Announcing Pyrefly is now in Beta 🎉 Pyrefly is a super fast, open source language server and typechecker for Python. We’ve been working closely with our open source community to improve performance, add new features and address bugs. Learn more: https://youtu.be/4o0RLJJ-FAo

🚀 New Blog Post Alert 🚀 Ax, our OS adaptive experimentation platform, uses machine learning to automate and optimize complex experiments. Discover real-world applications of AX across AI, GenAI, infrastructure and even physical engineering. Learn more: https://loom.ly/Djv-f8k

⚡️OSS Project Spotlight⚡️ Below is a powerful resource monitoring tool for Linux that provides deep insights into system performance, including CPU, memory, I/O, and more — all from an intuitive terminal interface. Learn more: https://github.com/facebookincubator/below

🚀 StyleX: Meta’s Open Source Styling Library for CSS at Scale! StyleX is the styling system that combines the best of CSS-in-JS ergonomics with the performance of static CSS—making styling expressive, type-safe, and lightning fast. Link: https://loom.ly/IEnQjTY

Did you know that 63% of AI training models today are built on @PyTorch? When Meta first released the framework, we wanted to support developer experiences for AI researchers. Today, PyTorch helps accelerate the path to AI productization around the world: https://youtu.be/g__HkxDEvCg

🚀 New Podcast Episode Alert! Are you passionate about Python typing or developer experience? Check out the latest episode of @talkpython.fm featuring Pyrefly, Meta’s blazing-fast type checker for Python: https://www.youtube.com/watch?v=P4RKxl_giH4&t=2s

🚀 New on the Meta Engineering blog: Branching in a Sapling Monorepo Discover how Meta solved the tradeoffs between scalability and dev experience by introducing directory branching alongside full-repo branching in Sapling. Read more here: https://loom.ly/GgxCxto

⚡️OSS Project Spotlight⚡️ Captum is an open source library from Meta for model interpretability in PyTorch. It helps developers understand and visualize the decisions made by deep learning models using attribution methods like Integrated Gradients and DeepLIFT. Learn more: https://captum.ai/

🚀 Big news! Today marks the formation of the React Foundation — a new home for React, React Native, JSX, and the broader React ecosystem. Let’s celebrate a new chapter for React and the open web! 🔗 Read more: https://loom.ly/UrW8eeI #React #OpenSource #WebDev #ReactNative

🚀 Introducing OpenZL, a new #opensource, format-aware compression framework! It uses a unique “graph model” for compression, enabling modular, high-performance codecs and a universal decoder - perfect for structured data at scale Link: https://loom.ly/z09xoNw#opensource #DataCompression

How do you make sure your IDE works smoothly when you have more than 20 million lines of python code? 🤔 For devs at Instagram the answer is to use the Pyrefly VSCode extension 👩🏼‍💻 Read our blog about how Pyrefly improves your experience: https://pyrefly.org/blog/2025/09/15/ide-extension/

🔎 Meta Open Source 101🔎 Meet Sapling, Meta’s next-gen source-control system. It’s Git-compatible but designed for massive repos and lightning-fast operations, even at scale. Perfect if you need speed and a smooth developer experience. Learn more 👉 https://sapling-scm.com