Anthropic model update history — how to track Claude version changes

Anthropic publishes its model release timeline at docs.anthropic.com under "Models overview" and "Model deprecations." Key dated snapshots: claude-2.0 (Jul 2023), claude-2.1 (Nov 2023), claude-3-haiku-20240307, claude-3-sonnet-20240229, claude-3-opus-20240229, claude-3-5-sonnet-20240620, claude-3-5-haiku-20241022, claude-3-5-sonnet-20241022 (the "new Sonnet"), and the Claude 3.7 / Claude 4 family. The *-latest aliases re-point across these, which is the primary source of "Claude changed overnight" reports.

To track changes yourself, subscribe to Anthropic's changelog RSS, watch the deprecation page, and pin to dated snapshots in code. For behavior-level diffs (not just version strings), you need eval data on each snapshot — ModelWatch maintains historical eval scores per Claude snapshot and exposes a per-model history view at modelwatch.app/claude/<snapshot>.