Here is a similar question in metaculus. Notice that metaculus forecasters give a 60% probability that China's GDP will surpass US GDP by 2050.

Also take a look at the numeric market for when China's GDP will surpass that of the US:

china keeps kneecapping its own industries (video games, afterschool tutoring, electric scooters). if they just deregulated and stopped trying to do communism they’d beat the US for sure.

As it stands, it all depends on whether Xi will be able to make good top down decisions. maybe their big solar play will work out idk

What happens in 2050 if it looks like China is unlikely to pass the US?

@JoshuaWilkes Would still resolve "after 2049". I appended "or never" to make that more clear.

You got me thinking about some cases like "China doesn't exist anymore" or "US doesn't exist anymore". However, sometimes states disappear only temporarily.