State of Python 3.13 Performance: Free-Threading

CPython 3.13 was released two weeks ago and this release is the most performance-oriented in some time. After a quick read of the release notes, a few things stand out for the impact they can have on the performance:

Let's focus on the free-threaded mode in this article to see how to leverage this change and how it can impact the performance of Python applications by measuring performance with CodSpeed.

Free-threading is an experimental feature in Python 3.13 that allows CPython to run without the Global Interpreter Lock (GIL). The GIL is a mutex preventing multiple threads from executing Python bytecode simultaneously. This design choice has simplified CPython's memory management and made the C API easier to work with. However, it has also been one of the most significant barriers to utilizing modern multi-core processors effectively.

The traditional solution has been to use the multiprocessing module, which spawns separate Python processes instead of threads and while this approach works, it comes with significant limitations:

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