McCullers (forearm) threw a 10-pitch bullpen session Saturday, Matt Kawahara of the Houston Chronicle reports.
McCullers had previously done some throwing from the front slope of the mound, but Saturday marked his first time throwing from the top of the bump since he had surgery last June to repair the flexor tendon and remove a bone spur from his forearm. It's a big step, but McCullers is still at least a month away from a rehab assignment, with a return from the 60-day injured list perhaps coming in July if all goes well.