Python 3.15 Alpha 6 Released: JIT Compiler Gets Major Speed Boost, New Profiler Unveiled
The Python development team has unleashed the sixth alpha of Python 3.15, bringing a statistical sampling profiler and a revved-up just-in-time (JIT) compiler. This preview release, 3.15.0a6, is the sixth of eight planned alpha releases and is now available for early testing by developers. Read on for background and what this means for developers.
Key New Features in Python 3.15
- PEP 799: A new high-frequency, low-overhead statistical sampling profiler and dedicated profiling package.
- PEP 798: Unpacking in comprehensions using
*and**. - PEP 686: Python now defaults to UTF-8 encoding.
- PEP 782: A new
PyBytesWriterC API for creating bytes objects. - PEP 728:
TypedDictwith typed extra items. - JIT compiler upgrade: 3-4% geometric mean speedup on x86-64 Linux over the standard interpreter, 7-8% on AArch64 macOS over the tail-calling interpreter.
- Improved error messages for sharper debugging.
Quote from Release Manager
“Alpha releases are intended to make it easier to test the current state of new features and bug fixes,” said Hugo van Kemenade, the release manager. “Features may be added up until the start of the beta phase on 2026-05-05, and may be modified or deleted up until the release candidate phase on 2026-07-28.”
Background
Python 3.15 remains under active construction. This alpha release is strictly for development testing and should not be used in production environments. The release cycle follows the typical Python cadence: multiple alpha, beta, and release candidate stages before the final stable version.
The new PEP 799 profiler aims to provide a lightweight way to sample running code, letting developers pinpoint performance hotspots without heavy overhead. The JIT enhancements continue the work begun in Python 3.13, which first introduced a basic JIT compiler. Additional PEPs tackle unpacking in comprehensions and default UTF-8 encoding (PEP 686), aligning Python with modern Unicode conventions.
What This Means for Python Developers
Developers can now test these features in their own codebases. The statistical profiler will help identify bottlenecks, while the JIT speedups promise smoother execution, especially on macOS ARM machines. The UTF-8 default encoding (PEP 686) simplifies cross-platform text handling. “We encourage the community to download, test, and report any issues,” van Kemenade added.
Next Steps and Schedule
The next pre-release, Python 3.15.0a7, is slated for 2026-03-10. All alpha releases are available for download at python.org. Developers can also review the full release schedule in PEP 790.
How to Contribute
The Python Software Foundation welcomes contributions and financial support. Bugs can be reported on GitHub at github.com/python/cpython/issues. “Thanks to all of the many volunteers who help make Python development possible,” van Kemenade said in a statement.
Use this alpha release to prepare for the final Python 3.15, which promises richer tooling and better performance out of the box.