Meta Open Source

We’re thrilled to share that Pyrefly, our open source type checker and language server for Python, has officially reached v1.0! This has been a huge team effort. Since our beta release last November, we've shipped over 60 updates, fixed hundreds of bugs, and added features the community has been asking for. Check out our latest video and blog walking through what you can expect from the latest release: Video: youtube.com/watch?v=_o0TZG… 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. The survey is a joint initiative developed by the Python Software Foundation and JetBrains. Link: surveys.jetbrains.com/s3/python-deve…

⚡️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. yogalayout.dev

⚡️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: 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: pyrefly.org/blog/type-narr…

Once the build finishes, Infer outputs a list of potential issues directly in your console and generates a detailed infer-out/ directory. It’s used at scale at Meta to analyze code changes every day. Read the full engineering deep dive here: engineering.fb.com/2017/09/06/and…

Using it is surprisingly simple. You don't need to change your code—just prefix your usual build command with infer run --. For example: • Gradle: infer run -- ./gradlew build • Maven: infer run -- mvn compile • Make: infer run -- make

🔎 Meta Open Source 101🔎 Want to catch null pointer exceptions and resource leaks before they crash your app? Use Infer, a static analyzer that works by wrapping your build command to detect complex bugs in Java, C++, and Objective-C. Get started: 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: 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: engineering.fb.com/2025/12/22/dev…

🔎 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: ai.meta.com/research/publi…

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: 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: engineering.fb.com/2025/11/18/ope…

⚡️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: github.com/facebookincuba…

🚀 StyleX: 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: engineering.fb.com/2025/11/11/web… #OpenSource #CSS

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: youtu.be/g__HkxDEvCg

🚀 New Podcast Episode Alert! Are you passionate about Python typing, developer experience or IDE tooling? Check out the latest episode of Talk Python To Me featuring the team behind Pyrefly, Meta’s blazing-fast type checker and language server for Python youtube.com/watch?v=P4RKxl…

🚀 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: engineering.fb.com/2025/10/16/dev…