BKK to USA

Hello,

I am flying from Bangkok to Beijing and then off to Los Angeles (USA) in March. I plan on only staying in Beijing 2 days. Does this qualify me for visa-free transit? Also, I read earlier that "Passengers transiting via Beijing Capital International Airport can apply for this free transit permit after arrival." does that mean that I do not have to inform the airline during check in? Or is it safer to do so anyways? Thank you so much for your help in advance.