The way I read the Anthropic docs, it seems the term plan is to block the usage of OAuth credentials with the "Claude Agent SDK".

This URL: https://code.claude.com/docs/en/agent-sdk/overview

Says this: "Unless previously approved, Anthropic does not allow third party developers to offer claude.ai login or rate limits for their products, including agents built on the Claude Agent SDK. Please use the API key authentication methods described in this document instead."

Again, it seems Anthropic prefers to bill API token rates (long run), not subscriber effective token rates.