The key enabling tech is thread safe reference counting. There are many other problems that Sam Gross solved in order to make it happen but the reference counting was one of the major blockers.
Does it eliminate the need for a GC pause completely?
https://peps.python.org/pep-0703/#reference-counting
If by GC you mean the cyclic GC, free-threaded Python currently stops all threads while the cyclic GC is running.