What changed
The COPILOT function let a cell send a prompt plus a range to Copilot, for example =COPILOT("Classify sentiment", B2:B100). It only ever shipped as a preview, through the Frontier and Microsoft 365 Insider programs. Microsoft's support page now states that from 14 September 2026 the function is no longer available in Excel.
Will this break your workbook?
Only if someone used the preview. Work through this list:
- Any cell showing #NAME? where a text summary or label used to be - most likely a COPILOT cell that has recalculated.
- Cells still showing old results. These are cached values. They look fine until something forces a recalculation, then they turn into #NAME?.
- Downstream formulas. A COUNTIF, pivot or chart reading those cells breaks the moment the source cells do.
- Shared copies. Each colleague's copy recalculates on its own, so one file can be intact while another is broken.
How to fix it in three steps
First, find every COPILOT cell: Ctrl+F → Options → Within Workbook, Look in Formulas, search COPILOT( and press Find All. Second, select the results and paste them as values, before anyone presses F9 or Ctrl+Alt+F9. Third, decide which results need to stay live. A one-off summary can stay as pasted values. A monthly classification is better rebuilt as an ordinary formula or a Power Query step, which gives you the same answer every time it refreshes.
The lesson for preview features
A preview function can be withdrawn, and when it goes, every cell that uses it becomes an error. Keep previews out of reporting workbooks that other people rely on, or paste their results as values on the day you use them.
