Here is a numeric market:

How does it resolve if china surpass us gdp before 2030, but us got back at 2030?

@MarisaKirisame Notice that the close time is 2040, so it will resolve at 2040. The title means that if China surpasses US GDP in 2030s, it will also count.

@quther I see, I had misunderstood the question.

Related:

Looking at the historical data of the GDP of both countries from 1960 till date, it can be inferred that the the Chinese GDP has always lingered behind the US GDP 62 times in a row. Even though the Chinese GDP has witnessed a considerable change in the annual growth rate, performing a linear regression on both data shows that by 2030, the USA GDP will be at $25.79 Trn. while the Chinese GDP will be trailing at $ 16.41Trn .

@felixokwaraoha I agree with Felix

That’s according to Bloomberg Economics, which now forecasts it will take until the mid-2040s for China’s gross domestic product to exceed that of the US — and even then, it will happen by “only a small margin” before “falling back behind.” Before the pandemic, they expected China to take and hold pole position as early as the start of next decade. https://www.bloomberg.com/news/articles/2023-09-05/china-slowdown-means-it-may-never-overtake-us-economy-be-says#xj4y7vzkg

This trend is likely to continue, with forecasts indicating that the US GDP will reach $25.79 trillion by 2030, while China's GDP would be $16.41 trillion. These figures, obtained from linear regression models, highlight the US economy's strength and durability. Despite China's rapid economic growth and development, the US economy's size and diversity, together with its inventive capacity and large role in global banking and trade, give it a distinct advantage. While China has achieved significant economic development, the GDP disparity between the two countries underscores the United States continued worldwide economic dominance. This long-term lead illustrates the United States' ability to adapt and grow in the face of a variety of global difficulties. https://www.bea.gov/

https://statisticstimes.com/economy/united-states-vs-china-economy.php

https://www.imf.org/en/Publications/WEO

http://www.stats.gov.cn/english/

I assume this is at market exchange rates, not purchasing power parity?

Unlikely the way the CCP is focusing on control vs economic growth. They've already killed more than 1 100+ billion dollar industry if it doesn't fit with their goals.