Python 3.15.0rc1 is now available – the first of two planned release candidates for the 3.15 line. With this milestone, the ABI is frozen and only reviewed, clearly safe bug fixes are allowed until the final 3.15.0.
The next stop on the schedule is 3.15.0rc2 on 2026‑09‑01, followed by the stable 3.15.0 release.
Why embedded and tooling folks should care
If you rely on Python for build systems, test automation, firmware toolchains or CI around your embedded projects, this is the phase to validate 3.15 compatibility:
- Any binary wheels built against 3.15.0 release candidates will work with future 3.15.x versions;
- 3.15.0rc1 is still a preview and not recommended for production, but ideal for CI and pre‑deployment testing;
- Maintainers are strongly encouraged to publish Python 3.15 wheels on PyPI and report issues via the CPython bug tracker.
Core developers are also reminded to finish and polish documentation, especially entries for the What’s New in Python 3.15 page.
Highlights of Python 3.15
Compared to 3.14, Python 3.15 brings a long list of notable changes:
- PEP 810 – explicit lazy imports for faster startup times;
- PEP 814 – new
frozendictbuilt‑in type; - PEP 661 – new
sentinelbuilt‑in type; - PEP 799 – dedicated profiling package plus Tachyon, a high‑frequency statistical sampling profiler;
- PEP 831 – frame pointers enabled by default for better system‑level observability;
- PEP 798 – unpacking in comprehensions;
- PEP 686 – UTF‑8 is now the default encoding;
- PEP 829 – package startup configuration files;
- PEP 728, 747, 800 – richer typing features (TypedDict extras, TypeForm, disjoint bases);
- PEP 782 – new
PyBytesWriterC API; - PEP 803, 820, 793 – stable ABI for free‑threaded builds and related C API.
The JIT compiler has been significantly upgraded, delivering about 8–9% geometric‑mean speedup on x86‑64 Linux vs. the standard interpreter and 12–13% on AArch64 macOS vs. the tail‑calling interpreter.
Official Windows 64‑bit builds now use the tail‑calling interpreter, and official macOS builds ship with free‑threading support enabled by default. Error messages have also been improved and made more readable (with more color).
For full details, check the online docs and What’s New in Python 3.15, and consider supporting the Python Software Foundation if your projects depend on Python.
Source: Python Insider
