Do I need to prove 3 months of seasoning for my Non-O Retirement extension in Thailand?

Yes, you need to provide proof of having maintained the required funds for three months after your Non-O Retirement extension is issued. This is typically checked during your next extension application where you'll need to supply 12 months of bank statements to verify that you maintained at least 800,000 THB in your account for three consecutive months, without dropping below 400,000 THB. Additionally, proof of income showing a minimum of 65,000 THB can be acceptable as well.