What the rule covers
California's Advanced Clean Trucks (ACT) regulation is a zero-emission-vehicle sales requirement for truck manufacturers, plus a one-time reporting requirement for large entities and fleets. It does not require carriers to file an annual fleet inventory or ZEV procurement plan.
Source: California Air Resources Board, Advanced Clean Trucks: https://ww2.arb.ca.gov/our-work/programs/advanced-clean-trucks
California rules that do apply to trucks on the road
With few exceptions, all diesel vehicles over 14,000 lbs GVWR operating in California, including out-of-state vehicles, must have a 2010 or newer engine and emission system (CARB Truck and Bus Regulation).
Under CARB's Clean Truck Check program, subject vehicles operating in California, including those registered in other states, must be reported, pay an annual vehicle compliance fee and submit passing emissions tests.
Source: https://ww2.arb.ca.gov/our-work/programs/truck-and-bus-regulation and https://ww2.arb.ca.gov/our-work/programs/CTC