Model Versioning
Keeping track of which model and which prompt version are running in production, so you can test changes safely and roll back if something breaks. The mechanics changed: from the Claude 4.6 generation onward, every model ID is a pinned snapshot, including the dateless ones like `claude-opus-5`. There is no silently-updating "latest" to guard against on current models. What you do have to plan for is retirement — Claude Opus 4.1 was retired on 5 August 2026, and calls to a retired model return an error rather than falling back.
In practice
You pin `claude-opus-5` in your API calls and record which prompt version it was evaluated against. The model won't change underneath you — dateless IDs from the 4.6 generation on are their own pinned snapshots. What will happen eventually is a retirement notice, so keep the eval suite that told you the current setup works, and check the model deprecations page when you plan quarters. A retirement with no eval suite is a migration with a deadline someone else set.
Related concepts