Claude Code 2.1.166 adds fallback models, and if you run cron pipelines this is the fix you've wanted

Two researchers in my set surfaced this independently, which is usually a sign it matters. Claude Code 2.1.166, first seen June 6, introduces a fallback-models setting: configure up to three models tried in order when the primary is overloaded or unavailable. It also adds glob pattern support in permission deny rules and explicit thinking-token controls, per Releasebot. This shipped in a fast June cadence, 2.1.160 through 2.1.166 all between June 4 and 6.

I've lost overnight runs to a single overloaded model. The pipeline stalls at 3 AM, nothing retries intelligently, and I wake up to a dead pipeline and no newsletter. Fallback models fix exactly that failure. Pair a frontier primary like Opus with cheaper fallbacks and your background session keeps progressing through peak load instead of dying on it. For anyone running unattended agents, and re-read story one, this is the reliability primitive that makes headless pipelines survivable now that they cost real money. You don't want a $200 credit pool draining into retries against an overloaded endpoint.

The glob deny rules are the quieter win and they pair with the new metering too. You can now write a * deny rule that blocks all tools as a default-deny baseline, then selectively allow back only what a task needs (skill-finder via Releasebot). Least-privilege agent configs just got a real syntax. Given this week's supply-chain news (the Miasma worm hitting Microsoft's own GitHub orgs, more below), a default-deny posture isn't paranoid anymore, it's table stakes.

There's more in the changelog worth wiring up. A new MessageDisplay hook event lets hooks transform or hide assistant message text as it renders. Stop and SubagentStop hooks can return additionalContext to feed Claude guidance and keep the turn going without tripping a hook error. SessionStart hooks can return reloadSkills: true, and a new /reload-skills command re-scans skill directories mid-session. Plugins in .claude/skills auto-load with no marketplace (Claude Code Docs). If you're building self-modifying agent setups, that's a tighter authoring loop than we had a month ago.

What to do: add a fallback-models block to every autonomous config today. Three models, frontier primary, cheaper fallbacks. Then add a * deny baseline and allow back your actual tool surface. Twenty minutes of config, and your next overnight run survives a Tuesday outage.