At least five automakers are expected to endorse a dramatic boost in fuel efficiency requirements to 54.5 mpg by 2025. The five companies include GM, Ford, Chrysler, Honda, and Hyundai (which also includes the Kia brand).

The agreement between these major automakers and the White House came after the Obama administration slightly softened its proposal to boost fuel efficiency standards to 54.5 mpg — down from 56.2 mpg — by 2025.

The new plan calls for hiking fuel efficiency for light trucks 3.5 percent annually from 2017-21 — and then 5 percent from 2022-25. It would hike car fuel efficiency 5 percent annually over the period. It also carves out special rules for “work trucks” — heavier light-duty vehicles used primarily for construction jobs. After the various credits are included, the actual fleet-wide average actually could be less than 50 mpg by 2025.

The National Highway Transportation Safety Administration said last fall that hiking fuel efficiency 5 percent annually would boost the cost of an average vehicle by at least $2,100.

The White House, California and automakers have been in discussions for weeks to try to extend national standards, which would avoid a patchwork of national and local rules.

“This is not easy, but the companies are being very cooperative,” Transportation Secretary Ray LaHood said in an interview. “These deliberations are going on somewhere between 12 and 18 hours every day for the last several days … I think we will get there.”