Common practice
Advice first, measurement later or never
Work starts with content, schema markup and new pages. Progress is reported as one score from one system. Nobody can tell which change caused which result.
Generative engine optimisation
Generative engine optimisation agency
21x is a generative engine optimisation agency that measures before it builds. GEO, short for generative engine optimisation, is the work aimed at getting your company named in AI answers from ChatGPT, Gemini and Perplexity. 21x measures along the IAB framework and bases the work on a controlled study.
A generative engine optimisation agency works on how often AI systems name your company. 21x measures this in line with the IAB framework, then applies the changes that held up in a controlled study.
+41% visibility from quoting sources · +31% from statistics with a source · -8% from keyword stuffing · Measured in six AI systems
Source: Aggarwal et al., GEO: Generative Engine Optimization, KDD 2024Updated:
Two ways to sell GEO
What a GEO agency should base its work on
Much of what is written about GEO is counted after the fact rather than tested. That makes it easy to sell advice that sounds logical but has no measured effect.
How 21x works
Measurement first, then changes that held up in testing
21x measures where you stand in six systems before changing anything. The work follows what a controlled study found. The same measurement is repeated, so you see what moved.
The difference matters for your budget. Work that is not based on measurement can be carried out well and still change nothing in the answers.
How it works
Generative engine optimisation services, step by step
Five steps, in this order. Each one makes the next worth doing.
Measure the baseline
30 non-branded questions, in English for English-speaking markets and in Dutch for the Dutch market, worded the way your buyers there ask them. Six AI systems, each question asked 3 times, logged out: 540 answers in total.
Check crawler access
If your site blocks GPTBot or ClaudeBot, those systems cannot read anything written afterwards. Access is checked first because it is usually the cheapest fix.
Build presence in the sources answers use
AI answers often name comparison platforms and directories instead of company sites. 21x maps which sources the answers in your market rely on and works on your presence there.
Rewrite key pages with sources and figures
The controlled study found the largest gains from quoting sources and adding statistics with a source. 21x applies this to the pages that matter most in your audit.
Re-measure every month
Same questions, same systems, same counting rules. The comparison shows which changes moved the answers and which did not.
Measured along the IAB framework
The four IAB layers, applied to one company
Example with fictitious data. On 3 August 2026 the IAB published Measuring Visibility in the AI Era, which orders AI visibility metrics into four layers. Each layer builds on the one below it.
Reporting per layer shows where the work should start. A company that never appears needs different work from one that appears but is described as a budget option.
UpciteExample
Question
How visible is a fictitious engineering consultancy across 540 answers?
- Presence: named in the answer28% of attempts
- Prominence: named first9% of attempts
- Portrayal: described accurately, neutral or positive81% of mentions
- Persuasion: recommended outright6% of attempts
Main finding
Present, rarely recommended
The systems know the company but seldom recommend it. The work then shifts from access to the sources that answers rely on.
What it costs
What GEO with 21x costs, phase by phase
Each phase has its own result, and you can stop after any phase. You know the cost of a phase before it starts.
21x
Know where you stand
Basecamp
Insight into 9 areas, 3 to 5 priorities and advice on your next step.
€295one-off
excl. VAT
Wat zit erin?
- Scorecard on 9 GEO areas
- Technical check: schema, robots.txt, sitemap and llms.txt
- 30 questions, each asked 3 times, on 6 AI platforms
- PDF with concrete improvements
- 30 minutes together through the report
- Analysis without implementation
5 to 7 working days
Discuss Basecamp21x
Fix the foundation
Climb
Basecamp plus implementation of the most important improvements to your website.
€695one-off
excl. VAT
Wat zit erin?
- Full Basecamp included (€295)
- Baseline and follow-up measurement after 4 weeks
- Sharpen business profile, content and structure
- Basic structured data and answer blocks
- Check crawler access and sitemap
- Improve internal links on main pages
10 to 14 working days
Discuss Climb21x
Take a bigger step
Summit
A complete improvement round for your most important pages, with an agreed scope.
€1,995one-off
excl. VAT
Wat zit erin?
- Analysis and implementation included
- Improve business profile and key pages
- Answers to 10 important customer questions
- Technology, AI access and speed
- Before and after measurement: 30 to 50 questions, each asked 3 times
- Weekly update and a 30 minute call
- Delivery advice and plan for what comes next
3 to 6 weeks
Discuss Summit21x
Keep climbing
Altitude
Digital PR, monthly measurements and upkeep of the information about your business.
€695/ month
excl. VAT
Wat zit erin?
- Baseline and monthly measurement on 6 AI platforms
- Research into the sources AI uses
- Profiles, pitches, press releases and listings
- Quarterly comparison with competitors
- Maintain schema, llms.txt, business facts and crawler access
- Monthly report with work and next steps
- Upcite account included (not charged separately)
Minimum 3 months
Then cancel monthly
Work completed in one phase remains yours, whether or not you continue.
What held up in testing
Three results from the controlled study behind GEO
Researchers from Princeton, Georgia Tech, IIT Delhi and the Allen Institute for AI changed one thing at a time on real pages. They measured the effect across ten thousand queries.
+41%
visibility when quotations from credible sources were added to the text
Bron: Aggarwal et al., GEO: Generative Engine Optimization, KDD 2024
+31%
visibility when concrete statistics with a source were added
Bron: Aggarwal et al., GEO: Generative Engine Optimization, KDD 2024
-8%
visibility after keyword stuffing, worse than making no change at all
Bron: Aggarwal et al., GEO: Generative Engine Optimization, KDD 2024
Note what this study measures: how visible a source becomes once it has been retrieved. It does not make a system retrieve your page in the first place. That is why 21x works on access and outside sources before it rewrites pages.
Questions
Questions about GEO agencies
What does a GEO agency do that an SEO agency does not?
An SEO agency works on positions in a list of search results. A GEO agency works on whether AI systems name your company in their answers, and how. The foundation overlaps, but the measurement differs: per system, repeated, and without a fixed position.
Is a generative engine optimization agency the same as a GEO agency?
Yes. Optimization is the American spelling and optimisation the British one. The research paper that introduced the term in 2023 uses the American spelling.
Does the IAB framework tell you how to optimise?
No. The IAB framework covers measurement only and leaves optimisation methods out of scope. The changes 21x makes come from the controlled study by Aggarwal et al., published at KDD 2024.
Which AI systems does 21x measure?
ChatGPT, Claude, Gemini, Perplexity, Google AI Overviews and Microsoft Copilot. Each system is reported separately, because they differ in how often they name companies at all. One combined score would hide that difference.
How long before AI systems name my company?
That depends on your market, your current presence and how often the systems refresh their sources. 21x gives no fixed term. The monthly re-measurement shows whether, and where, the answers change.
What do generative engine optimisation services cost?
That depends on what the baseline audit finds, the size of your site and the competition in your market. You know the cost of each phase before it starts. The packages on this page show what each phase covers.
Can a GEO agency guarantee mentions in ChatGPT?
No. Answers vary each time a question is asked, and no agency controls them. Google states that nobody can guarantee a first position in its search results, and the same caution applies here.
Next step
Measure before you spend on GEO
Stan Vreuls, Founder of 21x
A call is enough to judge whether an audit makes sense for your company. If the answer is no, you will hear that too.
stan@21x.nl