What the tag labels
Google's definition of utm_creative_format is "Type of creative, for example: display, native, video, search." It describes the ad rather than the viewer, and it is set by whoever built the link or by the ad platform.
It does a different job from utm_content. utm_content tells two versions of one ad apart, such as two headlines. utm_creative_format sorts ads into broad types. A video ad and a banner ad in one campaign could share every other tag and differ only here.
Google's two answers
Google's UTM help page defines it and then adds: "utm_creative_format isn't currently reported in Google Analytics properties." Google's GA4 dimensions reference, checked on September 27, 2026, lists three dimensions it says are "Populated by utm_creative_format URL parameter": Manual creative format, Session manual creative format and First user manual creative format.
Both pages are Google's. Before you build a report on this tag, open an exploration in your own property, add Session manual creative format, and check whether your tagged visits show a value. If the column stays empty, the note on the UTM page is the one that applies to you.
Not the SA360 or DV360 fields
GA4 also lists creative format dimensions for Search Ads 360, Campaign Manager 360 and Display & Video 360. Those belong to Google's own ad products. The manual creative format dimensions are the ones this tag is meant to feed.
What removing it changes
Nothing for the visitor, and nothing personal is in it. The most a marketer loses is a dimension that one of Google's own pages says is not reported yet. Build tagged links in the UTM builder, and see utm_medium for the older channel tag that GA4 does report.