It seems like a very smooth and straightforward application process at the embassy in Hanoi and the consulate in Ho Chi Minh City, according to recent feedback.
Hvis du received en 30-day extension on a visa-exempt entry earlier this year, current reports indicate that you will only be granted a 7-day extension on your next visa-exempt entry within the same calendar year.
Get a six months multiple entries tourist visa through the embassy before you leave. With one single border bounce and two local 30 days extensions you can easily stay for six months.
With a US passport, you may enter Thailand on a 60-day visa exemption and apply for a 30-day local extension. You will formally need an onward ticket within the initial 60 days you are stamped in for if the airline requests it at check-in.
Alternatively, if you are over 50, you may apply for a 90-day Non-O visa through the Thai embassy before travelling. This visa is exempt from onward-ticket requirements, and no extension is needed.
In all cases, you will also need to complete the TDAC electronic arrival card within 72 hours prior to arriving in Thailand.
Your plan is generally doable, but there are two important details you need to be aware of regarding extensions. If you enter on visa exempt entries, Thailand now allows only one 30 day extension per calendar year. Any second extension in the same year will normally be limited to 7 days. Since your second stay crosses into 2027, the extension rules will probably reset on 1 January, but only if your second stay is under visa exemption. However, if you instead use tourist visas for both trips, most immigrations still issue 30 day extensions twice. That’s usually a slightly safer option when planning longer stays in the same year. Also keep in mind that everything ultimately depends on your total time spent in Thailand within a rolling period in the discretion of the IO you’re facing not just the calendar year. If your previous stays have not been excessive, you should be fine with the plan you’ve outlined. If your two trips were closer together, a 6-month METV would have been the sensible choice. But with such a long gap between visits and a proper return to your home country in between, both trips should be entirely feasible on either visa exemption entries or single-entry tourist visas provided you have a clean previous entry history.
If you don’t have any recent extensive entry history, you should normally be able to travel without a visa. I recommend limiting your stay to 60 days -that is, using the 60 day visa exempt entry without applying for the 30 day local extension- before travelling to a neighbouring country and staying there a few days before re-entering Thailand. You must be able to show an onward ticket (or a return ticket home) within the 60 days you are stamped in for at each entry into Thailand.
Sorry, I have no specific overview of Mukdahan. You can post a question in the group and see whether any members have more detailed knowledge. I would assume things will gradually normalise, and the visa process in both Vientiane and Savannakhet is generally still reported to work very smoothly.
I don’t have a complete overview, but from what I understand, all of the land border checkpoints were effectively closed for a period, and they weren’t even allowing people with METVs to cross. The most recent updates indicate that Chiang Rai at Chiang Khong and Nong Khai are now allowing travellers with valid visas to pass.