Python 3.15 Alpha 6 Released—JIT Speed Gains Up to 8%

The Python Software Foundation has released Python 3.15.0 alpha 6, the sixth of eight planned alpha releases for the upcoming 3.15 series. This developer preview brings significant performance improvements and several new features, including a statistical profiler and enhanced error messages.

“This alpha release is a critical milestone for testing the new JIT compiler and other changes,” said Hugo van Kemenade, the release manager for Python 3.15. “We’re seeing a 3-4% geometric mean performance improvement on x86-64 Linux over the standard interpreter, and up to 7-8% speedup on AArch64 macOS compared to the tail-calling interpreter.”

Major Performance Gains with JIT Compiler

The JIT (Just-In-Time) compiler has undergone a substantial upgrade in this release. The improvements deliver measurable speedups across two major platforms, making Python 3.15 a compelling choice for performance-sensitive applications.

The alpha also includes better error messages, which aim to help developers diagnose issues more quickly during debugging.

New Features and PEPs

Among the major new features introduced so far in the 3.15 series:

• PEP 799 — A new high-frequency, low-overhead statistical sampling profiler and dedicated profiling package.
• PEP 798 — Unpacking in comprehensions with * and **, expanding expression capabilities.
• PEP 686 — Python now uses UTF-8 as the default encoding, aligning with modern text handling.
• PEP 782 — A new PyBytesWriter C API to create Python bytes objects more efficiently.
• PEP 728 — TypedDict now supports typed extra items, improving static type checking.

For a full list of changes, refer to the Background section or the official release notes.

Background

Python 3.15 is still in active development. Alpha releases like this one are designed to allow early testing of new features and bug fixes before the beta phase begins. The beta phase is scheduled to start on 2026-05-05, and the first release candidate will follow on 2026-07-28.

“Alpha releases are intended to make it easier to test the current state of new features and the release process,” van Kemenade explained. “Please keep in mind that this is a preview release and its use is not recommended for production environments.”

What This Means

For Python developers and early adopters, this alpha release provides a first look at the performance gains from the upgraded JIT compiler. The new statistical profiler (PEP 799) will help identify bottlenecks in long-running applications without significant overhead.

The default UTF-8 encoding (PEP 686) simplifies internationalization, while improvements to comprehensions and TypedDict enhance expressiveness and type safety. The PyBytesWriter API offers a lower-level path for C extension authors to build bytes objects.

Overall, the 3.15 alpha 6 release signals a strong focus on performance and developer experience ahead of the beta freeze. Developers working on libraries, frameworks, or performance-critical code are encouraged to test this release and report any regressions.

Looking Ahead

The next pre-release of Python 3.15 will be 3.15.0a7, currently scheduled for 2026-03-10. The release team has asked core developers to contact Hugo van Kemenade if any important features are missing from the current list.

“Thanks to all the volunteers who help make Python development and these releases possible,” van Kemenade concluded. “Please consider supporting our efforts by volunteering or through organizational contributions to the Python Software Foundation.”

More resources: Download Python 3.15.0a6 | Release schedule (PEP 790) | Report bugs