# Creator of Meta's Hack: Your AI Will Always Cheat — Here's How to Stop It

Page: https://stenobird.com/podcast/tech-lead-journal-633005/creator-of-meta-s-hack-your-ai-will-always-cheat-here-s-how-to-stop-it
Text version: https://stenobird.com/podcast/tech-lead-journal-633005/creator-of-meta-s-hack-your-ai-will-always-cheat-here-s-how-to-stop-it.md
Podcast: [Tech Lead Journal](https://stenobird.com/podcast/tech-lead-journal-633005)
Published: 2026-06-08T12:00:00+00:00
Episode link: https://podcasters.spotify.com/pod/show/techleadjournal/episodes/Creator-of-Metas-Hack-Your-AI-Will-Always-Cheat--Heres-How-to-Stop-It-e3kdo19
Audio file: https://anchor.fm/s/265d7c64/podcast/play/121085417/https%3A%2F%2Fd3ctxlq1ktw2nl.cloudfront.net%2Fstaging%2F2026-5-6%2F425616826-44100-2-2847670f63c89.mp3
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JSON: https://stenobird.com/v1/public/podcasts/tech-lead-journal-633005/episodes/creator-of-meta-s-hack-your-ai-will-always-cheat-here-s-how-to-stop-it
Duration seconds: 4697

## Resource

What if your AI coding agent is quietly cheating on your tests — and how do you stop it? Julien Verlaguet, who built the type system Meta used to migrate tens of millions of PHP lines, is now building Skipper: a closed-loop coding agent designed to make AI-generated code verifiably correct, without human intervention. In this episode, Julien Verlaguet, creator of the Hack programming language at Meta and co-founder of SkipLabs, explains why AI agents will always try to cheat — gaming tests, quietly modifying logic while doing something else, and declaring work done when it isn’t. He draws on his experience migrating Meta’s PHP codebase to a statically typed system, drawing sharp parallels between convincing engineers to trust a new type checker and building systems that can trust an LLM. Julien makes the case for spec-driven development with validation layers at every step, where separate AI instances verify correctness and the code-writing agent is locked out of touching tests. He shares the story of an LLM that silently swapped a union for an intersection while splitting a file — a subtle bug that passed all tests — and why no human would ever have made that mistake. He then walks through how Skipper works: you write a spec, hand over control, and a compiler-like agent produces correct, runnable TypeScript without back-and-forth, backed by a sound incremental type system, reachability analysis, and a reactive runtime that applies diffs in milliseconds. He closes with a grounded take on how the developer role is shifting — not disappearing — toward the kind of design, integration, and oversight work that always mattered most. Key topics discussed: Why AI agents will always try to cheat on your tests The union-vs-intersection bug an LLM introduced silently Spec-driven…

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## Transcript

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