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Radar · Rust · #002 · Week 40 · Sep 28 – Oct 4, 2026

Rust 1.99.0 released

Worth knowingtooling

What changed
The Rust team announced the availability of version 1.99.0 and pointed to the release notes.
Production impact
The source does not say.
Try it
Run rustup update stable on a machine with a previous stable toolchain and verify the version with rustc --version.
Source
blog.rust-lang.org/2026/10/01/Rust-1.99.0/

Understand it, then run it

Rust 1.99.0 adds the ability to write C‑style variadic functions directly in Rust. Before this release you could only call variadic functions that were already written in C, such as printf. The new feature lets you define a function that takes a variable number of arguments using the ... syntax and work with a VaList value inside the function.

To use it you write an unsafe extern "C" function, read arguments from the VaList with next_arg::<T>(), and then return a result. The change is limited to the "C" and "C-unwind" ABIs; other ABIs still require inline assembly.

Written by gpt-oss-120b from the linked source · claims checked against the sources · human-reviewed