Google Analytics: Understanding Traffic Sources, How AI Clicks Are Treated, and Why the “Other” Channel Bloats

Google Analytics (GA4) builds every session’s attribution from a few core inputs: referrer headers, campaign parameters, and ad click identifiers. At collection time, it populates traffic-source dimensions such as source and medium, then applies a rule set called the default channel group to bucket sessions into human-readable channels like Organic Search, Paid Search, Organic Social, Referral, Email, and Direct. You cannot edit the built-in rules for the default channel group, but you can create your own custom channel groups for reporting. 

How GA4 Determines Traffic Sources

GA4 identifies a session’s traffic source through a hierarchy of detection methods:

1. GCLID and Google Ads integration: If a user clicks a Google ad with auto-tagging enabled, GA4 decodes the GCLID (Google Click Identifier) to attribute the session to the correct campaign, ad group, and keyword.
2. UTM parameters: If no GCLID is found, GA4 checks for UTM parameters in the landing page URL; specifically utm_source, utm_medium, and utm_campaign. These parameters must be correctly formatted for GA4 to categorize traffic accurately.
3. Referrer or direct detection: If neither a GCLID nor UTM parameters are present, GA4 uses the referring domain or classifies the visit as Direct if no referrer exists.

From these signals, GA4 applies its Default Channel Grouping rules to assign the session to categories such as Organic Search, Paid Search, Direct, Organic Social, Referral, or Display.

Do You Need UTM Parameters for Paid Search?

GA4 does not require UTMs to classify Google Ads clicks as Paid Search when auto-tagging is enabled and the GCLID is preserved end-to-end. GA4 also considers referrers and recognized medium values when applying its channel rules. However, UTMs remain essential for non-Google ad networks and for any scenario where click identifiers are missing or might be stripped by redirects. Consistent UTMs also provide a reliable fallback if auto-tagging fails or parameters are lost. 

A common misconception is that you can force a channel by writing any value into utm_medium. You cannot. GA4 evaluates your source and medium against its rule set, and stronger signals can override your label. For example, mis-labeling a paid-search click with utm_medium=social will not reliably route it to a social channel and is likely to be misclassified as Other or another unintended bucket. The safest approach is to use expected mediums, such as cpc or paid search, for search ads and to keep naming conventions consistent. 

Where Do AI Platforms Appear in GA4

AI assistants and answer engines create new referral patterns:

• ChatGPT and Perplexity: Clicks from web interfaces that pass the referring domain, like ChatGPT or Perplexity, can be classified as Referral. If the app or an embedded browser suppresses referrer data, those clicks can become Direct or fall into Other. 
• Bing Copilot and Google Gemini: When integrated into traditional search results, clicks often appear under Organic Search or Paid Search, depending on whether they originated from a paid ad with valid identifiers. 

Because these sources are emergent and inconsistent with referrers, many teams add custom channel groups to isolate AI-originated traffic, using include rules for known AI referrers and standardized UTM conventions when they control the links they share. 

The Anatomy of the “Other” Channel in GA4

Every marketer has encountered it: that frustrating slice of traffic labeled Other (or Unassigned) in Google Analytics 4. Other is not a traffic source; it is a safety net. GA4 sends sessions to Other when the source and medium do not match any rule in the default channel group. This is why Other tends to swell in modern datasets: privacy features, embedded browsers, and new platforms often remove referrers or alter URLs in ways that break standard classification. 

The Role of utm_medium in GA4 Attribution

While utm_source identifies where the traffic originated (e.g., Google, Facebook, or Mailchimp), utm_medium defines how it arrived (e.g., cpc, email, or social). GA4’s channel rules rely on matching medium values first, then refining attribution with the source. For example:

• Paid Search: medium matches cpc|ppc|paidsearch and source is a recognized search engine.
• Organic Social: medium matches social|social-network|social-media and source matches a known social domain.
• Email: medium matches email.

If you substitute or misspell a medium (e.g., paydsearch or promotedpost), it won’t match these rules and will land in “Other.”

Even if you’ve tagged campaigns, synced your ad accounts, and triple-checked your referral exclusions, GA4 may continue to group a portion of sessions under this ambiguous bucket. To understand why, you need to look at how Google Analytics determines traffic sources, how its channel rules function, and how missteps in tagging or URL handling can push otherwise valuable data into the Other category.

GA4’s Default Channel Grouping depends on strict, rule-based pattern matching between source and medium. When your data doesn’t conform to these patterns, Analytics can’t recognize where the traffic belongs, so it labels it Other or Unassigned. There are several ways this can happen.

1. Misspelled or malformed UTM parameters: Even minor errors, like utm_miduim instead of utm_medium, can break attribution entirely. GA4 only reads exact parameter names, and any deviation means the session lacks a recognizable medium, falling straight into Other.
2. Non-standard medium values: The utm_medium field is critical because GA4 uses it as the foundation for channel grouping. If you use non-standard terms like advert, promo, or bannerpush instead of recognized values like email, social, display, or cpc, GA4 won’t know how to classify the session. For instance, traffic tagged with utm_medium=advert will be treated as Other unless you create a Custom Channel Group that explicitly maps that term.
3. Missing UTM values altogether: If a URL only includes a utm_source but no utm_medium, GA4 has insufficient context to determine the channel. Every session must consist of both for reliable classification.
4. Redirects that strip parameters: Some landing page redirects, especially those on third-party systems or improperly configured servers, can remove UTM parameters before the user reaches the final destination page. The result is an untagged session that GA4 can’t attribute, landing in Other.
5. AI-driven and partner traffic without UTMs: AI marketing platforms, aggregators, or content syndication networks often deliver traffic through APIs or dynamic redirect links. If these lack UTM tagging or don’t pass referrer data, GA4 receives no identifiable source information, again defaulting to Other.

Diagnosing and Fixing “Other” Traffic

The path to cleaning up “Other” starts with identifying which sessions are landing there and why.

• Use the session source/medium report: In GA4’s Reports → Acquisition → Traffic acquisition, switch the primary dimension to Session source/medium. Look for rows where the medium is (not set) or unexpected values appear.
• Verify your UTM tagging: Ensure every campaign link includes: ?utm_source=platform&utm_medium=recognized_medium&utm_campaign=name. Avoid spaces, capitalization inconsistencies, or non-standard values.
• Standardize naming conventions: Adopt consistent, GA4-friendly medium values like:
  • cpc or ppc for paid search
  • paid social or social_paid for paid social
  • display for banners or programmatic ads
  • email for newsletters
  • referral for partner links
• Monitor redirect behavior: Test your links with Chrome DevTools or URL inspection tools to ensure UTMs persist across redirects.
• Create Custom Channel Groups for exceptions: If your business uses specialized channels—like influencer traffic, SMS campaigns, or AI agents—you can define a Custom Channel Group to categorize these mediums properly.

To minimize Other traffic, always use properly structured UTM campaign URLs and validate them before launch. If you’re working with multiple channels, automate your link building with a trusted campaign URL builder to enforce consistency across teams and campaigns. Doing so will ensure your analytics data accurately reflects where your traffic truly comes from—and not in the vague shadows of “Other.”

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