I see no mention of API use on the website, so it’s more of a privacy option for chat. That in itself is useful (no logging, no training on your data, encryption so Proton can’t see or share your data, no ads).
I tried Lumo a while back maybe I should give it a spin again if it's already included in my subscription
Apparently there’s a proxy somewhere on github which munges it into an openai-alike api which you can then feed to those. May give it a shot if i’m bored soon.
the upgrade from older to newer versions of lumo were definitely noticeable