The Dutch defender joined the Cherries on loan at the start of the 2016-17 campaign, but he was recalled by the Blues in January.
Ake, who can play across the back or in midfield, made just five appearances in all competitions when he returned to Stamford Bridge, but his long-term future remains uncertain.
"At Bournemouth it was all about playing games," Ake told Chelsea's official website. "I played centre-back and I hadn't done that in the Premier League before. I really enjoyed it because they are a good team who play good football.
"When I came back here it was a different challenge, playing with top players, fighting for the title and playing in the FA Cup semi-final. It's been a really good season to look back on and I've learnt a lot on the pitch, as well as becoming more mature off the pitch, it's been really good."
Ake has played for Reading, Watford and Bournemouth since joining Chelsea from Feyenoord in 2011.