In the latest update from the TAT, it was announced that the sandbox scheme is being expanded and simplified effective from November 1st 2021.
Arrivals from any of the listed 63 countries world-wide may now visit any of the 17 “Blue Zone” areas without the need to do hotel quarantine (Air travel only). Incoming travelers must have been staying in one of the listed countries for no less than 21 days before travelling to Thailand. however returning Thais and foreign residents who previously left Thailand are exempt from this requirement.
New arrivals are still required to spend the first 7 days of their stay in Thailand in one of the Blue Zone Sandbox areas before moving to other destinations in Thailand.