Claude Platform release notes

June 9, 2026

• Claude Fable 5 is now available through the Messages API for developer traffic.
• Claude Fable 5 tokenizer accounting changed for fallback billing and cached tokens.

June 5, 2026

• Claude Opus 4.1 will retire from the API after Claude Opus 4.8 migration.

June 2, 2026

• The max_tokens request parameter now includes tool-use budget and refusal output tokens are not billed.
• Webhook events added a new Messages API response field for message batches.

May 30, 2026

Claude Managed Agents workflow controls changed for Claude Code sessions.