Free-threaded Python is no longer experimental

The free-threaded Python build is now officially supported as of Python 3.14 (October 2025), with PEP 779 setting the promotion criteria. The single-threaded penalty has shrunk to roughly 5–10%, and Python 3.15 added a stable abi3t ABI for extensions.

• The free-threaded build (3.14t) lets threads run Python bytecode in parallel across cores
• Single-threaded code runs 5–10% slower than the standard build
• Python 3.15 added a stable abi3t ABI for free-threaded extensions
• The build stays opt-in and needs separately built wheels