What are the requirements for obtaining a non-immigrant O visa in Thailand for retirement purposes?

Mine was easy, went while in USA had a retirement OA visa, came opened bank account, now maintain 800k in that account. Multiple annual extensions

Sadly, as you are an American passport holder, you cannot use the monthly income method for the first year.

Methods to meet the financial proof for an initial Non-O based on retirement for 90 days and/or following a 1-year extension based on retirement are:

A. monthly income of more than 65k baht, with a letter of guarantee from your Embassy in Thailand

B. 800k baht in a Thai bank account

C. combination of A and B total 800K baht

The monthly international transfers method is only acceptable for the second or later year's extension.

Unfortunately, the US embassy in Thailand no longer issues an income affidavit.

So if you want to apply for a visa and 1-year extension, you need to have:

1. 800k baht in your Thai bank account for in-country visa,

2. then 800K baht in your Thai bank account for 2 calendar months when you apply for a one-year extension

3. then keep 800K baht for 3 months after an extension is granted, and keep 400K baht for the rest of the year.

You have to check the local immigration first if they accept "partially banked money + international transfers for 12 times" for a 1-year extension.

If they do, you can start monthly transfers as soon as you get an account, then use those for the second 1-year extension and after.

It could be problematic if you apply for the first 1-year extension at a different office from the one you apply for an initial in-country Non-O visa. Plan accordingly.