Claude Code adds fallback models — set the chain before your next overload

Claude Code v2.1.166 (June 6, 2026) shipped a fallbackModel setting that lets you configure up to three backup models tried in order when the primary returns a 529 Overloaded error — and --fallback-model now applies to interactive and backgrounded (/bg) sessions, not just headless runs.

Fallback fires on overload and unexpected non-retryable errors; auth, rate-limit, request-size, and transport errors still surface immediately (retrying those on another model wouldn't help). A sensible default chain for most developers is Opus 4.8 → Sonnet 4.6 → Haiku 4.5. The same release broadens deny-rule globbing and hardens cross-session message security. If you run long agent sessions, CI pipelines, or background workers, this is a cheap reliability win against the overload windows that otherwise kill a job mid-task.

Sources: AI for Anything: fallbackModel guide, Releasebot: Claude Code June 2026, Claude Code changelog, Video walkthrough