Yes. The USA doesn't recognize bitcoin as money, but an asset.

Gift Tax:

* Annual Exclusion: You can gift up to a certain amount of money or assets each year to each individual without incurring gift tax. This amount is called the annual exclusion and is adjusted each year. For 2023, it's $17,000.

I don't think anyone on nostr is sending $17,000 worth of sats in a full year, to one person.

* Lifetime Exemption: If the total value of your gifts in a year exceeds the annual exclusion, it may count towards your lifetime exemption. This is a much larger amount and is also adjusted each year. For 2023, it's $13 million.

Zaps are gifting.