the Anthropic Messages API with: "OAuth authentication is currently not supported."

This forces developers building on Claude Code to purchase separate API credits even though they already pay for a Claude subscription ($100/month for Max). This is significant friction for adoption.

Real-World Use Case

This was discovered while building ΠΑΝ (PAN) — an open-source personal AI assistant that uses Claude Code as its brain. PAN provides:

• Voice-controlled computer automation (terminal, files, browser)
• Phone app with real-time voice (Android)
• Camera vision analysis
• Cross-device orchestration

PAN's server needs to make programmatic Claude API calls for voice query responses. The flow:

1. User speaks to PAN on phone
2. Phone sends text to PAN server
3. Server needs to call Claude API for a response
4. Response spoken back to user via TTS

Initially we used claude -p (subprocess), but the process spawn overhead adds 3-5 seconds per query — unacceptable for voice conversation. Direct API calls via Haiku respond in ~500ms.

However, the OAuth token from the user's existing Claude subscription doesn't work with the API. We had to buy a separate $10 API credit package.

Impact

Every developer building automation tools, voice assistants, or AI agents on top of Claude Code hits this wall. The subscription already authorizes AI usage — the OAuth token should work for programmatic access too.

This would benefit:

• Voice assistant builders (PAN, custom assistants)
• Automation tool developers
• MCP server builders that need to make Claude calls
• Any application that extends Claude Code's capabilities

Proposed Solution

Allow sk-ant-oat01-* OAuth tokens in the Authorization: Bearer header or x-api-key header for the Messages API, respecting the user's existing subscription rate limits.

Environment

• Claude Code 2.1.79
• Claude Max subscription
• Windows 11 + Android

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This issue was co-authored by Claude (Opus 4.6) while building PAN with the developer. The limitation was encountered during real development and independently verified.