The change in procedure was announced by CCSA spokesman Taweesilp Visanuyothin, reports the Bangkok Post.
He said the requirement for pre-travel tests would end for all visitors, whether arriving by Test & Go, Sandbox or quarantine channels.
People who enter the country through Test & Go or Sandbox programmes would be given an RT-PCR test on arrival, and be required to perform an antigen self-test on day 5 after arrival, monitored at their hotel.
Sandbox visitors would remain in their reception areas for five days. Visitors in the quarantine scheme, including people caught sneaking in, would be kept in isolation for five days and have an RT-PCR test on day 4 or 5 after arrival.
The CCSA would continue to require visitors to have COVID-19 insurance coverage of at least US$20,000 (B666,175) but was likely to reduce it later, Dr Taweesilp said.
Also, from Apr 1 people would be able to arrive by land through Satun province in the South, in addition to current Nong Khai, Udon Thani and Songkhla.
Arrivals by sea would be allowed through Surat Thani ports, in addition to the present Phuket and Chon Buri.
By air, the reopening would include Hat Yai airport in addition to the current Suvarnabhumi, Don Mueang, Phuket, Krabi, Samui, Chiang Mai and U-tapao airports.
The CCSA hoped to expand the reopening by air to all airports, depending on their readiness, in May, Dr Taweesilp said.