The visa grants a stay of 90 days and can be extended twice, totaling 270 days. After quarantine in Bangkok, tourists are free to explore other parts of Thailand as they wish, but the government has indicated that their movements may be monitored by an app or wristband.
The STV program is set to kick in October, initially accommodating one to three chartered flights per week, granting access to a maximum of 1,200 tourists per month.
http://www.thailongstay.co.th/stv_visa.html
https://www.lonelyplanet.com/articles/thailand-special-tourist-visa