Lumo is an AI chat assistant developed by Proton, the Switzerland-based company behind services including Proton Mail and Proton VPN. It is designed to answer questions, help with writing, summarise content, explain concepts, and support other productivity tasks. Proton says Lumo does not use conversations to train its AI models, does not keep chat logs, and stores conversations using zero-access encryption so that Proton cannot read them. Lumo is available through the web and mobile applications, with free and paid access options.