This is kind of misleading, China and Japan are kind of competing to see who can launch the new generation of 600km/hr maglev trains. Both have test tracks, both have clocked at 600km/hr, both have the actual lines under construction (Shanghai to Beijing, Tokyo to Nagoya).

Neither will likely run at 600km/hr, that's mostly just dick waving.

Construction in Japan has slowed to a crawl and probably won't be done until 2027 at least, and the Chinese CRRC is supposed to start this year but I don't think they have any official service start dates.