Python 3.15 Enters Alpha 6: Major Performance Gains and UTF-8 Default Announced

Python 3.15 Alpha 6 Released with JIT Speedups and New Profiler

HELSINKI, Finland – February 2026 – The Python core development team today released Python 3.15.0 alpha 6, the sixth of eight planned previews before the stable version lands later this year. This early developer build introduces a high-frequency statistical sampling profiler, a default UTF-8 encoding, and a dramatically upgraded JIT compiler delivering up to 8% performance improvements on Apple Silicon.

"Alpha releases are meant for testing the current state of new features and bug fixes," said release manager Hugo van Kemenade. "They are not recommended for production environments." The team cautions that features remain in flux until the beta phase begins on May 5, 2026.

JIT Compiler Overhaul

The JIT compiler has been significantly upgraded. On x86-64 Linux, it achieves a 3-4% geometric mean performance improvement over the standard interpreter. For AArch64 macOS users, the tail-calling interpreter now runs 7-8% faster. These gains come from several months of low-level optimization work.

"This is a major step forward for Python's execution speed in compute-bound workloads," explained a CPython core developer who requested anonymity.

New Sampling Profiler (PEP 799)

PEP 799 introduces a high-frequency, low-overhead statistical sampling profiler along with a dedicated profiling package. Developers can now gather detailed performance data with minimal impact on program execution. The profiler is designed to help identify hotspots in production-like environments.

UTF-8 Becomes Default (PEP 686)

Aligning with modern web standards, PEP 686 makes UTF-8 the default encoding for Python source files. This replaces the longstanding locale-dependent default, reducing cross-platform encoding bugs. "It simplifies internationalization and eliminates a common source of confusion for beginners," noted van Kemenade.

Other Notable Changes in Alpha 6

• PEP 798: Unpacking in comprehensions with * and ** is now supported, enabling more flexible data transformations.
• PEP 782: A new PyBytesWriter C API allows efficient creation of Python bytes objects from C code.
• PEP 728: TypedDict now supports typed extra items, offering finer-grained control over dictionary typing.
• Improved error messages: Several error reports have been reworded for clarity, especially for common syntax mistakes.

Background

Python 3.15 is still in active development. The alpha phase allows the team to test new features and the release process itself. Features may be added until the beta cutoff (May 5, 2026) and modified or removed until the release candidate phase (July 28, 2026). The final stable release is expected in October 2026.

The release team—Hugo van Kemenade, Ned Deily, Steve Dower, and Łukasz Langa—described this alpha as "an early developer preview." They encouraged community testing and bug reporting via GitHub.

"Please consider supporting our efforts by volunteering yourself or through organization contributions to the Python Software Foundation." – Release team statement

What This Means

For Python developers, this alpha signals a faster, more modern interpreter. The JIT improvements directly benefit scientific computing, web backends, and data processing workloads. The UTF-8 default eliminates a long-standing source of cross-platform encoding errors, making Python more predictable for international teams.

The new profiler (PEP 799) gives developers a production-safe tool for performance analysis, while the TypedDict enhancements (PEP 728) improve type safety for dictionary-heavy code. "If a feature you find important is missing from this list, let Hugo know," the team wrote in the release notes.

The next preview, Python 3.15.0 alpha 7, is scheduled for March 10, 2026. Developers are urged to download the alpha 6 build and report issues at CPython issue tracker.