"R-right." It's a rare time when Sans initiates a hug, for sure. Given the stakes... it feels alarmingly like saying goodbye, just in case. And Papyrus shakes a little as he returns it, the metal adding a sharper tone to the slight rattling.

"Later. When things... settle. Or at least when we're not in a science prison, without magic."

Settling might take a while, but he has a lot of talking planned, when the magic situation is resolved. It's only been a couple of weeks, and it's a whole different scale of regret and guilt as what his brother is feeling, but he needs to apologize to Sistina. Even though she'll remember him/them resolving the split, even though she already knows, he needs to say it aloud.

"...Thank you, Sans." Saying things aloud, themselves, is difficult and painful. But maybe sometimes it's more fulfilling.