we are passing

--python-setup-resolver-cache-dir

to a directory that is shared between the 8 CI worker processes running on each box and is not cleaned out between runs, but maybe that option changed?

Circling back to this detail,

--python-setup-resolver-cache-dir

is still used so even though we're falling through Pants

[cache]

reads and continuing to resolve, the resolve itself should be hitting the resolver cache ultimately used by pex. It may just be that the overhead still left is large compared to the prior python stack in <1.3.0. That older stack avoided re-building python chroots - and re-resolving, using

--python-setup-chroot-cache-dir

. The new stack does not use that option. Were you perchance also sdetting that option to a global dir in CI?

nope