Replit uses Antithesis simulation testing to check AI-written code
Replit CTO Louis Chavez said AI models work probabilistically, making it hard to catch every software problem without controlled test runs.
Replit uses the deterministic simulation testing platform built by Virginia-based software verification startup Antithesis to check software produced with AI, the company's CTO Louis Chavez said, as reported by The Information on October 15.
Antithesis's commercial platform runs software inside a controlled virtual environment and injects faults such as network latency and server or storage failures. Its own hypervisor governs execution order, timing and network conditions so that a failing run can be reproduced exactly.
Chavez said AI models work probabilistically, so results differ between runs and it is very hard to find all software problems that way.
Antithesis CEO Will Wilson said AI has made writing software much easier, but verifying that it actually works has not become easier. The company posted on October 15, 2026 that its newest release lets agents ship reliable systems.
Testing roots and funding
Antithesis's founders used deterministic simulation testing while developing the distributed database FoundationDB, and founded the company in 2018 to apply the method to other software. In December 2025 the company raised $105 million in a Series A round led by Jane Street.
In January 2026, Replit published its own research pointing out limits of AI-only security checks, saying the same vulnerability was rated differently depending on code phrasing or question style.
Quick answers
What is deterministic simulation testing?
It runs software in a controlled virtual environment and injects faults such as network latency or server and storage failures, while a hypervisor controls execution order, timing and network conditions so a failing run can be reproduced exactly.
Why does Replit use it for AI-generated code?
Replit CTO Louis Chavez said AI models work probabilistically, so results differ between runs and it is very hard to find all software problems that way.
Who leads Antithesis and who invested?
Will Wilson is CEO. In December 2025 the company raised $105 million in a Series A round led by Jane Street.