I asked Lumo:

> Is Lumo open source?

>> I'm not sure if Lumo is open source. Let me check the official information about Lumo to confirm this.

>> Based on the information provided in the Lumo FAQ, Lumo is not open source. The models powering Lumo are open-source large language models (LLMs) that have been optimized by Proton, but Lumo itself is a proprietary product developed by Proton.

I think this is a bit of an accidentally correct confabulation - I can't find that in any Lumo faq - but it seems consistent with Proton overall; afaik they don't open source any server side/service code?