How extensive is China 's program to give grants to U.S. startups to get them to relocate to China to gain access to their technology?

As @Joseph Wang mentioned, this is lots of paperwork and dealing with Chinese administration. It will help you get access to people in local administration, which is a non negligible factor while doing business in China.

Mostly, these kind of grants seems to be targeted towards Chinese people that have started tech companies in the US and are willing to move part or all of their activities back to China. I know of a similar case in France (blockchain uni research spinoff). Most support for grant allocation went through the Chinese Academy of Sciences because one team leader was previously a researcher there.

This text was originally published in quora.