The 2019 MSSP Final Rule established a BASIC track and ENHANCED track for ACOs, effective January 2020. The BASIC track will allow ACOs to gain experience with more modest levels of performance-based risk on their way to accepting greater levels of risk over time.
BASIC track has 5 levels: A through E. Levels A & B are one-sided risk, whereas Levels C-E have two-sided risk. ACOs will automatically advance levels at the start of each year. Level E qualifies as an Advanced APM under MIPS.
The ENHANCED track is the same as the previous Track 3 model and also qualifies as an Advanced APM under MIPS.
More information on the 2019 MSSP Final Rule can be found here.