Flights are available at this price starting in late February with daily returns valid through April 10, 2019. With all airlines offering the same amount you'll have a nice selection of departure times and connections to choose from. Air Canada is offering some lower prices at $396 roundtrip; however, those will require a long layover and sometimes jump up in price on the final booking screen.
Logan (BOS) isn't the only airport that is seeing these excellent deals to China, many other cities have airfares well below the average price on these routes so make sure to check out our Shanghai (PVG) and Beijing (PEK) deal pages to see what's available from your hometown airport.
As an example, on United I found seats departing BOS on Wednesday, March 13 and returning from PEK on Saturday, March 23, 2019. Other dates are wide open during the mentioned travel window.
Need a place to stay in China? Here's what we found for the sample dates via Hotelwatchdog.