Simon Willison’s Weblog

In Python 3.14, I have implemented several changes to fix thread safety of asyncio and enable it to scale effectively on the free-threaded build of CPython. It is now implemented using lock-free data structures and per-thread state, allowing for highly efficient task management and execution across multiple threads. In the general case of multiple event loops running in parallel, there is no lock contention and performance scales linearly with the number of threads. [...]

For a deeper dive into the implementation, check out the internal docs for asyncio.

— Kumar Aditya, Scaling asyncio on Free-Threaded Python