Microsoft Excel agents

Copilot in Excel writes real formulas that Excel can undo and check.

Microsoft turned its spreadsheet agent on by default for 30 million paid seats. It could, because every edit lands as an ordinary formula, table or chart that Excel already knows how to undo, recalculate and track.

Image: Microsoft 365 Copilot blog · September 29, 2025

At a glance#

What it does: Builds and edits the open workbook from a chat request: formulas, tables, PivotTables, charts and whole dashboard sheets. Since August 2026 it can also run Python analysis in the workbook.
Who it’s for: Anyone with a Microsoft 365 Copilot license (Business or enterprise), or a Microsoft 365 Premium, Personal or Family plan.
Price: Included in the seat. Microsoft 365 Copilot is $30 per user per month for enterprise and $21 for Business ($18 from July 1 to December 31, 2026), on top of a Microsoft 365 plan. No charge per task.
Model: The person picks Claude (Anthropic) or GPT (OpenAI) for editing. The separate Excel Agent in Copilot Chat, which creates new files, runs only on Anthropic models.
Takes actions?: Yes. Edit mode is the default and changes the workbook directly. Plan mode shows the approach first. Chat-only mode answers without touching cells. A Stop button halts work and Ctrl+Z reverses it.
Claimed results: Microsoft says the agentic Copilot lifted Excel engagement 67%, new-user retention 50% and the thumbs-up rate 65%. It scored 57.2% on SpreadsheetBench in September 2025. Microsoft 365 Copilot passed 30 million paid seats in July 2026.
Launched: Preview September 29, 2025, as Agent Mode. Generally available on the web in December 2025 and on Windows in January 2026. Microsoft dropped the word “mode” in March 2026, and editing became the default in April.

Why it matters#

Microsoft sells Copilot by the seat, $30 a month in enterprise, with no charge per task. So the agent’s job is to make 30 million people open Excel more often and stay. Microsoft’s own numbers say doing the work beats suggesting it: Excel engagement rose 67% once Copilot built the formulas itself. In spring 2026 Microsoft stopped calling this a mode and made editing the default.

Read this page for one idea. Copilot writes ordinary Excel objects, so Excel itself is the safety net. A formula recalculates when inputs change. Ctrl+Z reverses the edit. Co-authors see it. Show Changes logs it. That is what let Microsoft turn the agent on for everyone, and it is also where the gaps are.

How it works#

What happens when a request reaches Microsoft Excel agents.

Ask
A person opens Copilot in Excel, which starts in edit mode, and types “Run a full analysis on this data. Find important insights for making business decisions and create charts.” No range is named and no limit is set.
Plan
Copilot lists its steps in an activity panel: planning workflow steps, exploring workbook structure. In plan mode it would stop here and wait for a yes. In edit mode it keeps going.
Build
It writes into the workbook: a new dashboard sheet, PivotTables, charts and KPI cells. The 2023 sales total is =SUMIFS(SalesData[Sales], SalesData[Year], 2023), linked to the source rows.
Check itself
Microsoft says Copilot evaluates results, fixes issues and repeats until the outcome is verified. In the recording that shows up as a step called “Fixing formula assignment issue”, with a check mark.
Report
The chat summarizes “What I built for you”. Since September 2026 that reply links to each new sheet, table, range and chart, so the person can jump straight to the change.
Keep or undo
Edits sit on Excel’s normal undo stack, so Ctrl+Z reverses them. Show Changes now marks which edits were Copilot’s. Saving makes everything visible to co-authors.

The decisions worth studying#

What they chose, why, and what it costs.

1Editing is the default, and the word “mode” is gone

When Copilot in Excel opens, it is already allowed to change the workbook. Plan mode, which shows the approach first and waits, and chat-only mode are there, but the person has to pick them. Microsoft tried this as “Agent Mode” in a preview program from September 2025. By March 2026 it was saying agent mode had never been a separate mode at all, and in April editing became the default across Word, Excel and PowerPoint.

