Tick the AI engines you want to count. You get the exact regex to paste into a GA4 Session source filter, plus the clicks to get there.
Pick an engine and I will build your filter.
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1. Which engines do you want to count?
2. Your Session source filter
Tick at least one engine and the regex shows up here.
Gemini trap. The hostname is gemini.google.com, so any check that asks whether the source contains google claims it first and files those sessions under organic search. Match your AI hosts before you match Google, and this regex does that for you.
DuckDuckGo is mixed. That hostname carries ordinary search traffic as well as AI answers, so treat the number as an upper bound rather than a clean AI count.
Perplexity is why you are doing this by source. Google's native ai-assistant channel does not include it, so a channel-based report leaves it out.
3. Where to paste it
In GA4, open Reports, then Acquisition, then Traffic acquisition.