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This was a proof-of-concept implementation of CPython that supports multithreading without the global interpreter lock (GIL). An overview of the design is described in the Python Multithreading without GIL Google doc.

Now that "PEP 703 – Making the Global Interpreter Lock Optional in CPython" has been accepted, this project is not being actively worked on. Development is focused on making Python 3.13 and later releases support running without the global interpreter lock in a configuration called "free-threading".

Please use the "free-threaded" build of Python 3.13. For installation instructions, see https://py-free-threading.github.io/installing_cpython/.