Microsoft’s reasoning is in its own data. With Copilot doing the work, Excel engagement per user per week rose 67%, new-user retention 50% and the thumbs-up rate 65%. On a seat price, those are the numbers that matter.

The cost: a vague request like “run a full analysis” now edits the workbook directly, with no range named and no plan approved. The activity list ticks each step as done, and the labels say nothing about what was checked. Microsoft’s own benchmark number is 57.2% on SpreadsheetBench, which it published at launch.

Agent mode, Reasoning, and an Activity list with a check mark on each step: Planning workflow steps, Exploring workbook structure, Creating pivot tables and charts, Setting up dashboard layout, Fixing formula assignment issue, Planning the next steps. — Six steps, six check marks. The list says each step ran. It does not say what was tested, or which formula was broken. Microsoft Mechanics recording · October 28, 2025 · 2:17

2Its work is ordinary Excel objects, on Excel’s normal undo

Copilot’s answer is the workbook. It writes formulas, tables, PivotTables and charts into the sheet, with what Microsoft calls editable links to source data. In the Mechanics recording, the 2023 sales total in cell C3 is =SUMIFS(SalesData[Sales], SalesData[Year], 2023). A reviewer can read the calculation, follow it to the source rows, and change a row to see the total move. Edits go through Excel’s own undo stack, so Ctrl+Z reverses them like any other edit.

My read: this is the choice that made default-on safe enough to ship. Microsoft did not have to build a separate approval or rollback system for the agent. Excel already had recalculation, undo, co-authoring and version history, and the agent inherits all of it.

The catch: a typed-in number and a formula result look identical in a cell. Show Changes does not list chart, PivotTable, formatting or filter edits. The check is simple. Change an input and see whether the answer moves.

Cell C3 selected; the formula bar reads =SUMIFS(SalesData[Sales], SalesData[Year], 2023). The Sales & Profit KPIs table lists Total Sales, Total Profit, Units Sold and Avg Margin % for 2024 and 2023 with a YoY Δ column; the pointer partly covers the value in C3. — The 2023 total is a formula over SalesData rows. A reviewer can read it instead of trusting the number, and the 2024 cells beside it need the same look. Microsoft Mechanics recording · October 28, 2025 · 3:27

3Two agents, two model vendors, one spreadsheet

Microsoft ships two Excel agents. Copilot in Excel edits the open workbook, with a choice of Claude from Anthropic or GPT from OpenAI. The Excel Agent inside Microsoft 365 Copilot Chat creates a new workbook behind a read-only preview, saves it to OneDrive, and runs only on Anthropic models. Anthropic became a Microsoft subprocessor for this on January 7, 2026, and Anthropic models are excluded from the EU Data Boundary. An admin who blocks Anthropic removes the Excel Agent for every licensed user.

My read: Microsoft is buying the best model for each job and keeping the price flat. Agent Mode launched on OpenAI reasoning models in September 2025. A model switcher arrived in January 2026. A seat price lets Microsoft swap models underneath without changing what the customer pays.

The cost: a Copilot button in Excel does not prove the Excel Agent is available in your tenant, and two agents mean two answers to where your data goes.

4Reading other files needs a yes, and the yes expires with the chat

Copilot in Excel can pull from the web, from the organization’s files and conversations, and from connectors like HubSpot or Notion. For work files it asks the person to select and confirm which sources it may use. The approval covers only the current chat; a new chat asks again. Microsoft’s doc adds a warning: only approve sources you are comfortable with Copilot pulling into a document you may share.

My read: this is the one place Microsoft put a real gate in front of the agent, and it guards reads. Writes to the open workbook need no confirmation because undo covers them. Reading a private planning file into a shared workbook cannot be undone once the file is saved and co-authors have seen it.

The cost: small friction, and a gap. The gate is per chat, so a long session carries early approvals forward. Once the content is in the sheet, the doc’s only control is the advice to approve carefully.

