AI Search Study: Sources in Google AI Overviews

This article is the second article in our ongoing research series on AI Search.

Our last post explained how Gemini, the AI model behind AI Overviews (AIO) and AI Mode (AIM), creates fan-out queries. If you missed that one, I highly recommend reading it, as it sets the stage for what we’re diving into now. Fan-outs can heavily impact AIO results.

This time we are zooming in on AI Overviews and its sources.

We wanted to understand what kinds of URLs show up in AI-generated answers and what it means for content visibility in the age of AI Search.

Finding 1: AI Overview spots are limited

The Gemini in AI Overviews is pretty selective. Before you see the usual top 10, you will get a smaller list of selected URLs:

On average, AIO shows 8 sources per response.
Half of the time, it sticks to 7 or fewer.
Only 2.7% of AIOs go over 25 sources.
In some cases, there can be even more than 36 sources!

Finding 2: Top 10 ranking is just a start

Ranking high in the SERP increases your chances of being included in AIO.

However, this does not mean that there is no chance of getting in, even if you are in position 50+. It’s a tiny chance, but hey! Better than nothing.

70% of the sources come from the top 10 organic results. It’s important to note that this applies not only to the original query but also to the related, fan-out queries.

Finding 3: There are two types of sources in AI Overviews

Some sources are more “stable” than others. We call them core sources.

Core Sources: frequently reused URLs that appear across multiple responses for the same query.
Non-Core Sources: appear only once and often don’t come back.

A group of core sources is quite “elite”. On average, only about 9 to 12% URLs re-appear in multiple queries.

Finding 4: Core sources outperform non-core sources

In both tests, core sources are similar and outperform other sources. To put it simply, they rank higher.

Yet another proof that “old-school” SEO remains important for AI results.

Finding 5: Authority and semantics are important

When it comes to domain score, which is Surfer’s internal authority metric on the same lines as domain rating and authority, the difference between core and non-core sources is not so visible.

Authority is important, but it does not constitute a core source.

Core sources have stronger semantic alignment with the query. Both the page titles and the slugs have better semantic alignment with the query.

Finding 6: AIO without sources is a thing!

In less than 1% of cases, AIOs skip sources. When? These are usually super simple or obvious queries, such as definitions or common knowledge, where the model can rely on its built-in knowledge.

Here are the eight categories of queries as classified by Google:

Short facts,
Bool,
Reason,
Instruction,
Comparison,
Definition,
Consequence,
Other (with a lot of Commerce keywords).

How to increase your chances of getting into AI Overview sources?

Here are 3 ways you can get into AIO answers.

Embrace “tradition”

Remember about “traditional” SEO and rank high organically.

Remember about fan-outs

If you didn’t read my previous article on query fan-outs, do it now.

Track core sources

Use core sources to find best places for mentions. Tools like Surfer’s AI Tracker will help you with that.

Securing mentions in related URLs and domains will help both in the short term and long term. The more frequently your brand is mentioned in the dataset, the higher the chance of appearing in LLMs' suggestions.