Treinen (shoulder) was activated from the injured list prior to Wednesday's game against the Twins, Martin Gallegos of MLB.com reports.
Treinen made a remarkably quick recovery from a rotator cuff strain, and for what it's worth, he gave up three runs on four hits in one inning in his lone rehab appearance at Triple-A. He will presumably return to being Oakland's closer, but Liam Hendriks may still get the occassional save chance, given how well he has pitched of late.