Gattis, 28, hit .263 (97x369) with 17 doubles, 22 homers, 52 RBI and a .493 slugging percentage in 108 games for the Braves last season. Gattis has hit more than 20 homers in each of his two Major League seasons while slugging .487 over that span.
Last season, the Astros ranked third in the American League with 163 homers, their most since hitting 167 in 2008.
Hoyt, 28, has been invited to Astros Spring Training as a non-roster invitee. In three minor league seasons, the right-hander has gone 6-6 with a 3.61 ERA (57ER/142IP), 182 strikeouts and a .212 opponents' batting average. Last season, he appeared in 24 games at Triple A Gwinnett and 28 games at Double A Mississippi. While with Mississippi, he was named a Southern League Midseason All-Star after going 2-2 with a 1.14 ERA (4ER/31.2IP), 43 strikeouts, 10 walks and a .170 opponents' average.
Foltynewicz, 23, was a first round pick by the Astros in 2010 (19th overall) and made his Major League debut with the club last season, pitching in 16 games out of the bullpen. He spent the majority of the 2014 season at Triple A Oklahoma City, where he struck out 102 batters in 102.2 innings pitched over 21 games (18 starts).
Ruiz, 20, hit .293 (151x516) with 37 doubles, 11 homers, 77 RBI and a .387 on-base percentage at Class A Advanced Lancaster last season. The third baseman was originally a fourth round pick by the Astros in the 2012 draft.
Thurman, 23, made 26 appearances (20 starts) for Class A Quad Cities in 2014, winning seven games while striking out 107 batters in 115.1 innings pitched. The 2014 season was his first full-year in the Astros system, as he was a second round pick by the club in the 2013 draft.