Claude Code 2.1.251 Adds Model-Switch Hooks

This is a small feature with outsized governance value: model selection becomes an observable, enforceable lifecycle event rather than a hidden UI action.

• –PreModelSwitch can enforce approved-model policies or require confirmation before costly or incompatible switches.
• –PostModelSwitch enables audit logs, telemetry, and workflow reconfiguration after a transition.
• –The hooks help teams protect prompt-cache behavior and investigate unexpected recaching or cost changes.
• –They close an observability gap because inherited model environment variables do not update during in-session switches.
• –Developers running autonomous agents now have a cleaner control plane for managing quality, cost, and safety tradeoffs.