Claude Code v2.1.257: Fable 5.1 default, security hardening
ashwin-ant · ghdev · 2026-09-02
Anthropic released Claude Code v2.1.257 with key updates:
Model
- Added Claude Fable 5.1 (claude-fable-5-1) as the new default Fable model.
- Specs: 1M context, $10/$50 per Mtok (input/output), $0.25/Mtok cache reads.
Features
- Time settings: Added timeFormat and timeZone (12h, 24h, UTC, or strftime pattern).
- Security: Added "Containment Escape" rule in auto mode to block auto-approval of cloud metadata fetches, egress evasion, and cross-tenant access.
- Added CLAUDECODESUBAGENTMODELFORCE to enforce model settings on all subagents.
- Permissions: Prompt before reading files outside working directories in auto mode; option to block (permissions.blockReadsOutsideWorkingDirectories).
Fixes
- Fixed settings in .claude/ created after startup not being picked up.
- Fixed session permission mode inheritance and keybinding issues.
- Fixed background session startup failures on macOS/Windows.
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