First user campaign dimension
The first user campaign dimension records the campaign name attached to a user's very first session and keeps it fixed for the user's lifetime. GA4 derives it from utm_campaign (or auto-tagged Google Ads campaign) on the first visit. Being user-scoped, it answers 'which campaign first acquired this person?' and will not match the session campaign of any later visit — a distinction that matters for cohort attribution.
What this means
First user campaign is the campaign GA4 attributes to a user's first session — typically the utm_campaign value present on that first visit, or the campaign from auto-tagged Google Ads. It is locked at acquisition and never changes.
That fixed, user-level scope makes it the dimension for judging a campaign's lasting effect: not just the sessions it generated, but the lifetime behaviour of the people it first reached.
Why it differs from session campaign
Session campaign is re-derived each visit; first-user campaign never is. A user first acquired by a 'spring-launch' campaign who later returns via 'newsletter' shows first-user campaign = spring-launch and session campaign = newsletter. Both are correct at their scope; equating them mis-attributes acquisition credit.
- User-scoped: fixed at the first session
- Derived from utm_campaign or auto-tagged campaign
- Differs from per-session session campaign
How it appears in analytics and logs
A first-user campaign value is the campaign that first acquired the user. It will differ from session campaign for returning users, which is expected at this scope.
Diagnostic use case
Use first-user campaign to measure the long-run value of an acquisition campaign — retention and repeat behaviour of the users it first brought in.
What WebmasterID can help detect
WebmasterID can hold a user's first-touch campaign separately from per-session campaign, so acquisition-campaign cohorts do not blur with later visits.
Common mistakes
- Treating first-user campaign as a per-session metric.
- Expecting it to update when the user returns.
- Confusing it with session campaign in the same report.
Privacy and accuracy notes
First-user campaign derives from the first visit's campaign tags, not from cross-site identity. WebmasterID attributes first-touch campaigns first-party.
Related pages
- Campaign dimension
The campaign dimension labels a visit with the marketing campaign that drove it. It is populated from the utm_campaign parameter on a tagged link, or auto-tagged by an ad platform's own click ID. Any visit without a campaign tag — most organic, direct, and untagged referral traffic — shows '(not set)', which is the absence of a campaign rather than a campaign named '(not set)'.
- Session campaign dimension
The session campaign dimension attributes an entire session to a single campaign, fixed when the session begins. GA4 derives it from utm_campaign or the auto-tagged Google Ads campaign present at session start. It is session-scoped, so it answers 'which campaign drove this visit?' — different from event-scoped campaign (which can change within a session) and from first-user campaign (the lifetime acquisition campaign). Mixing the three is a common attribution error.
- First user medium dimension
The first user medium dimension records the medium of a user's very first session — organic, cpc, referral, email, (none) for direct — and keeps it fixed for the user's lifetime. GA4 derives it from utm_medium or the inferred channel on the first visit. It is user-scoped, so it answers 'through what kind of channel did we first acquire this person?' rather than how a later visit arrived, and confusing it with session medium distorts cohort attribution.
- Attribution analytics
First-touch campaign credit vs per-session campaign.
Sources and verification notes
- Google — [GA4] User and traffic acquisition dimensions
- Google — [GA4] Custom campaigns (UTM parameters)
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.