What to watch#

Default-on meets vague prompts
Edit mode is the default on 30 million seats. A request like “run a full analysis” edits the workbook with no range named. Plan mode exists; someone has to choose it.
Show Changes still has holes
Since September 2026 the Show Changes pane marks Copilot’s edits and the chat reply links to each change. The pane still skips chart, shape, PivotTable, formatting and filter edits, so check charts by hand.
Manual calculation breaks the whole thing
Copilot editing works only with calculation set to Automatic. On a workbook set to Manual, a stale value looks like a broken formula.
Two vendors, one data boundary
Claude and GPT are both on the menu, and the Excel Agent in Copilot Chat is Anthropic only. Anthropic models are excluded from the EU Data Boundary, which matters if your contract depends on it.

What it means for your team#

What to decide before you ship an agent like Microsoft Excel agents.

Product
Default to editing only once your own data shows doing the work beats suggesting it, as Microsoft’s did. Keep plan mode one click away for vague requests, and make each activity step say what it checked.
Platform
Write the agent’s edits as your product’s native objects and put them on the existing undo stack. Then link each line of the agent’s reply to the thing it changed, as Excel has since September 2026.
Security
Ask before the agent reads other files, and let the approval expire with the chat. Know which model vendor handles which feature and which data boundary each one sits inside.
Finance
A seat price means the vendor earns on engagement, so expect the agent to be on by default. Before trusting a Copilot total, change an input and check that the answer moves.

Steal this

Write the agent’s output as your product’s own objects, so existing undo, history and recalculation cover it.
Default to doing the work only when your own data shows it beats suggesting.
Link every line of the agent’s reply to the exact cell, chart or sheet it changed.

Reference#

The evidence behind this teardown: recordings, sessions, what Microsoft Excel agents gets right and wrong, and every source.

Walkthrough · 5 frames

From “Run a full analysis” to a workbook a reviewer can inspect#

Frames from Microsoft Mechanics’ recording of Excel’s Agent Mode, October 28, 2025. A vendor recording, not a live test; Microsoft now documents the in-app experience as Copilot in Excel.

Step 1 of 5: The person asks for a full analysis
Image: Microsoft Mechanics recording · October 28, 2025 · 2:07
1. Agent mode lets Copilot change the workbook itself, not only answer in chat.
2. The person asks for “a full analysis”, insights and charts, naming no range and no limit on what may change.
Step 2 of 5: Copilot reports each step as done
Image: Microsoft Mechanics recording · October 28, 2025 · 2:17
1. Each step in Copilot’s Activity list gets a check mark; the labels don’t say what was tested.
2. Copilot reports “Fixing formula assignment issue”; the frame doesn’t show which formula broke or what changed.
Step 3 of 5: Copilot builds a PivotTable and a summary
Image: Microsoft Mechanics recording · October 28, 2025 · 2:52
1. Copilot leaves a native PivotTable in the workbook: Sum of Profit by segment, with Education at (614,545.63).
2. The chat summary repeats the pivot’s numbers as prose; nothing in the frame checks them against the source rows.
3. Copilot’s summary flags thin evidence: “most rows lack sentiment labels”.
Step 4 of 5: C3 holds a formula, not a typed number
Image: Microsoft Mechanics recording · October 28, 2025 · 3:27
1. The formula bar shows C3’s calculation: =SUMIFS(SalesData[Sales], SalesData[Year], 2023).
2. The 2023 Total Sales traces back to SalesData rows where Year is 2023, so a reviewer can check the source.
3. The frame shows one formula; the 2024 totals beside C3 each need the same check.
Step 5 of 5: PivotChart Fields show what the chart plots
Image: Microsoft Mechanics recording · October 28, 2025 · 3:37
1. The Profit by Segment chart on Copilot’s dashboard is a native PivotChart, selected here.
2. Only two fields are checked: Segment and Profit.
3. Segment sits on the axis and Sum of Profit in Values; the recording doesn’t show a refresh after new data.