With last month's addition of 17 new organizations to the Next Generation ACO program, 26% of all Medicare ACOs now participate in a downside-risk model (including the Medicare Shared Savings Program's (MSSP) Track 1+, Track 2, and Track 3), up from 17% in 2017.

While 2018 is shaping up to be a big year for ACOs making the transition to risk, 2019 could be even bigger. In fact, next year 82 ACOs that have been in the MSSP Track 1 since 2013 must either take on downside risk or leave the program. Organizations that haven't decided whether to continue participating face a rapidly approaching application deadline this summer. CMMI will not accept Next Generation ACO applications for 2019, so these organizations should focus on which downside risk MSSP track (if any) makes the most sense for them.