Do I still need the Claude Excel add-in, or can Claude AI (desktop/co-work) write directly into an Excel file the same way?

The view expressed was that you likely don't need the Excel add-in anymore. If you're using the desktop version of Claude with the co-work feature, Claude can go into files on your computer and edit them directly, effectively acting like a human using your computer, including writing into an Excel file — so the dedicated plugin isn't required for that. Choosing between the two comes down to preference: if you want to visually stay working inside Excel, the Claude plugin for Excel makes sense since you remain in the spreadsheet. If you don't care about staying in Excel, Claude co-work can do the work in the background without you ever seeing the Excel file open. One caveat raised: the co-work feature is only available on the desktop app, not on the phone app or claude.ai website, so work done that way isn't accessible on the go the same way chat-based work is. Co-work was also described as useful more broadly — e.g., it can organize source documents across many client folders, as long as the firm is comfortable with Claude having access to view those documents' contents. For smaller volumes where full file access isn't wanted, some people instead take a screenshot/snip of just the non-sensitive portion of a document and paste that into a chat, though that approach doesn't scale well for high volume.