I could potentially make a separate API that will return URL instantly, and will redirect to Tenor while upload is prepared, and then serve local copy. If you are interested, let me know.
There have been a couple comments in my feed from people expecting to paste a nostr.build address so that could be cool Your API is fast already, it's mostly that nip98 AUTH requires me to publish a Kind 27235 note, which takes time to broadcast with my current library Were you thinking this API would be separate from nip98?
Nip98 does not require anything, just a signed header. You are talking about nip94, that can be pushed async.