Python 3.14 released with cautious free-threaded support

"Free threading in Python, which disables the global interpreter lock (GIL), is now a complete implementation of PEP (Python Enhancement Proposal) 703, a much anticipated feature which makes concurrent programming in Python natural. Free-threaded mode also enables a specialized adaptive interpreter, originally part of the Faster CPython project led by Mark Shannon at Microsoft (though the company axed its support in May)."

"That said, the approach to free-threaded Python remains cautious. The big problem is that existing code may break (particularly when using the C API since it is the application binary interface, or ABI, that is not compatible), and a second issue is that single-threaded code runs between 5 to 10 percent slower when using the free-threaded interpreter."

"The consequence is that although free-threaded Python is now fully supported, the free-threaded interpreter is not installed by default. On the Mac, the installer requires it to be selected as a customized install, and on Windows, using a new preview Python install manager from the Windows Store, the user needs to add the free-threaded install using: py install 3.14t. Once installed, the free-threaded build must be specified with a command such as python3.14t, otherwise the single-threaded build will run."

Version 3.14 implements PEP 703 to provide free threading by disabling the GIL and enabling more natural concurrent programming. Free-threaded mode also activates a specialized adaptive interpreter from the Faster CPython project. Compatibility risks exist because the C API/ABI can break existing extensions, and single-threaded workloads may slow by 5–10% under the free-threaded interpreter. The free-threaded build is optional and not installed by default; installers on macOS require a customized selection and Windows users must add the preview install (py install 3.14t) and invoke python3.14t. Additional features include template string literals, multiple interpreters in one process, and a new attachable debugger interface, plus an opt-in interpreter with a 3–5% performance boost.

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