Shares of General Motors Co., Ford Motor Co. and Jeep parent Stellantis briefly spiked in after-hours trading Wednesday in the wake of a report that President Donald Trump plans to spare automakers from some tariffs.

Trump is set to exempt car parts from the tariffs that he's slapped on Chinese imports over that country's fentanyl production, as well as from those levied on steel and aluminum products, in what is a "destacking" of duties, the Financial Times report said.

But after initially surging after Trump's announcement, the gains quickly faded; shares of GM $(GM)$ and Stellantis $(STLA)$ ended the after-hours session fractionally higher, while Ford $(F)$ actually fell 0.5%.

The Trump administration has been collecting a 25% tax on every car not assembled in the U.S., and a 25% tax on a range of imported auto parts is due to go into effect "no later than May 3," according to an executive order.

Trump said a week ago that he was "looking at something to help some of the car companies."

If Trump delivers some sort of partial reprieve for automakers, it'll be similar to how he exempted smartphones and other electronics products from recent tariffs a week and a half ago. Trump also made a partial retreat on his "discounted reciprocal tariffs" two weeks ago, and said Tuesday that a tariff level of 145% for China will "come down substantially."