🧪Meta Ships LLM Test Generator That Caught 74 Privacy Bugs in H1 2026

Your next code review might come with generated tests

Meta has put LLM-generated tests into production to catch bugs at the diff stage, before code lands. The system is called Catching Just-in-Time Tests, or JiTTests, and it's already catching things traditional suites miss. Why should you care? Traditional tests can't keep up with how fast code changes at Meta's scale. JiTTests runs two tandem workflows: intent-aware, which infers what a change is trying to do and targets likely failure points, and dodgy diff, which treats every change as a potential bug and generates tests that expose behavioral differences. If you're building CI pipelines, this is a concrete pattern to steal. The numbers: 589 engineers have engaged with the system so far, and 60% of its flagged findings are true positives. In the first half of 2026, it caught 74 serious privacy bugs at the diff stage. Filtering runs through five stages, including a rule-based assessor and an LLM-as-Judge ensemble that aggregates several state-of-the-art models to sort weak catches. Human review stays in the loop, so engineers rarely have to inspect every output.