Python 3.15 Alpha 6 Released: New Profiler, UTF-8 Default, and JIT Speedups

Introduction

The Python development team has announced the sixth alpha release of Python 3.15, version 3.15.0a6. This is an early developer preview intended to help test new features and bug fixes before the beta phase begins on May 5, 2026. As an alpha release, it is not recommended for production environments, but it offers a glimpse into the changes coming in the 3.15 series.

New Features in Python 3.15 Alpha 6

Python 3.15 is still under active development, and several major new features have already been introduced. Here are the key changes so far:

PEP 799: High-Frequency Statistical Sampling Profiler

A new profiler is being added, designed for low overhead and high-frequency sampling. It will be part of a dedicated profiling package, making it easier for developers to optimize their code without significant performance impact.

PEP 798: Unpacking in Comprehensions

This PEP allows the use of * and ** unpacking operators within comprehensions, providing more concise syntax for certain patterns.

PEP 686: UTF-8 as Default Encoding

Python will now use UTF-8 as the default encoding, aligning with modern standards and simplifying cross-platform text handling.

PEP 782: PyBytesWriter C API

A new C API, PyBytesWriter, will enable efficient creation of Python bytes objects from C code, improving performance for extensions.

PEP 728: TypedDict with Typed Extra Items

TypedDict gains the ability to specify typed extra items, enhancing type safety for dictionaries with known and unknown keys.

JIT Compiler Upgrades

The Just-In-Time (JIT) compiler has received significant enhancements. Benchmarks show a 3-4% geometric mean performance improvement on x86-64 Linux over the standard interpreter, and a 7-8% speedup on AArch64 macOS compared to the tail-calling interpreter. These gains mean faster execution for many Python programs.

Improved Error Messages

Error messages have been refined to be more informative and helpful, aiding developers in debugging their code more quickly.

Upcoming Release Schedule

The next pre-release will be Python 3.15.0a7, currently scheduled for March 10, 2026. After eight alpha releases, the beta phase will begin, followed by release candidates and the final release.

Resources and Community

For more information, visit the online documentation and check the PEP 790 release schedule. Bugs can be reported on the CPython issue tracker. The Python Software Foundation welcomes financial support via direct donations or GitHub Sponsors.

Conclusion

Python 3.15 alpha 6 marks another step forward for the language, with promising new features and performance improvements. Developers are encouraged to test the preview and provide feedback to help shape the final release. As always, the release team thanks the countless volunteers who contribute to Python's success.