GA4 Sources report (source / medium)

The Sources report breaks the site's GA4 sessions down by session source / medium, the pair GA4 records for how each session started: google / organic, bing / organic, (direct) / (none), newsletter / email and so on. It is one level finer than Channels, which makes it the place to separate Google from other search engines and to find the individual sites that send you visitors.

What a source / medium row is

GA4's sessionSourceMedium joins two values: sessionSource, "the source that initiated a session", and the session's medium (Data API schema). The source names where the visit came from, such as a search engine, a website or a campaign tag. The medium names the kind of traffic, such as organic, referral, email or cpc.

A (not set) row means GA4 received no source for those sessions. Google's most common explanation is a missing session_start event, for example when the Google tag is not fired on the Initialization trigger (What the value (not set) means).

What the report shows

• Five cards for the segment: Sessions, Active Users, Page Views, Engagement Rate and Key Events, each with its change.
• A bar chart of the ten sources with the most sessions and their share of the total.
• A table with Source / Medium, Sessions, Active Users, Key Events, Engagement and % of Sessions, sorted by sessions and searchable, 50 rows to a page.

Winning and Losing list the sources whose sessions rose or fell against the comparison period. A source that appears for the first time counts as winning.

Checks worth running

• Search engines side by side. Search the table for organic to line up Google, Bing, DuckDuckGo and the rest. If Bing is gaining, the Bing Webmaster Tools reports show what people searched there.
• Referrers that matter. Sort the referral rows by Key Events. A site that sends few visits but many conversions is worth more than its traffic suggests.
• Campaign tags. Search for your own utm_source values. Different spellings of one campaign appear as separate rows, so this is where inconsistent tagging shows up.
• AI assistants. Rows such as chatgpt.com / referral show assistants by name. LLM Traffic groups every known assistant for you.

Turning sources into a segment

Any value in the first column can go into GA4 filters → Custom source / medium: type one or more, separated by commas, and apply. Every GA4 report then counts only those sessions, until you reset the filter. Values must match the text in this column, although case does not matter, and up to 20 are used.

Sources compared with Search Console

google / organic counts the sessions GA4 recorded from Google's organic results, AI Overviews and AI Mode included (Default channel group). Search Console counts clicks on Google results. The two follow each other closely but never match exactly; to compare them page by page, use Blended (GSC + GA4).