Claude Code 2.1.311: ultrathink now hits xhigh via the API

Anthropic shipped Claude Code 2.1.311 and 2.1.312 on October 26–27, 2026. The ultrathink keyword now runs turns at xhigh effort on Opus 5.5, Sonnet 5.5, Haiku 5.5 and Fable 5.1 through the API, and the usage window is renamed from "session limit" to "5-hour limit". The releases carry 56 and 22 bug fixes.

• ultrathink in the terminal triggers xhigh on four models via the API
• Session limit renamed to "5-hour limit", VS Code shows reset time
• 2.1.311 has 56 fixes, 2.1.312 adds 22 more
• Hooks capped at 24 concurrent runs per session