# Model version pinning

**Source:** https://promtable.com/glossary/model-version-pinning

> Model version pinning is the production practice of locking your app to a specific model snapshot (e.g., `claude-sonnet-4-6-20250101`) instead of an alias (`claude-sonnet-4-6`) — protects against silent behavior changes when the provider rolls a new snapshot.

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Model version pinning is the production practice of locking your app to a specific model snapshot (e.g., `claude-sonnet-4-6-20250101`) instead of an alias (`claude-sonnet-4-6`) — protects against silent behavior changes when the provider rolls a new snapshot.

LLM providers ship model improvements continuously. If you call the alias (`gpt-4o`, `claude-sonnet-4-6`), the provider can swap the underlying weights at any time — usually fine, but sometimes breaks edge cases your prompts relied on. Pinning to a snapshot (`gpt-4o-2024-08-06`, `claude-sonnet-4-6-20250101`) gives you stable behavior at the cost of missing improvements. Production patterns: pin in prod, test on alias in staging, plan migrations on quarterly cadence. Anthropic, OpenAI, Google all offer both alias + snapshot in 2026. The right policy: pin prod, allow alias in dev, run eval suite before promoting new snapshots.

## When to use

- Production deployments.
- Eval-driven prompt iteration.

## Common mistakes

- Using alias in prod — silent regressions when the provider rolls a new snapshot.
- Forgetting to migrate pinned versions — providers eventually deprecate old snapshots.

## Related terms

- [model-deprecation](https://promtable.com/glossary/model-deprecation)
- [evals-driven-development](https://promtable.com/glossary/evals-driven-development)

*Last updated: 2026-06-01*
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Original page: https://promtable.com/glossary/model-version-pinning
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