Fernando Alonso will have exclusive use of Honda's updated engine at the United States Grand Prix, with Jenson Button sticking to the old specification for now.
The new Specification 4 engine, believed to deliver around a 20bhp boost in power, was tested by Alonso during Friday practice at the Russian Grand Prix.
With McLaren encouraged by early feedback, and Honda's post-race analysis confirming it was happy with the updates, it has given the green light to it being raced by Alonso in Austin.
However, with a long lead time to manufacture new specification parts, Button will have to wait a little longer to get his hands on the engine.
Once Honda has built the new engine, then Button is expected to race it – even though it will mean a grid penalty.
For now Button will stick to the Specification 3 power unit that was introduced at the Italian Grand Prix.