Post

SEO 4.0: The Era of Being Indexed by AI Agents Has Arrived

A look at how SEO has evolved from keywords, backlinks, and content quality to the age of AI Agent indexing, and how website content and structure should adapt for the AI era.

Posted
By
8 min read
SEO 4.0: The Era of Being Indexed by AI Agents Has Arrived

Anyone who works on B2C products or operates a public-facing website

is probably familiar with the many ways people try to tune SEO.

As the AI era arrives,

users are no longer only expected to practice search techniques.

They are starting to practice how to refine prompts instead.

It is clear that the rise of AI

will also bring a different kind of shift to SEO.

In the past, SEO was about appearing on the first page of Google search results.

Now, the question is how to make your content discoverable, included, and cited by AI tools.

Content that can be indexed by AI will become more valuable. SEO 4.0 has arrived.

SEO

What Is SEO

SEO stands for Search Engine Optimization.

In simple terms, it is the practice of helping search engines understand your website.

In China, people often use Baidu Webmaster Tools.

Outside China, Google Search Console, formerly known as Google Webmaster Tools, is commonly used to check how a website is being indexed.

For a website to be included by a search engine, it usually needs to go through two processes.

The first is crawling.

Besides Google,

all search engines have their own crawlers.

These crawlers follow links on websites

and download related content.

The second is indexing.

After the crawler downloads a page,

the search engine analyzes and classifies the content,

then stores it in its index.

Some people think SEO is purely a marketing team’s job.

That is only partly true.

Planning how to promote and market content is indeed part of marketing.

But in many cases, SEO performance depends heavily on the health of the website itself.

If a website is slow, hard to use, or thin on content,

its SEO performance is already affected in a meaningful way.

The Evolution of SEO

Although I use terms like SEO 1.0 and SEO 2.0 below, SEO does not actually have standardized phases like Web 1.0 or Web 2.0. People do not usually refer to it this way, and the field is not formally divided by year. More common descriptions are things like the keyword era, the PageRank era, or semantic search, which describe SEO by its dominant behavior or technical characteristics.

SEO 1.0: The Keyword Era (Around 1995-2005)

This was the early stage of almost everything on the web.

Websites and content were still relatively simple.

As long as keyword density was high enough,

pages usually ranked higher.

When we browsed websites as kids,

we sometimes saw pages filled with text unrelated to the actual content.

Sometimes, after accidentally opening the page source,

we would find dense blocks of text that never appeared on the visible page.

Those were products of this era.

At the time, search engines had limited ability to understand content,

so websites relied on large amounts of trendy terms, jargon, filler words, or hidden text to increase their chances of being found.

During this period, Google co-founders Larry Page and Sergey Brin introduced PageRank.

PageRank evaluates the importance of web pages by analyzing the link relationships between them.

When a high-ranking website links to another website,

the linked website may also receive a ranking boost.

This led to link exchanges,

where sites referenced one another to improve rankings.

Influenced by PageRank,

websites began linking to and referencing one another.

Sections like friendly links or recommended sites started appearing.

However, simply linking out to someone else’s website did not help your own ranking very much.

At the same time, web portals were still growing,

so another strategy was to actively submit your website to portal sites.

Once a portal added your URL to its directory,

your site’s ranking could improve further.

The examples above were still relatively legitimate approaches.

But some methods gradually became more distorted.

One example was the rise of blog networks.

People realized that if links were so important,

they could simply build their own sites and link them together.

As a result, large numbers of duplicated blogs and duplicated websites appeared.

Then came content farms.

If your website had good content,

someone could copy it,

making it harder for search engines to identify the original source.

After gaining traffic and ranking benefits,

they might sell the site or fill it with ads to generate revenue.

To fight low-quality content,

Google spent considerable effort adjusting its algorithms.

Social Signals

There was also a period when websites cared a great deal about social visibility.

This roughly crossed the SEO 2.0 to SEO 3.0 period.

But unlike other phases, it did not have a clear defining artifact,

so I place it in the middle rather than calling it SEO 2.5.

The core problem of SEO 2.0 was that backlinks could be bought and manipulated.

At the time, Google began looking for new “trust signals.”

After Facebook became popular worldwide,

many social platforms also appeared one after another,

including Plurk, Twitter, MySpace, tumblr, and others.

People in the SEO community started asking: if many real people are willing to share a piece of content, does that mean the content is high quality?

During that period, some companies even posted on Facebook

and then forced employees to post or share the company article together.

It was, frankly, a rather silly phenomenon.

What did people observe at the time?

Many high-ranking articles had:

  • A large number of Facebook shares
  • A large number of Twitter reposts
  • A lot of social discussion

But correlation is not causation.

In reality, the content probably ranked higher because it was good,

so many people shared it.

After being shared, it was cited and discussed further,

which helped the ranking improve.

It was not that Google raised the ranking simply because everyone shared it aggressively.

SEO 3.0: The Era of Content Quality and Search Intent (Around 2015-2022)

There was a major milestone in 2014:

HTML 5 was finally released.

Before that,

flashy websites were often still filled with Flash.

HTML had relatively few elements available,

and many websites were still built almost entirely with <div>.

After HTML 5 was introduced,

many semantic tags became available,

such as <section>, <article>, <header>, <footer>, <nav>, <aside>, <figure>, and <figcaption>.

These semantic tags helped crawlers and search engines better understand the overall layout of a website.

The arrival of Microdata

also allowed us to add itemscope and itemprop descriptions inside elements such as <p>.

This made it easier for search engines to structure website data

and understand the content of the entire site.

SEO 4.0

Now we are entering the AI era.

Except for the obviously outdated tactics from SEO 1.0,

many of the things mentioned earlier may need to be taken seriously again.

Recently, the World Cup has started again.

On Plurk, there was once a meme where someone said that if Germany won the championship, he would go streaking.

There was also a line about scallions from a crosstalk performance by Feng Yi-gang and Song Shao-qing,

which people on Plurk turned into all kinds of JavaScript effects.

Social signals, which we once considered relatively unimportant,

may become worth paying attention to again.

How SEO Strategy Should Change in the AI Era

For a long time,

when learning about SEO, I was taught to read Google’s Search Engine Optimization (SEO) Starter Guide.

I believe most of what we need to do has not really changed.

At the core, we still need to enrich the content of our websites.

After that, we should use HTML 5 semantic tags properly when building pages,

and combine them with Microdata where appropriate to strengthen the overall structure of the page.

Then, perhaps, we should publish content on Threads

and intentionally or unintentionally spark discussion.

Of course, it is also possible to focus only on that latter part.

But discussion eventually fades.

I believe many fundamentals do not change just because the era changes.

Only by providing high-quality content, improving the overall structure of the website, and making the site easy for users to use

will rankings naturally improve,

and only then will the content naturally be included by AI.

Conclusion

The core of SEO has never been about simply pleasing a single algorithm.

It is about making content understandable, reliably citable, and genuinely useful to users.

From the keyword era to the link authority era, and then to the era of content quality and search intent,

each evolution reminds us of the same thing:

short-term tactics may work for a while,

but in the long run, content quality, structural clarity, and trustworthiness are what matter most.

The rise of AI Agents does not mean SEO is disappearing.

It means the goal of SEO is expanding from “being visible in search results” to “being understood, cited, and recommended by AI.”

So the next steps are actually clearer than before:

keep writing valuable content,

use clear site structure and semantic tags to help machines understand it,

and build credibility through real social discussion.

When a website is useful to people,

it becomes worth indexing for search engines and AI as well.

Further Reading

SEO
SEO AI
This post is licensed under CC BY 4.0 by the author.