I don't think they are hiding it, you can see it anywhere even on western internet just by searching.
China could actually further hide it by cooking the gdp adjustment coefficient even more, but they're not doing that, it's past the point where it's worth masking anymore, they can't hide the no1 status anymore than you can hide the average trump voter behind a lamp post. Just like with the lamp post, by trying to do so would only invite additional scrutiny and even ridicule.
So they embraced it for investors, economic partnerships etc but they don't rub it in the face of the west constantly because honestly what point does it serve? As someone else wrote above, when the Qing and British fought, Qing had no1 gdp.
The battlefield is a contest of industry and true prosperity. Gdp only tangentially measures that. US was so threatened by much smaller USSR because USSR invested efficiently in many fields while US didn't. USSR was not cowed if US had shouted they have no1 gdp all day, and neither will US be cowed by China shouting it.
