If you are travelling through Singapore on a single ticket, then you could be considered to be in transit and not required / expected to step outside the airside cordon.

If yes, do recheck the US testing requirement - it should count from the first flight you take on the trip, regardless of transit (though stopovers break that, I believe). [EDIT]As shared out by quant88 below, the CDC requirement is ‘first flight’ OR flight to USA if overnight stop, no mention of stopover.

According to SQ’s site, transit can be up to 48hrs, but confirm directly with the airline per your circumstances.

There are two transit hotels airside if you prefer not to wait in the concourse / lounge - they must be pre-booked.

If you are not on a single ticket, then currently you are required to go through immigration. If that occurs, then all of you need to a. immediately head to and self isolate at a hotel or other residential property, b. only leave to do your test at the testing center or clinic and return to self-isolation, and c. remain isolated until your test results come through (hoping they’re all negative). The ‘Transit Singapore’ thread in this forum has more discussions on that.

For now, if I had a trip through SG and transiting: if no good reason to stopover, I would stay airside, even if the transit hotels are by the hour and cost extra, especially with all the uncertainties.