Hello,
That is nothing new, we already discussed about that here - Mbed Studio IDE/Online 1.4 - Mbed Studio - Arm Mbed OS support forum
Announcement of open beta release is here but I not found more informations. I also don’t understand that it was not published officially on the Mbed.com website.
ARM Keil Studio Cloud already replace Mbed Studio Online what was in closed beta last year - Arm Keil | Cloud-Based Development Tools for IoT, ML and Embedded
BR, Jan