# Regression suite (LLM)

**Source:** https://promtable.com/glossary/regression-suite

> A regression suite is the standing set of evals that runs on every prompt change, model upgrade, or pipeline modification — designed to catch quality regressions on previously-working cases.

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A regression suite is the standing set of evals that runs on every prompt change, model upgrade, or pipeline modification — designed to catch quality regressions on previously-working cases.

Regression suites are how production LLM teams in 2026 avoid the "fixed one bug, broke five" problem. Build a golden set of representative inputs covering the use cases your product depends on. On every prompt change, run the suite. Compare new scores vs baseline. Block merges on regressions past a configurable threshold. Tools: Braintrust, Langfuse, LangSmith, Inspect Evals, custom Python + pytest. The discipline is to grow the suite over time — every production bug becomes a new eval case.

## When to use

- Any production LLM feature with evolving prompts or models.
- Multi-author prompt collaboration.

## Common mistakes

- Suite too small or unrepresentative — passes won't predict production.
- No clear regression threshold — debates over every score change.

## Related terms

- [evals](https://promtable.com/glossary/evals)
- [evals-driven-development](https://promtable.com/glossary/evals-driven-development)
- [shadow-deployment](https://promtable.com/glossary/shadow-deployment)

*Last updated: 2026-06-01*
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Original page: https://promtable.com/glossary/regression-suite
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