We’re thrilled to share that Pyrefly, our open source type checker and language server for Python, has officially reached v1.0! Video: www.youtube.com/watch?v=_o0T... Blog: pyrefly.org/blog/v1.0/ We also want say a huge thank-you to the open-source community for helping us get here. 🙏

The official Python Developers Survey is currently open 📝 🙌 Take the survey now — it takes less than 15 minutes to complete and helps the open source community understand the evolving needs of Python users. Link: surveys.jetbrains.com/s3/python-de...

⚡️OSS Project Spotlight⚡️ Yoga is a cross-platform layout engine that brings Flexbox to any environment—not just the web. It powers the layout for massive frameworks like React Native, enabling you to build responsive UIs once and run them anywhere. www.yogalayout.dev

🔎 Meta Open Source 101🔎 Need to compress data in real-time without sacrificing speed? Use Zstandard (zstd), a fast compression algorithm designed to provide high compression ratios while maintaining incredibly fast encoding and decoding. Get started: https://facebook.github.io/zstd/

⚡️OSS Project Spotlight⚡️ Fairchem is a centralized repository from FAIR Chemistry that provides state-of-the-art data, models, and tools for materials science and quantum chemistry. It includes several datasets to accelerate renewable energy research. https://fair-chem.github.io/

🔎 Meta Open Source 101🔎 Do you work with survey data that doesn't quite match your target audience? Use Balance, a Python package that adjusts biased data samples (like non-representative surveys) by creating weights to match a target population. https://import-balance.org/

⚡️OSS Project Spotlight⚡️ Folly is a library of C++ components designed with practicality and efficiency. It complements the standard library with optimized utilities—such as fast synchronization primitives and memory-efficient containers. Learn more: https://github.com/facebook/folly

🔎 Meta Open Source 101🔎 Need speed of a dynamic language but the discipline of a static one? Meet HHVM (HipHop Virtual Machine) and Hack, the engine and language designed to execute PHP code with lightning-fast performance using JIT compilation. Link: https://hhvm.com/

⚡️OSS Project Spotlight⚡️ Lexical is an extensible text editor framework designed for reliability, accessibility, and performance. It provides a powerful, framework-agnostic engine for building sophisticated text editing experiences on both the web and iOS. Learn more: https://lexical.dev/

New Meta Open Source Content 🔎 Four type-narrowing patterns that make Python type checking more intuitive. 🐍✨ From tuple length narrowing to hasattr guards, see how Pyrefly helps reduce the need for explicit casts in your code. Learn more here: https://pyrefly.org/blog/type-narrowing/

🔎 Meta Open Source 101🔎 Want to catch null pointer exceptions and resource leaks before they crash your app? Use Infer, a static analyzer that detects complex bugs in Java, C++, and Objective-C. Learn more at https://fbinfer.com/

⚡️OSS Project Spotlight⚡️ IGListKit is a data-driven UICollectionView framework for building fast lists on iOS. It features a decoupled diffing algorithm that handles updates automatically, eliminating reloadData or performBatchUpdates. Learn more: https://instagram.github.io/IGListKit/

Python typing is trending — and the community has spoken! 📊 From improved readability to better tooling support, see what developers love (and struggle with) in 2025: https://engineering.fb.com/2025/12/22/developer-tools/python-typing-survey-2025-code-quality-flexibility-typing-adoption/

🔎 Check out our new video on Pyrefly’s Pydantic support Pyrefly currently offers experimental support for Pydantic, bringing improved static type checking and IDE integration to your data models. ▶️ Watch the video: youtu.be/zXYpSQB57YI #Python #TypeChecking #OpenSource

🚀 New from Meta AI Research: Souper-Model! By smartly averaging multiple model weights using a method called SoCE (Soup Of Category Experts), the team achieved strong performance without retraining a whole new model. Read more here: https://loom.ly/bSbrL70

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