Claude Code 2.1.257/2.1.258: Fable 5.1 default, containment-escape hardening
Anthropic
Following v2.1.252 (Aug 31), Claude Code v2.1.257 (Sep 1) made Claude Fable 5.1 the default model (1M context, $10/$50 per Mtok), added timeFormat/timeZone settings, CLAUDE_CODE_SUBAGENT_MODEL_FORCE, and an auto-mode containment rule that stops auto-approving cloud-credential fetches and egress evasion; it also fixed symlink-based plugin path escapes and a permissions.ask bypass via compound commands. v2.1.258 (Sep 1) fixed a macOS 12 launch regression from 2.1.255 and remote-session failures after re-sent permission approvals.
Why it matters
Security tightening plus a new default frontier model for the most-used CLI coding agent
Importance: 3/5
New default frontier model plus security hardening in the most-used CLI coding agent