AI Max is enabled on one of my campaigns and I am fairly sure I did not enable it

Both are answerable. When and by whom: Google Ads change history records the setting change with a date and the account it came from, and it will distinguish between someone in your account and a change applied by Google. That's the authoritative record and it's worth screenshotting if the answer turns out to be a rep, because these get applied through auto-apply recommendations more often than people realise. What it changes about your reporting - this is the more consequential half, and your instinct is right. Queries on an AI Max campaign can arrive with no keyword attached. Any report grouped by keyword silently omits those, so your keyword-level view of that campaign has been describing part of it. The search terms are the complete picture; the keyword list isn't. To size it: look at the campaign's search terms and compare the ones with a keyword against the ones without. That tells you how much traffic was outside your keyword list and what it cost. One caution on that exercise. Search term reporting only ever covers the portion of spend Google is willing to show - on a typical account that is roughly half of campaign cost, with the rest below the anonymisation threshold. So calculate the AI Max share against your observable search term cost, not against total campaign cost. Divide by campaign cost and every account on earth looks like a disaster, because you are measuring Google's privacy threshold rather than AI Max. One more thing now that you know it's on: negatives need to sit at campaign level on these campaigns. Ad group level doesn't hold, because the query did not come through an ad group in the first place.