If you look at the code he used to test this, its completely CPU-bound, meaning that it requires the GIL to run. And since the GIL is, well, a "GIL," that means that only one can run at any single time.<p>Therefore, the expected behavior of running these two threads would be to have identical runtimes. That would be the "perfect" case with a GIL. So with this "better" GIL its actually near-perfect in this _simple_ case. (Like the presenter said, there needs to be more tests to study the behavior under heavier tasks)<p>What you're describing, with the threaded being "twice as fast" assumes that the threads will allow two python-instruction-bound tasks to run concurrently, which would require having no GIL.