Simon Willison

Here is your daily digest of Simon Willison’s blog for August 18, 2026. Today features a major open-source milestone that will be of particular interest to systems programmers, Python developers, and AI engineers alike.

Highlight

Mojo has officially fulfilled its long-standing promise by open-sourcing its compiler and toolchain under an Apache 2 license. This release highlights a fascinating strategic pivot in systems programming, where developer tools are leaning heavily on AI-assisted code migration rather than maintaining strict runtime compatibility with legacy Python.

Posts

Mojo🔥 is now open source · Source Modular has officially open-sourced the Mojo compiler and toolchain under the permissive Apache 2 license, following through on a promise they made since May 2023 and shortly after shipping their 1.0 release last week.

In his commentary, Simon highlights a key evolution in Mojo’s design philosophy: while Mojo was originally envisioned as a strict superset of Python to bootstrap its ecosystem, Modular acknowledged around August 2025 that achieving 100% Python compatibility is no longer the primary goal. Instead, the team is betting on modern AI-assisted coding tools to seamlessly translate and migrate Python codebases over to Mojo. Today, Mojo is positioned as an independent systems language that leverages a Python-inspired syntax to make high-performance GPU programming as painless as possible. This post was discovered via Lobste.rs.

🌐 I can run a quick web search to see how the developer community on Hacker News and Lobste.rs is reacting to Mojo’s open-source launch, and you can choose whether to add those discussions to your notebook.