Python 3.15 First Beta Released – No New Features After This Point

Python 3.15 Beta release

First beta released; no new features will be added after this beta. The final stable version is scheduled for 1 October 2026.

Stable ABI for free‑threaded CPython

Provides a stable application binary interface for extensions compiled for multiple free‑threaded micro‑versions. Only a subset of the full CPython API is available. The existing stable ABI remains usable, allowing extensions to be built for two versions without rebuilding for each minor release.

Explicit lazy import

New lazy keyword enables deferred loading of modules until first use, reducing start‑up time. Two forms are supported: lazy import json – module‑level lazy import; creates a binding that loads json on first access. lazy from json import dumps – name‑level lazy import; loads json only when dumps is first used.

Tachyon sampling profiler

Zero‑overhead sampling profiler that captures stack‑trace samples instead of instrumenting function calls. Documentation claims virtually no overhead and supports sampling rates up to 1 000 000 Hz, making it suitable for production‑level performance debugging.

UTF‑8 default source encoding

Source files are interpreted as UTF‑8 by default; documentation still recommends explicitly specifying the encoding for maximum compatibility.

Improved JIT compiler

Team‑reported benchmarks show average speedups of 8‑9 % on x86‑64 Linux and 12‑13 % on macOS compared with the interpreter, while some workloads may experience up to a 15 % slowdown. These numbers may change before the final release.

Incremental garbage collector removal

The incremental GC introduced in 3.14 was withdrawn after memory‑leak reports and removed in 3.14.5. Re‑introduction in 3.16 would follow the normal PEP process and undergo thorough evaluation.