The initial announcement stated international companies could be used wef September, although it didn’t come from Dept of Immigration but some other govt source, and as we know the left hand is frequently contradicted by the right hand…so much also depends on the attitude of the specific immigration office itself - Phuket, for example, has never shown any interest in wanting to see insurance for an OA EoS.
Logic would dictate any EoS prior to September would require the 400 000/40 00 baht local policy, and any EoS after that date would require 3.5m baht, local or otherwise. As with most LoS matters, however, it’s like a pig on acid - you don’t know which way it’s going to go….