Sami Pienimäki said in the video inside the Greetings from Kaupinoja hackday blog post, that Jolla is aiming 5.3 to get into CBeta in October. I don’t know if @0312birdzhang is in CBeta, or if it is possible to set your release version to 5.3 with ssu at this point, but let’s hope all the supported devices gets official 5.3 release before end of the year.