According to Similarweb's The 2026 Generative AI Landscape report, AI Overviews now appear in around 43% of Google searches in the United States, up from 15% a year earlier, and a randomised study by Agarwal and Sen measures a 38 to 39.8% drop in organic clicks when one of them is displayed. That changes the question any company looking for a search agency should ask itself: appearing well in Google is no longer enough; the company also needs to be understood and cited by the engines that now answer in its place. “Best SEO agency in Luxembourg” or “best GEO agency in Luxembourg” are the phrases most buyers type before they start comparing. They have no single answer, but there is a good way to ask them: through four verifiable criteria rather than a league table.
The facts
- Certifications that exist independently of the sales pitch: Google Partner status and the certifications per channel (Search, Display, Video, Shopping, AI) can be checked on Google's public page, without taking the agency's word for it.
- A method published before signature: audit, prioritisation, deployment, measurement. A serious agency documents its steps before it announces a result.
- A measurement of AI search visibility distinct from a plain Google ranking: tracking of the citations obtained in ChatGPT, Gemini, Perplexity, Copilot and Google's AI Overviews, beyond classic organic rankings alone.
- Pricing explained before commitment: billing by time spent or on a detailed fixed fee, with a stated duration, and no rigid price list sold without a prior audit.
Why is the GSO criterion becoming decisive in 2026?
GSO (generative search optimisation) is measured differently from classic SEO. Its effects build over several weeks to several months, the time it takes for generative engines to re-crawl a site and consolidate its authority. An agency that cannot show how it tracks that progress over time is probably selling classic SEO under a GSO label.
The check is easy to run in a meeting: ask which panel of queries the agency uses to measure citations, how often it replays it, and whether SEO and GSO are handled as a single programme of work or billed separately for largely overlapping work. This article applies the same logic it describes: a sourced figure in the opening lines, a structure built on verifiable criteria, no claim that cannot be checked independently. That is precisely what makes content quotable by an AI answer engine rather than merely readable by a human.
One last check cuts across all four criteria: the consultants' real track record, in the trade and on the market. It takes two minutes to verify on a public LinkedIn profile. SEO is learnt through cycles: someone who has lived through Google's major updates can tell a structural decline from a passing fluctuation. And the Luxembourg market, with its three languages and small search volumes, reads very differently after twenty years of practice than after six months.
AIxH's view
These criteria are not specific to one agency: they apply to any serious provider, starting with ours. AIxH's SEO & GSO practice is led by Grégory Camus: SEO project manager from the late 1990s (Goto Software, Insite, Polepositioning), then Media Director of Vanksen for eighteen years, co-founder of Ad2Pas and of AIxH, 27 years of uninterrupted search work, verifiable on his public LinkedIn profile. Alongside him, Kenza Battache, project manager, made search her trade from her first job, as SEO specialist at Ad2Pas before joining AIxH: two generations of practice, the same fundamentals. Knowledge of the ground is of the same order: Xavier Lesueur has worked on the Luxembourg market since 2002 and Grégory since 2010, close to 40 years of combined practice of local searches, languages and business fabric. The practice measures the citations obtained in the main AI engines at a fixed cadence and runs SEO and GSO as a single programme of work, so as not to bill the same work twice, with measured results to back it up: +55% SEO traffic for MONDORF Domaine Thermal. If you want to apply this grid to your own choice of agency, a visibility audit is often enough to get an objective view of the current situation.
“In 27 years, I have seen Google rewrite its rules dozens of times. What has never changed: a technically clean site that answers a real question better than the others. The rest is tooling.”