Python language changes that first shipped in something besides CPython?

[Paul Rubin]

Terry Reedy <tjreedy at udel.edu> writes:
> For that type of feature, I am pretty sure the answer is no. There are
> developers from other implementations that have cpython commit rights
> and they have contributed new tests. Modules? I have never seen 'We
> first did this with xpython on the tracker, but it is possible.

What about Stackless?  Maybe some version of generators first appeared there?