Baseball America lists one of the Pirates' 2015 first-rounders, Ke'Bryan Hayes, as the ninth-best prospect in the Gulf Coast League. As with the list for the Appalachian League, many of the top players are very early recent draftees, so ninth is a respectable showing for Hayes, who's even ranked above a couple guys who were drafted well before he was.
BA notes that Hayes has an advanced approach at the plate and has the potential to hit 20 home runs a season, even though his game isn't currently geared toward power. BA adds that Hayes is below-average on the bases but that he's earned praise defensively.
Hayes was the only Pirates prospect the list, although that's no surprise, since most of the Bucs' other top draft picks skipped the GCL and went to Morgantown.
Hayes posted a .434 OBP in the GCL, a ridiculous figure for an 18-year-old. He struggled a bit after a brief promotion to Morgantown, but that's perhaps to be expected, since he was several years younger than the average player at the level.