What Is Referral Traffic? How GA4 Counts It, When It Is Spam, and Where AI Fits

Referral traffic is visits that come from someone clicking a link on another website. A blog post links to you, a reader clicks, and GA4 records the visit as a referral from that blog.

Search engines, social networks, email, and ads each get their own channel. Referral covers what is left: plain links on other sites and apps. It is often small. It can also be some of your best traffic, because the visitor arrived with context.

What referral traffic means in GA4

In GA4, referral traffic is any session whose medium is “referral”, “app”, or “link”. Google describes it as visits from non-ad links on other sites and apps, such as blogs and news sites.

When a visitor clicks a link, the browser usually passes along the referrer. That is the address of the page they came from. GA4 reads it and records the session as, for example, example-news.com / referral.

The same click can land in different channels depending on where the link sat:

For the full list of channels and how GA4 picks one, see our guide to website traffic sources.

Where to find referral traffic in GA4

1. Open Reports, then Acquisition, then Traffic acquisition.
2. Find the Referral row to see total sessions, engagement, and key events.
3. Change the dimension to Session source / medium. Each row ending in ”/ referral” is one site that sent you visitors.
4. Add a second dimension, Landing page + query string, to see which of your pages they linked to.
5. To see the exact page that linked to you, build an Exploration with the Page referrer dimension.

Sort by key events, not by sessions. A site that sent 40 visits and 5 sign-ups matters more than one that sent 400 visits and none. To confirm that a new partner link sends visits at all, follow the checks in how to check website traffic in GA4.

When referral traffic is spam

Referral spam is fake traffic that puts a domain in your referral report so you will visit it. The spammer is after your click.

The signs are easy to spot:

• You have never heard of the domain.
• Sessions last close to zero seconds and view one page.
• The visits come from countries or devices that do not fit your audience.

GA4 removes traffic from known bots on its own, using Google’s research and the IAB bot list. It cannot catch everything, and it does not show you what it removed. Do not open the spam domain. Build a report filter or an Exploration segment that leaves it out, and block it at your host or CDN if it keeps coming. Our guide to bot traffic in GA4 covers the full cleanup.

Self-referrals and payment pages

GA4 does not count your own domain or its subdomains as a referral. If a related domain shows up, it is usually a separate checkout, a payment processor, or a login page. Customers leave for it and come back, and GA4 sees the return as a new referral.

The fix is in Admin, then Data streams, then Configure tag settings, then List unwanted referrals. Add the domain there. Google allows up to 50 entries per data stream.

How AI assistants show up as referral traffic

AI assistants now send visits too, and they show up in three different ways.

ChatGPT tags its links. OpenAI’s publisher FAQ says ChatGPT adds utm_source=chatgpt.com to the links it sends. Seer Interactive found that citation links carry the tag most often, but not every link does.

GA4 now has an AI Assistant channel. Search Engine Journal reported it in May 2026. Before that, these visits mostly landed in Referral. GA4 matches the referrer against a list of assistants. Google names ChatGPT, Gemini, DeepSeek, Copilot, and Grok as examples. Clicks from Google’s own AI Overviews and AI Mode stay in Organic Search.

Some assistants still look like plain referrals. Perplexity is not on Google’s named list. Seer’s tests showed Perplexity visits as perplexity.ai / referral. Check your own reports to see where each one lands.

Apps built on OpenAI’s API use a different tag

On October 9, 2026, we sent 11 questions to OpenAI’s gpt-5.4-mini model through its API, with web search turned on. Its answers linked to 24 different web pages. Every one of those links ended in utm_source=openai, not chatgpt.com.

So a visit from a third-party app built on OpenAI’s API may show up as source “openai”. To catch all of it, search your Session source list for “chatgpt”, “openai”, “perplexity”, “gemini”, and “copilot”.

Some AI clicks arrive with no referrer at all and fall into Direct. We explain why in what direct traffic is. If you want AI tools to cite you in the first place, start with our guide to LLM SEO.

Is referral traffic paid or unpaid?

Referral is an unpaid channel in GA4. A paid placement belongs somewhere else. Tag sponsored posts and newsletter ads with a paid medium such as cpc or paid, and affiliate links with affiliate. GA4 then files them under a paid channel or Affiliates, and your Referral report stays a clean record of links you earned.

How to grow good referral traffic

1. Publish something worth linking to. Original data, a free tool, or the clearest answer to a common question earns links on its own. Dated numbers give other writers something to quote.
2. Get listed where your buyers look. Industry directories, partner pages, and “tools we use” pages can send steady visits.
3. Write for other sites. Guest posts, expert quotes for reporters, and podcast show notes all carry links.
4. Fix links that point to dead pages. Old URLs that return a 404 error waste every click. Find them with the methods in how to find all pages on a website, then redirect each one to its closest live page.
5. Judge each source by what visitors do. Compare engagement rate and key events per session. A referrer that sends few visits who buy is worth more than one that sends many who leave.