Python 3.15.0rc1 has been released as the first release candidate, featuring significant updates such as lazy imports, a built-in frozendict, and the new Tachyon profiler. The lazy keyword allows for deferred module loading, potentially improving startup times by up to 70% in large codebases, while frozendict is a new immutable dictionary type. The profiling package has been revamped, introducing the Tachyon sampler for high-frequency statistical profiling and supporting various output formats. Additional changes include JIT compiler speed improvements, new PEPs for advanced features, and multiple deprecations, with the final version of Python 3.15 targeted for October 2026
Python 3.15.0rc1 Released: Lazy Imports, Built-in frozendict, and Tachyon Profiler
Python 3.15.0rc1 is now available as the first release candidate in a two-RC cycle, with the final version targeted for October 2026. The release is headlined by PEP 810's lazy keyword for deferred module loading, which the team reports can reduce startup times by up to 70% on large codebases at companies like Meta. Additional major changes include a built-in frozendict type, a new profiling package featuring the high-frequency Tachyon sampler, and JIT speedups ranging from 8% to 13% depending on the architecture. Developers and maintainers should test against rc1 now, as binary wheels built against this candidate will be ABI-stable for the final release.
