Anyone else think the nuclear announcement is a concession that Xi requested?

The timing is... suspicious.

China is the nuclear laggard of the three apocalyptopowers. It wants to catch up, and has the technical and industrial means to do so, but it probably needs to test its new tech. However, it's invested a lot in portraying itself as good guy to America's putative evil empire.

The US' negotiating position vis China is objectively bad, but people can find creative… sweeteners.