Do you need to refrigerate tahini sauce after opening?

If you're using store-bought...
Easy answer,
YES
... Unless you live in Siberia

As long as there is a layer of oil on top covering the paste it is ok to store at room temp - until it smells rancid. I used some to make gomae the other night and was at least a year old.

I would refrigerate. Sesame can go rancid pretty fast.

This question comes up frequently, and FOOD52'ers seem to be pretty evenly divided. You'll know if it's gone off, as it will smell rancid.

I've always refrigerated it.

We always have refrigerated ours, with no issues either!

I never have, with no issues.