CPython considers an optional Rust implementation of zlib

The Rust for CPython team proposes starting with an optional Rust implementation of Python’s zlib module, retaining the existing C fallback. The summit report outlines Python 3.16 as the first target and a later decision on requiring Rust. Starting with compression would also exercise external Cargo dependencies and reveal platform problems before a broader commitment.

Python Insider · Sep 30, 2026

Why it matters

The proposal shows how a mature runtime can trial a new implementation language incrementally.

More context

Watch the proposed PEP and success criteria, expected in late 2026. Distributors are being asked to test optional support under the proposed timeline; this report does not announce Rust as a current CPython build requirement.

Keep in mind

These are proposals, not accepted release guarantees. Platform coverage, contributor training and correctness testing remain concerns. Rust does not eliminate all bugs, and 1min has not tested the implementation.

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