Commit 9feeaca

Inspired by [py-free-threading.github.io](https://py-free-threading.github.io/) I decided to try out a beta of Python 3.13 with the new free-threaded mode enabled, which removes the GIL.

I chose to use the macOS installer to get a pre-built binary. I downloaded and ran the macOS installer from [www.python.org/downloads/release/python-3130b3/](https://www.python.org/downloads/release/python-3130b3/), and then when I got to this screen:


I selected the "Customize" option and checked this additional box:


Once it had finished installing I didn't run the script to add it to my path (I didn't want to intefere with my many other Python versions).

This gave me two new Python binaries - one with free-threading enabled and one without:

- `/Library/Frameworks/Python.framework/Versions/3.13/bin/python3.13`

- `/Library/Frameworks/PythonT.framework/Versions/3.13/bin/python3.13t`

Note the `PythonT.framework` in the second path.

It also seemed to setup the following aliases in `/usr/local/bin`:

- `/usr/local/bin/python3.13`

- `/usr/local/bin/python3.13t`

These are symlinks:

ls -lah /usr/local/bin | grep python3.13

Starting those Python processes shows which one has free-threading in the interpreter header:

I asked Claude 3.5 Sonnet to write me [a quick test script](https://claude.site/artifacts/92aec50b-43c7-463a-b8a1-5d5ea0600708), then iterated on and simplified the result myself until I got to this:

import argparse

import time

from concurrent.futures import ThreadPoolExecutor

def cpu_bound_task(n):

"""A CPU-bound task that computes the sum of squares up to n."""

return sum(i * i for i in range(n))

def main():

parser = argparse.ArgumentParser(description="Run a CPU-bound task with threads")

parser.add_argument("--threads", type=int, default=4, help="Number of threads")

parser.add_argument("--tasks", type=int, default=10, help="Number of tasks")

parser.add_argument(

"--size", type=int, default=5000000, help="Task size (n for sum of squares)"

)

args = parser.parse_args()

print(f"Running {args.tasks} tasks of size {args.size} with {args.threads} threads")

start_time = time.time()

with ThreadPoolExecutor(max_workers=args.threads) as executor:

list(executor.map(cpu_bound_task, [args.tasks] * args.size))

end_time = time.time()

duration = end_time - start_time

print(f"Time with threads: {duration:.2f} seconds")

if __name__ == "__main__":

main()

I saved this as `gildemo.py` and tried running it with the new Python binaries the one with free-threading enabled and the one without.

Here's what I saw in Activity Monitor while running the scripts:

No free-threading (with the GIL) - reported 99% CPU usage:


Free-threading (no GIL) - reported 258.8% CPU usage:


And here are some results from running the script. First with the GIL in place:

And then without the GIL: