Claude Code v2.1.251 repo
Claude Code CLI release v2.1.251, shipped 2026-08-28, introducing PreModelSwitch and PostModelSwitch hook events, enriched SessionStart resume hooks with session staleness score and estimated re-cache cost, live streaming of foreground subagent tool calls and results to Remote Control clients, a Spend limit bar in /usage, and a per-session prompt-cache efficiency line in /cost.
What it does for you: The new PreModelSwitch and PostModelSwitch hook events let Axion intercept model changes mid-run and block, confirm, or annotate them, closing the gap where a scheduled task could silently escalate to a more expensive model. The enriched SessionStart resume hooks now expose how stale a session is and what a cache miss will cost, so YY's SessionStart hook can skip or warn before an expensive restart. Foreground subagent streaming makes multi-agent Axion pipelines observable in real time through Remote Control clients.
In practice: The richest Claude Code release since the hooks system launched: two entirely new hook event types and substantive observability improvements shipped in a single patch.
For: Claude (Axion). Claude Code CLI; hook events and session features run inside Claude Code sessions only.
Verdict: build now. PreModelSwitch and PostModelSwitch hook events are new capability that Axion can implement immediately. SessionStart staleness context directly addresses the scheduled-task resume gap. Score 33 clears the build-now threshold of 32 used this issue.
Build #1 Claude Code v2.1.251: use the ai-implementation-build-intake skill to build this safely. Source: https://github.com/anthropics/claude-code/releases/tag/v2.1.251. Save canonical skill/agent under AXION\Skills and AXION\Agents.
Source · Release notes published 2026-08-28 on GitHub under tag v2.1.251. 4 distinct new features listed. 2 new hook event types (PreModelSwitch, PostModelSwitch). Rapid patch cadence: 6 releases from v2.1.246 to v2.1.251 in 7 days.