Maxon 0.2.0

Sep 14, 2026

Maxon 0.2.0 is released. Archives for every supported target are on the GitHub releases page.

What changed

One-line installers for macOS, Linux and Windows, which install the latest release into ~/.maxon.
maxon upgrade, which updates the install the running compiler belongs to.
Container images at ghcr.io/maxon-lang/maxon, in debian and distroless variants for amd64 and arm64.
The Homebrew formula serves x64 and arm64 Linux as well as macOS.
maxon mcp-server, a Model Context Protocol server exposing build, run, test, format, check, IR dumps and error-code lookup to AI tools.

A green thread that runs for 10 ms without waiting is preempted, including inside a loop that calls nothing, so one busy thread no longer holds up the others.
Socket reads, accepting a connection, subprocess pipes and waiting for a child process park only the green thread that waits; none of them occupies an OS thread any more.
main runs as a green thread whose stack grows as needed, and idle green threads give back stack they no longer use.
Mutating a value that a live let can still observe is refused, however the value was reached — through a call’s result, a closure, an interface method or a union payload as well as a direct field. A write through a method or a field that could reach such a record is a new error, E3159.
Generated code is substantially faster: every function called from one place is inlined, and the optimizer gains value-range analysis, bounds-check elimination against loop limits, loop unswitching, jump threading and hot/cold code layout. fannkuch-redux runs in about 1.2× the time of the C reference, down from 5.4×.
A stack trace names inlined functions as their own frames, and prints up to 100 frames, saying when it stops short.
The compiler runs its per-function optimization passes and instruction selection in parallel.
On Windows, a compiled program’s file description is its own name; the “Built with Maxon” credit is in its Comments field.

maxon build intermittently hung on macOS when a build manifest ran subprocesses.
Deep recursion in main overflowed its stack at 1 MB on Windows.
A function returning a tuple of two records could hand back a freed record.
Passing a struct that holds a file or socket to an async call crashed the compiler.
A fault on arm64 macOS with a corrupted stack hung instead of printing a trace, and a fault on a Windows green thread printed its report twice.
maxon run failed in deeply nested directories on Windows.

To install Maxon or upgrade an existing install, see Installation, which also shows how to install a specific release.