Engineering at Meta (@Meta_Engineers)

🧠Forum, Meta’s new standalone Groups app, was built by a small team that brought an AI agent into the development cycle as a participant — planning, building, testing, and verifying. Building Forum we moved from human-in-the-loop — engineer drives, AI assists inside each step — to human-on-the-loop, where the agent runs the iteration (plan, implement, build, test, correct, repeat) and the engineer sets the goal, watches the run, and owns the outcome. The key decision: success wasn’t measured in code volume. It was measured in changes that build, pass tests, and survive review. ✅ Reached core feature parity with Facebook Groups in eight weeks 📈 An autonomous stress-testing loop caught a memory issue during development, roughly halving memory use and page faults 🔗 Read how our engineers went AI-native to build Forum: #AI# #SoftwareEngineering# #DeveloperTools# #MobileEngineering# #Engineering#

🧠 Most AI bug-catching tools review your code the way a human reviewer would, only faster. What if the AI wrote a test that proved the bug instead? That’s Catching Just-in-Time Tests (JiTTests) — a novel approach where LLMs generate executable tests designed to fail, surfacing behavioral changes in a code change before it lands. After a year of research, it’s now part of Meta’s infrastructure. ✅ 589 engineers have engaged with it, reporting a 60% true-positive rate 📈 In the first half of 2026, it helped catch 74 privacy SEVs at the diff stage, lowering overall privacy SEV occurrence by 20% 🔗 Read how it works: 📄 Read our FSE 2026 paper, “Just-in-Time Catching Test Generation at Meta”: #AI# #SoftwareEngineering# #SoftwareTesting# #DeveloperTools# #Engineering#