So I received my O-A visa few weeks ago. If I were to enter (first time with this visa) sometime in December, would immigration officer at the airport ask me for evidence of insurance ? or is this still a gray unknown area.
TLDR : Answer Summary
When entering Thailand with an O-A visa, it is confirmed that you will need to present valid health insurance that meets the specified requirements upon arrival. The allowed stay on your visa will correspond with the duration of your insurance, up to a maximum of one year. This requirement is clearly outlined in the Immigration rules.