Here's the Tweet by Calle which kicked off the Twitter thread where this was announced:

Yes! We just cracked another nut in @CashuBTC's protocol development: How to handle Lightning's unpredictable fees with no additional rounds of communication?

This was one of the weakest points of the protocol.

Background: https://gist.github.com/callebtc/a6cc0bd2b6f70e081e478147c40fc578

Proof of concept:

https://i.postimg.cc/B6ZtzQsG/image.jpg

https://twitter.com/callebtc/status/1629776855573168129 [Nitter]