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The Lite Mode has company chats connected to your company data source and a public chat to ask questions that do not need company data sources.
Adding files to a chat
Company chats are configured to answer questions about company data sources. These sources can include documents, emails, SharePoint, Confluence, sites, and more.
You will see an add file icon if the chat was not configured with a data source.
The idea of a chat without data sources is to take advantage of pre-configured instructions. For example, an admin can create a meeting summary chat with all the instructions on how to create the summary, but it will work only after the user uploads the transcript.
You can always use the public chat to ask a question on a file.
You can’t add files to a chat that was defined to give answers on specific data sources.