Default Channel Grouping

Default channel grouping is the fixed set of rules Google Analytics 4 uses to sort every session into a traffic channel such as Organic Search, Paid Social, or Email. GA4 reads the source, medium, and campaign values on each visit and matches them against Google’s published definitions. The rules cannot be edited, which is why the channel a visit lands in depends entirely on how the link was tagged.

Universal Analytics called it “Default Channel Grouping”. GA4 calls the dimension Session default channel group, with a user-scoped twin, First user default channel group.

Why Default Channel Grouping Matters

Channel grouping is what makes reporting comparable. Without it, every campaign, referrer, and ad platform would sit on its own row, with no way to weigh email against paid social at a glance.

It also decides where budget conversations start. The Traffic acquisition report opens on Session default channel group, so this grouping is the first number most stakeholders see. If a paid campaign is tagged with utm_medium=paidsocial, GA4 files it under Paid Social. Tag it utm_medium=fb-ads and it drops out of the paid channels entirely.

The 19 GA4 Default Channel Groups

GA4 ships with 19 named channels, plus Unassigned as the fallback. Google lists them alphabetically:

• Affiliates: medium is affiliate
• AI Assistant: traffic from recognized AI assistants, medium ai-assistant
• Audio: medium is exactly audio
• Cross-network: campaign name contains cross-network, which covers Performance Max and Demand Gen
• Direct: source is (direct) and medium is (none) or (not set)
• Display: medium is display, banner, expandable, interstitial, or cpm
• Email: source or medium is email, e-mail, e_mail, or e mail
• Mobile Push Notifications: medium ends in push or contains mobile or notification
• Organic Search: source is a known search engine, or medium is exactly organic
• Organic Shopping: source is a known shopping site, or the campaign name matches a shopping pattern
• Organic Social: source is a known social network, or medium is a social value such as social or social-media
• Organic Video: source is a known video site, or medium contains video
• Paid Other: a paid medium that does not match Search, Social, Shopping, or Video
• Paid Search: a known search source plus a paid medium
• Paid Shopping: a known shopping source or shopping campaign name, plus a paid medium
• Paid Social: a known social source plus a paid medium
• Paid Video: a known video source plus a paid medium
• Referral: medium is referral, app, or link
• SMS: source or medium is exactly sms

AI Assistant is the newest addition. Google added it to Default Channel Group reports on May 13, 2026, classifying referred visits from tools like ChatGPT, Gemini, and Claude. It works off the referrer header only, so an AI answer that sends a visitor with no referrer still lands in Direct. The change is not retroactive.

How GA4 Assigns Channels

GA4 evaluates each session against the channel definitions and assigns the first rule that matches. Three inputs drive nearly every decision: source, medium, and campaign name.

Medium does the heaviest lifting. Most rules test medium alone, and the paid channels all require a medium that reads as paid before source is even considered. Setting utm_medium to a value Google recognizes is the single highest-leverage tagging decision for channel reporting.

Source narrows the paid and organic splits. GA4 checks the source value against internal lists of known search engines, social networks, shopping sites, and video sites. A source of facebook with a paid medium becomes Paid Social. The same source with no medium becomes Organic Social.

Auto-tagged Google Ads traffic skips the UTM path. When a gclid is present and the accounts are linked, GA4 uses the ad network and campaign type reported by Google Ads instead, which is how Performance Max campaigns land in Cross-network.

Default Channel Group vs Custom Channel Group

The default channel group is read-only. To change how traffic is bucketed, create a custom channel group in Admin > Data display > Channel groups, which requires Editor access at the property level.

Custom channel groups use the same building blocks, with rules written against source, medium, campaign name, and campaign ID. Common uses: splitting Email into newsletter and lifecycle, or grouping influencer traffic that otherwise scatters across Referral and Organic Social.

The limits are strict:

• Standard properties: 2 custom channel groups
• Analytics 360 properties: 5 custom channel groups
• Up to 50 channels inside any one group

Custom channel groups apply retroactively. Historical sessions get re-sorted under the new rules, so a group built today can re-read last quarter.

Why Traffic Lands in Unassigned

Unassigned means no channel rule matched. It is a tagging problem, not a GA4 bug.

The usual cause is an invented medium value. utm_medium=newsletter, utm_medium=partner, or utm_medium=qr are all reasonable to a marketer and meaningless to the rule set, so those sessions have a source and a campaign but no channel. Missing medium values and casing that breaks a source match produce the same result.

Treat a rising Unassigned row as a naming audit rather than a reporting question. The fix for unassigned traffic in GA4 starts with listing every distinct medium value in the property and mapping each one to the channel it was supposed to reach.

Frequently Asked Questions

What is default channel grouping?

Default channel grouping is the built-in rule set GA4 uses to classify each session into a channel such as Organic Search, Paid Social, Referral, or Direct. It reads the source, medium, and campaign values attached to the visit and matches them against definitions Google publishes and maintains. The rules cannot be edited, and they apply as data is collected.

How many channel groups does GA4 have?

GA4 defines 19 default channels, plus Unassigned for sessions that match nothing. The list includes paid and organic versions of Search, Social, Shopping, and Video, plus Email, Referral, SMS, Audio, and AI Assistant. Google adds channels over time, most recently AI Assistant in May 2026.

Can you change the default channel grouping in GA4?

No. The default channel group is fixed and cannot be edited. Create a custom channel group instead, under Admin > Data display > Channel groups. Standard properties allow 2 custom groups and 360 properties allow 5, with up to 50 channels in each.

Do custom channel groups apply to old data?

Yes. Custom channel groups apply retroactively, so historical sessions are re-sorted under the new rules once the group is saved. This is the main practical difference from the default channel group, which is assigned at collection time and never revisited.

What is the difference between a channel group and a source/medium?

Source and medium are the raw values on the visit, such as google / cpc. A channel group is the bucket those values roll into, such as Paid Search. One channel contains many source/medium pairs, which is what makes channel reporting readable at the top of a report.

Check how a tagged URL will be classified before the campaign goes live with the free GA4 URL tester at linkutm.