Referrer Channel Checker — GA4 Default Channel Test

Key takeaways

GA4 decides the channel from source and medium. UTM parameters override the referrer; with no UTMs, the referrer becomes the source and the medium is organic, referral or (none).
"Unassigned" almost always means a utm_medium GA4 doesn't recognize, like newsletter, post or qr.
Since mid-2026 GA4 has an AI Assistant channel for referrals from ChatGPT, Gemini, Claude, Copilot, DeepSeek and Grok. Perplexity still shows up as Referral, and AI Overviews count as Organic Search.
A lot of real traffic arrives with no referrer at all — email apps, PDFs, messaging, many AI assistants — and is reported as Direct.

How GA4 assigns a default channel

GA4 first works out three values for the session: source, medium and campaign. If the landing URL has UTM parameters, those win. If it has a Google Ads click ID (gclid) and auto-tagging, the source is google and the medium cpc. Otherwise GA4 uses the referrer: a known search engine becomes source google (or bing…) with medium organic, any other site becomes medium referral, and no referrer means (direct) / (none). Then it runs the channel rules in a fixed order and the first one that matches wins:

Order	Channel	Rule (simplified)
1	Direct	Source is (direct) and medium is (none) or (not set)
2	Cross-network	Campaign name contains "cross-network"
3	Paid Shopping	Shopping-site source, or campaign matching "shop"/"shopping", with a paid medium
4	Paid Search	Search-engine source with a paid medium (matches cp, ppc, retargeting or paid…)
5	Paid Social	Social source with a paid medium
6	Paid Video	Video-site source with a paid medium
7	Display	Medium is display, banner, expandable, interstitial or cpm
8	Paid Other	Any other paid medium
9–12	Organic Shopping / Social / Video / Search	Matching source category, or medium social / contains video / is organic
13	AI Assistant	Medium is ai-assistant (set automatically for recognized AI assistants)
14	Referral	Medium is referral, app or link
15–19	Email, Affiliates, Audio, SMS, Mobile Push	Medium (or source) is email, affiliate, audio, sms, or ends with push
—	Unassigned	Nothing matched

Paraphrased from Google's "[GA4] Default channel group" documentation as of October 2026. Google Ads, DV360 and SA360 traffic is classified first using campaign-type data this tool can't see.

How VisitTrack assigns a channel

VisitTrack keeps it simpler and keeps the two questions separate. The channel comes from the referrer alone — AI (chatgpt.com, perplexity.ai, gemini.google.com, claude.ai, copilot.microsoft.com and similar), Search, Social (including link wrappers like t.co and lnkd.in), Referral or Direct. The utm_source, utm_medium and utm_campaign values are stored on the same visit and can be filtered and broken down on their own. So a newsletter click with no referrer shows as Direct in the channel view and as utm_source=newsletter in the campaign view, instead of one value overwriting the other. Note that VisitTrack counts Perplexity as AI, where GA4 currently calls it Referral.

How to use the checker

1.Enter the referrer — what document.referrer would contain on the landing page. Leave it empty to simulate apps, email clients or links opened in a new tab without a referrer.
2.Enter the landing URL, including any UTM parameters or click IDs.
3.Compare the GA4 channel with VisitTrack's, read the rule that matched, and check the notes for common pitfalls.
4.If the result is Unassigned or not what you intended, fix the utm_medium in your UTM builder template and re-check.

Examples

Referrer	Landing URL	GA4 channel	VisitTrack channel
google.com	/pricing	Organic Search	Search
chatgpt.com	/	AI Assistant	AI
perplexity.ai	/	Referral	AI
(none)	/?utm_source=newsletter&utm_medium=email	Email	Direct (campaign: newsletter)
l.facebook.com	/?utm_source=facebook&utm_medium=paid_social	Paid Social	Social
t.co	/blog	Organic Social	Social
(none)	/?utm_source=partner&utm_medium=newsletter-blast	Unassigned	Direct
mail.google.com	/	Referral	Search (google host)

The last row shows a real limitation of host-based classification: a Gmail web click carries mail.google.com as the referrer. GA4's rules treat it as a referral; a simple "contains google." check calls it search. Tag your emails with utm_medium=email and the ambiguity disappears in both tools.

Common channel-attribution mistakes

Custom mediums. newsletter, post, story, qr, banner-ad and similar values put campaigns into Unassigned. Stick to GA4's vocabulary.
Capitalized values in reports. GA4's channel rules ignore case, but source/medium reports still show "Email" and "email" separately.
UTMs on internal links. They overwrite the original source mid-visit in GA4 and start a new attribution touch.
Reading Direct as "typed the URL". Much of Direct is dark social: links from Slack, WhatsApp, native apps, PDFs and some AI assistants that strip the referrer.
Assuming AI traffic is tiny because the AI channel is small. Many assistant clicks arrive with no referrer and land in Direct; AI Overviews clicks land in Organic Search.

Channels are only half the story — the useful question is which channel produces revenue. VisitTrack attributes Stripe, Paddle, Lemon Squeezy, Polar and Razorpay payments to the channel and campaign of the visit, with first-touch attribution across days. Compare it with GA4 on our Google Analytics comparison.

Frequently asked questions

What are GA4's default channel groups?

GA4's default channel group sorts sessions into Direct, Cross-network, Paid Shopping, Paid Search, Paid Social, Paid Video, Display, Paid Other, Organic Shopping, Organic Social, Organic Video, Organic Search, AI Assistant, Referral, Email, Affiliates, Audio, SMS, Mobile Push Notifications and Unassigned, based on source, medium and campaign.

Why is my traffic Unassigned in GA4?

Because no default channel rule matched its source and medium, which usually means a custom utm_medium such as newsletter, post or qr. Changing the medium to a recognized value like email, social, cpc, referral or affiliate fixes it for future traffic; GA4 doesn't reclassify past data.

How does GA4 classify ChatGPT traffic?

Since GA4 added the AI Assistant channel in 2026, referrals it recognizes from ChatGPT, Gemini, Claude, Copilot, DeepSeek and Grok get the medium ai-assistant and land in the AI Assistant channel. Clicks with no referrer still count as Direct, and Perplexity referrals count as Referral as of October 2026.

Do UTM parameters override the referrer?

Yes, in GA4 and most analytics tools that use them for source and medium. If a landing URL has utm_source and utm_medium, those values are used instead of the referrer. VisitTrack stores both: the channel from the referrer and the UTM values alongside it.

Why does so much traffic show as Direct?

Direct means the visit had no referrer and no campaign tags. Besides typed URLs and bookmarks, that includes clicks from many email and messaging apps, PDFs and documents, some AI assistants, and browsers or privacy tools that strip referrers. Tagging links you control with UTMs moves that traffic to the right channel.

Are AI Overviews counted as AI traffic?

No. Clicks from Google's AI Overviews and AI Mode carry a normal google.com referrer, so GA4, VisitTrack and other tools count them as organic search. Google's AI Assistant channel explicitly excludes them.

Referrer channel checker: which channel will this visit land in?