Thanks for that bobbytables
We've already got 20hrs of flying and transits from Australia before we get to SGN, a 4 hour saving is a godsend.

Is international to international transit possible through SGN nowadays? I’m looking at SFO-SGN-SIN and wondering what I need to transfer in HCMC, will I need to enter Vietnam? Will I need a visa?

It is possible, but it's quite a hassle compared to most other airports in the region. I did it a few times before the pandemic, and I was always checked for a Vietnamese visa at my origin airport even though by the rules I didn't need one, strictly speaking. This isn't a problem for me since I have a 5-year visa, but if you don't want to argue with the check-in staff, you can just get a visa on arrival approval letter from a travel agency for a couple of bucks. On arrival, there is a transfer desk before immigration which isn't always staffed, and you may have to chase someone down to issue your onward boarding pass and re-check your tests, documents and other materials before reentering the international terminal. I'd certainly prefer most other SE Asian airports for a transit unless you've got something very specific in mind.

Just follow the transit/transfer signs and should be fine. I have done it a few times and had no issues.

Added: Vietnam may not be allowing transits right now.

Looks like no medical declarations re required. Does that mean no more PC-Covid?

Back in Vietnam after a trip overseas. No PC-COVID declarations needed for the international or domestic flight. Negative test result is now checked only on check-in, no checks on arrival in Vietnam.

Flurry of articles in local media today about removing the testing requirement, so expect that to happen soon.

That is the best news.
We re flying in to HCM on the 1st July and are hoping the testing requirements are dropped. The wife was 1 week away from arriving to VN when the borders closed and then she lost her mum to covid in July last year. Of we miss this trip due to a positive test she will be devastated.
Here's hoping it's lifted as soon as possible.

And it appears from 00:00 hours on 15/5 the pre departure covid test has been scrapped by the Vietnamese government.
fantastic news.

Great news! But too late for me. I am on my way to Hanoi and had to arrange for one. Now, let’s get rid of the medical insurance!

Great to hear this. Just need Indonesia to do the same for my trip to SE Asia in June/July.

Nobody asked me about my insurance, but I'm not on a tourist visa, so that may be why. But I've also heard from several recent tourist arrivals and none of them were asked either. Would be interested to know if you were.

Hey bobbytables,
What's the situation like with domestic travel out of SGN at the moment?
Have you experienced long check in lines or long waits with security?
We've just bought tickets to CXR but only have a 2hr transit coming in on SQ.
Just slightly worried if the check in lines are ridiculous.

It's generally pretty efficient. Really large queues only tend to happen around national holidays, the rest of the time they are pretty good at having enough staff working for the passenger load. 2 hrs should be OK if the inbound is on time. If you can, check in online / with the app, so that you can just drop bags.

If you feel like it's getting tight when you get to security, show your boarding pass to one of the myriad staff standing around, and they might let you skip the queue. I've only had to do it twice, both times around lunar new year when queues can be huge, but it worked both times.

Finally, you can consider upgrading to business class SGN - CXR, if the price is reasonable, which would give you access to the priority check in queue and priority security lanes, and free/cheap rebooking in the event that your SQ flight is delayed and you miss the connection. I don't think it's strictly necessary, with 2 hours between flights, but it would reduce the risk.

Thanks for the help.
We did almost book business, might look into changing it.

Nearly open fully!