I (32years old, US citizen) am wrapping up my first 90 days on a non o multiple entry visa (family) on Dec 25.

My wife (Thai) and I just had a second baby. I would like to stay as long as the funds last - hopefully until August, which would be about one year on this visa.

What is the most efficient way of doing extensions/ or border runs to make this visa last?

Can I simply go to the immigration office and will they stamp on another 90 days, and I will do this couple times until the year is up?

Or do I simply do a border run and when I return will they stamp on 90 more days, and I will do this a couple times until the year is up?

Currently, I do not have 400,000 baht in the bank at any one time; I believe this means that the 1 year extension is out of the question. Although, as a side question, does the 400,000 baht have to be in a Thai bank or can the funds be an equivalent in a foreign country?

Thank you

You have to exit the country and re enter to get another 90 days. Do this just before the Visa expires to get another 90 days making a total of 15 months.

The 400,000 Baht has to be in a Thai bank. It has to be there 2 months before applying. Once successful you can start spending it. OR You can use 40,000 Baht a month income if you have that.

It must be in a Thai bank account for 2 months.

If you have a multi entry non immigrant O visa any entry gets a new 90 day stamp. So that can cover you until almost 90 days after it expires (use before 15 March - enter 14 March for new 90 day stay).

You must leave Thailand every 90 days or less. Simple border run - exit Thailand - enter other country - exit other country - enter Thailand.