Modular Open-Sources the Mojo Compiler and Toolchain Under Apache 2.0

Modular has released the full Mojo compiler, standard library, and supporting tooling as open source under the Apache 2.0 license with LLVM exceptions, ending four years of development behind a closed compiler. The move follows last week’s 1.0 milestone, which brought source stability to the language. Mojo is Modular’s bet on a general-purpose language built to target GPUs, AI accelerators, and other specialized compute using modern compiler research.

The company framed the release as the latest step in a staged opening: it first published the standard library, then hundreds of thousands of lines of Mojo-written kernel code and tooling, and now the compiler itself. Modular’s stated rationale is that a small core design team defines a language’s character while broad community feedback keeps it honest. Builds are managed through Bazel, and developers can either compile the toolchain from source or pull a prebuilt nightly binary to skip the wait.

One notable caveat: despite the source being available, Modular is not yet accepting contributions to the compiler or tooling, citing the need for deliberate handling of contributions in an era of AI-generated code. It plans to open that door by the end of the year. Standard-library contributions, open since 2024, continue as before.