Python 3.15.0 RC1 Released with New Features and Performance Improvements

Python 3.15.0 Release Candidate 1 (rc1) is the first candidate release for Python 3.15. This release enters the RC phase, meaning only reviewed bug fixes will be considered for inclusion before the final release. No ABI changes will occur from this point forward in the 3.15 series.

Python 3.15 introduces several major features, including explicit lazy imports (PEP 810), a new frozendict built-in type (PEP 814), a sentinel built-in type (PEP 661), and a dedicated profiling package (PEP 799). Other additions include enabled frame pointers by default for observability, unpacking in comprehensions, UTF-8 as the default encoding, package startup configuration files, and typed TypedDict with extra items.

The JIT compiler has been substantially upgraded, resulting in an estimated 8-9% performance improvement on x86-64 Linux and 12-13% on AArch64 macOS. Official Windows 64-bit binaries now utilize the tail-calling interpreter, and macOS binaries include free-threading support by default.

This release includes enhancements to error messages for better clarity and increased use of color in the output, aiming to improve the developer experience.

Maintainers of third-party Python projects are encouraged to prepare for Python 3.15 by publishing Python 3.15 wheels on PyPI. Binary wheels built against release candidates will be compatible with future 3.15 versions.

This is a preview release and not recommended for production. Users are urged to report any issues found to the Python bug tracker. Core team members are reminded to ensure all changes are properly documented and updated in 'What's New'.