Fleets are tracking two separate regulatory deadlines this month, one federal and one from California, that could each reshape near-term compliance planning for different reasons. The U.S. Environmental Protection Agency’s public comment period on proposed changes to its Model Year 2027 heavy-duty NOx rule closes Saturday, August 29, 2026. The proposal would amend the 2023 rule under Docket ID EPA-HQ-OAR-2026-0728, and EPA held virtual public hearings on the proposal July 29 and July 30. The changes under consideration would not alter the 2027 NOx emissions standard itself. Instead, they would roll back several compliance mechanisms EPA added in 2023. The proposal would rescind the extended emissions warranty, reverting from 10 years and 450,000 miles back to the current 5-year, 100,000-mile structure, and would delay the longer useful-life requirements until Model Year 2030. It would also eliminate the diesel exhaust fluid derate mechanism, which currently forces speed and power reductions when SCR systems are compromised, replacing it with visual and audible dashboard notifications instead. EPA estimates the warranty rollback alone could save up to $6,000 per diesel vehicle if manufacturers pass the savings to buyers. Separately, the California Air Resources Board is working through its own deadline sequence tied to SB 253, the Climate Corporate Data Accountability Act. CARB released Modified Regulations for public comment on July 27, and that comment period closed August 11. The modifications would formally defer the first-year Scope 1 and Scope 2 greenhouse gas emissions reporting deadline from August 10 to November 10, 2026, for companies with more than $1 billion in annual revenue doing business in California. That November 10 date is not yet final. It remains contingent on the outcome of the comment period and subsequent approval by the state’s Office of Administrative Law. CARB also confirmed that Scope 3 emissions reporting will not