Do I need to transfer 800k THB internationally for a new non-O retirement visa in Thailand?

It depends on the immigration office some you do and some you don’t

for the application to the "change of visa type" from a touristic entry to a 90-days Non-Imm-O retirement visa on Immigration inside Thailand, you need an already existing Thai bank account with a minimum of 800,000 THB in it on the day you apply. No seasoning required at this point. However you must prove the money came from abroad

*** Immigration Pattaya (Jomtien) does NOT follow this police order but come up with their own – different! – rules

*** for an application to a 1-year extension of the stay permit out of a 90-days stay permit you received when you entered Thailand on a 90-days single-entry Non-Imm-O retirement visa, you need to prove with a bank letter that a minimum of 800,000 THB has been on your Thai bank account for a minimum of 2 months. For this application it is irrelevant where the money came from

funds of 800k baht in your thai bank account to meet the financial requirement for in-country initial non-o visa based on being over 50 must be transferred internationally.

no specific period of seasoning is required for initial visa application at the immigration office. funds in your thai bank account for minimum two months is only for a one-year extention. <- these are what in the police order.

but jomtien and a few other offices require you to have funds for certain amount of time (2 or 3 month) even for initial via appicatipn.

Check with your local office for their requirements