“The performance degradation when Python is built with free-threading support is significant – around 20%.”
Python 3.13 ships a build without the GIL and an experimental JIT. The free-threaded build costs around 20% on single-threaded code, and importing one module that needs the GIL quietly turns it back on. The JIT changes nothing for now. Python finally lets you use all your cores, and charges a fifth of one for the privilege.