Track Changes Isn't a Diff: What Word's Markup Misses in 2026
Track Changes feels like proof of what changed. It is actually a log of what got recorded, and those two things only match when tracking was on, never interrupted, and nothing was done outside it.
Track Changes is the first thing most people reach for when two people edit one document, and in 2026 it is also how AI editors show their work. Claude for Word's suggested-edits mode writes every change as a native Word tracked revision, and Microsoft has been bringing the same behaviour to Copilot. That makes the red-and-green markup feel like proof. But Track Changes is a record of what the software was told to log, not a comparison of two documents, and the gap between those two things is exactly where unnoticed changes live.
Have two versions and no markup? ClearDiff compares them side by side in your browser, with nothing uploaded anywhere.
What Track Changes Actually Records
According to Microsoft's documentation, Track Changes marks insertions, deletions and formatting changes, with each author shown in a different color. It is a running log, and it only runs while tracking is on. Any editor can switch it off unless the author locked it with a password through Lock Tracking, and when it is off Word simply stops marking changes. The marks already in the file stay until someone accepts or rejects them, which is also why a file can look tidy while hiding what happened before the last "Accept All."
| Situation | Track Changes | Diff of two versions |
|---|---|---|
| Tracking was off during an edit | Change is not marked | Change is found |
| Someone clicked Accept All, then kept editing | Earlier history gone, later edits only if tracking was on again | Finds every difference from the version you hold |
| Counterparty returns a "clean" copy | Nothing to read | Shows each difference from what you sent |
| Who made a change, and when | Author name and timestamp | Not shown: it reports what, not who |
The last row matters as much as the others. Track Changes is not the weaker tool; it answers a different question. It tells you who did what and lets you accept or reject each edit individually. It cannot tell you whether the log is complete.
What Changed in 2026
Software reviewers wrote about this shift in April 2026. One review of Claude for Word, dated April 11, described the suggested-edits mode this way: "every change Claude makes shows up as a native Word tracked revision." A separate guide to redlining in Word called AI-assisted redlining "table stakes" and noted that both Claude for Word and Microsoft Copilot produce native tracked changes. Reports from the same month described Copilot's Track Changes support as still in preview, on Windows only.
That is good for reviewability: each AI edit can be accepted or rejected on its own. It also moves the trust question. When the markup looks authoritative, the natural habit is to read the markup and skip the rest. The same review warns that prompt injection, where hidden instructions inside a document steer the AI into unintended actions, is a real risk when reviewing counterparty drafts. In that case you want a check that does not depend on how the edits were produced.
Track Changes answers "what did the editors, or their tools, tell me they changed?" A diff answers "what is actually different between these two files?" Those sound like the same question until the day they give different answers.
The Leak Runs the Other Way Too
Markup that is left in a file creates its own risk. UK tax authority HMRC's internal guidance lists tracked changes, comments, hidden text and editors' names as metadata that can be disclosed to the wrong people when a file is shared. Canada's Office of the Privacy Commissioner makes a related point: edits that were never accepted stay embedded in the file, so a recipient may be able to read decisions you thought were removed. Accepting or rejecting everything before sending is the standard advice, and a comparison of the final text against the version you meant to send is a cheap way to confirm that you did it correctly.
A Workable Habit
- Keep tracking on while people collaborate. The author and timestamp record is useful and a diff can't recreate it.
- Compare end states before sign-off. Diff the version you approved against the version you received back, whether it came with markup or not.
- Diff before you send, too. Compare the cleaned file against your intended final to confirm that nothing was left in or out.
For contracts in particular, see Why Contract Reviews Require Version Comparison, which covers the cost of a single unnoticed change in more detail.
The honest summary: Track Changes is a log, a diff is a comparison, and you need both. The log tells you who proposed what and lets you decide edit by edit. The comparison tells you whether the document in front of you matches the one you think it does. AI editors now write their work as tracked changes, which makes the log better but does not make it complete, so it is still worth checking the two end states against each other before anything is signed or sent.
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