Okert is 1-0 with a 6.75 ERA in 21 1/3 innings out of the Giants' bullpen this year. The 26-year-old has gone 1-0 with a 2.25 ERA in 12 innings for the River Cats in 2017.
Calixte appeared in eight games for San Francisco earlier this season, batting .160 with a double and three RBIs. The 25-year-old utility man was hitting .262 with 13 homers and 41 RBIs in 76 games for Sacramento this season.
Hwang, 29, hit .167 with a home run and three RBIs in 13 games for the Giants. It was his first stint in the Major Leagues.