The USA international moves to Palace on a season-long loan.
"I'm really excited to be here,” he told Palace TV. “The last minutes of any deal get a little bit stressful, but it's really good to be here now, and I'm just ready to get to work.
“The Premier League is the best league in the world, so I really want to be here. I really want to challenge myself. I think I learned a lot of lessons, particularly last season.
“I learned what it takes to win in this league. The margins are very fine, and obviously I learned a lot of lessons while I was at Arsenal as well.
“For me, I've grown a lot as a player, a goalkeeper, a person, a father, a husband, and for me, I feel like I'm in a really good place to put my best foot forward and really hit the ground running.”