Gentoo Developer Asks Python Projects to Drop uv-build

Michał Górny, a Gentoo developer, asked Python projects on Oct. 12 to stop using uv-build, the Rust-based build backend from Astral's uv, in a blog post titled "A plea not to use uv-build." He wrote that the post is not a criticism of uv or other Astral tools, only of the backend, whose drawbacks he says outweigh its benefits.

A build backend is the program that turns a source tree into a wheel or source distribution. Under PEP 517, any installer such as pip or uv can call any backend, so a project's choice of backend is a decision about everyone who builds it from source.

The numbers in the post

As of uv-build 0.13.0, Górny wrote, the wheels are 1.2 to 1.5 MiB depending on platform. The flit-core wheel is about 45 KiB. He counted 12 uv-build releases in the 30 days before the post.

For Gentoo, which builds packages from source, each release means compiling a Rust tool again. He said packages lose their stability keywords when a key dependency switches to uv-build.

1. flit-core45 KiB
2. uv-build, smallest wheel (1.2 MiB)1229 KiB
3. uv-build, largest wheel (1.5 MiB)1536 KiB

Source: Michał Górny, Gentoo blog, Oct. 12, 2026 (uv-build 0.13.0; MiB converted at 1,024 KiB)

Why Rust is the sticking point

Górny's portability case is specific. Rust supports fewer platforms than C, he wrote, so uv may fail even where a Rust compiler exists. His examples are a rustix dependency that skips SPARC, and binaries so large they exhaust address space on 32-bit platforms. The Gentoo uv ebuild, the package's build recipe, already carries two workarounds for 32-bit builds.

He dismissed the two usual arguments for the backend. Consistency with uv does not matter under PEP 517, he wrote. The speed gain is roughly 100 ms for an action that runs rarely, and fetching a 1.5 MiB wheel can offset it.

His complaint is about packaging, not the language's safety record, which this site covered in a report on a borrow-checker bug open for 11 years.

What Astral's documentation says

Astral's build backend documentation calls uv_build "a great choice for most Python projects." It also states that the backend "currently only supports pure Python code", which is the case Górny says gains nothing from Rust.

The page says the backend follows uv's versioning policy and recommends pinning an upper bound, for example uv_build>=0.13.0,<0.14, so a package keeps building as releases arrive.

The uv executable also bundles a copy that it uses for its own builds when the version is compatible. Other frontends, such as python -m build, always fetch the uv_build package from PyPI.

Backend	Language	Wheel size	Named by
uv-build 0.13.0	Rust	1.2 to 1.5 MiB	Górny
flit-core	Python	about 45 KiB	Górny

What he asks maintainers to use

Górny names two pure-Python backends, flit-core and hatchling, and says both work with uv and other frontends. Astral's documentation itself points to hatchling for projects that need build scripts or a more flexible layout.

Build tooling choices get argued on figures the vendor supplies, as in the Scion source control story, where Anthropic's numbers were all its own. Here the figures are a packager's, and the post does not name which projects have adopted uv-build, so how many Gentoo packages are affected is unknown.

The number to watch is the release count. Górny counted 12 uv-build releases in 30 days, and the pin in Astral's example, <0.14, closes at the next minor version.