What Is a .si Domain? Slovenia’s Extension, Explained
Two letters, open to anyone in the world, and since the White House renamed AI to "Super Intelligence" in September 2026, the fastest growing extension on the internet. What .si is, who runs it, what it costs, and what the rush means for you.
October 4, 20268 min readTLDs · .si · Super Intelligence
The short answer. .si is the country code extension of Slovenia. It is run by Register.si, part of the Academic and Research Network of Slovenia (ARNES), and anyone anywhere can register one: there is no residency or company requirement. Names can be as short as two characters and cost about $12 to $20 a year. Outside Slovenia it now reads as SI: in September 2026 the US government started calling AI "Super Intelligence", and .si registrations rose more than twentyfold in a month.
Who runs .si
Every country code extension has a registry that keeps the list of names. For .si that is Register.si, operated by ARNES, the Academic and Research Network of Slovenia. You do not buy from the registry directly: you register through one of its accredited registrars, the same way you would buy a .com.
The registry publishes registration data through RDAP, the modern replacement for WHOIS, at rdap.register.si. That matters more than it sounds: it is what lets a checker like Axath tell you, from the registry itself, whether a .si name is taken.
Who can register a .si domain
Anyone. The .si rules are open to natural and legal persons without geographical restriction, so a company in the United States or a founder in Singapore can hold a .si name just like a Slovenian business.
What the rules do ask is the usual good faith: the name must be registered for lawful purposes, must not infringe anyone's rights, and must not break the law, public order or morals. That is standard for country code extensions and mostly matters if you are thinking of registering someone else's brand.
The rules and the price
| Rule | .si |
|---|---|
| Minimum length | 2 characters |
| Who can register | Anyone, worldwide |
| Local presence | Not required |
| Allocation | First come, first served |
| Registry fee | €10 a year, flat, no premium tier |
| Registry | Register.si (ARNES) |
| Availability data | RDAP at rdap.register.si |
The two-character minimum is the interesting one. Many extensions reserve or price short names separately. In .si, short names follow the same rules as long ones.
So does the price. Register.si charges registrars €10 a year for every name, and it did not change that during the rush: there is no premium tier and no surcharge for short or popular words. What you pay on top is the registrar's margin. At the time of writing, Dynadot asks $12.05 for the first year and $13.51 to renew, and Porkbun $20.42 and $17.53. GoDaddy, the largest registrar, did not sell .si yet in early October. The .si extension page has the current prices side by side.
Why .si is suddenly valuable
For years .si was simply Slovenia's domain. Then "SI" started to replace "AI".
The industry moved first. The companies building the most advanced models stopped describing their goal as artificial intelligence and started calling it superintelligence. Ilya Sutskever, a co-founder of OpenAI, named his company Safe Superintelligence. Meta reorganised its AI work as Meta Superintelligence Labs. In May 2026 the startup Recursive Superintelligence came out of stealth with $650 million in funding and bought recursive.si for $20,000.
Then the US government made it official. On 22 September 2026 President Trump told the UN General Assembly that US documents would switch to "the much more accurate term super, as opposed to artificial". A week later, on 29 September, he signed Executive Order 14434, "Inaugurating the Era of Super Intelligence". It tells federal agencies to use "Super Intelligence" and "SI" instead of "artificial intelligence" and "AI" in official correspondence, public communications, websites and policy documents, and gives the White House science adviser 60 days to propose a legal definition of SI.
That is exactly the shift that made .ai valuable in 2023: when a two-letter abbreviation becomes the name of a technology, the matching two-letter extension becomes the obvious address for companies working on it. .si is that extension for SI.
It also reads as a word. "Sí" means yes in Spanish, "sì" in Italian. A name like say.si reads as a sentence, the trick that made .ly and .io names memorable.
The September 2026 rush in numbers
Demand was already rising before the speech: the registry counted 186,337 .si names in June 2026, with 6,342 added that month. Then:
- 25 hours after the UN speech, daily .si registrations overtook .ai for the first time.
- 46,066 .si names were registered in September, a 2,199% increase according to the registry.
- 11,000 were registered on 30 September alone, the day after the order was signed.
- 241,459 .si names existed on 1 October, 13,603 of them registered in the previous 24 hours.
Hostinger says .si became its second most popular extension, after .com. Aftermarket prices followed: otherwise.si sold for $18,888 on 24 September.
Who is buying, and what that means for you
Most of the rush is investors, not products.
- About 52% of the .si names registered at Dynadot between 19 and 22 September were listed for resale straight away.
- At Hostinger, only around 3% of new .si names explicitly relate to AI; over half of its .si buyers came from the United States and India.
- More than 44,000 .si names, about a fifth of the extension, match an existing .ai name letter for letter.
Two things follow. First, the obvious AI words went in the first days, and many of them are now on sale for far more than the €10 registry fee. Before you pay an aftermarket price, check that the name is not simply free, and that a different short word would not do. Second, nobody knows yet whether "SI" will stick. The order only changes the vocabulary of the US federal government: it is not a law, it does not rewrite existing statutes or contracts, and everyday speech may keep saying AI. Even the boom is modest for Slovenia: the extra September revenue is put at around €300,000, against roughly $85 million that .ai earned Anguilla in 2025.
Security researchers have not seen a rise in .si phishing so far, but they did find 87 .com names pairing famous brands with "superintelligence", each listed for $20,000, registered the day the order was signed. If you own a brand, it is worth checking whether your name is being held in .si.
Is .si right for you
A .si name makes sense when:
- your brand reads well with "si" at the end, or the two letters work as part of the name;
- you are building in AI and want a short alternative to an expensive .ai;
- you can also hold the .com or redirect from it, so people who type .com still find you.
It is a weaker choice when your audience will assume it is a typo, when you need the trust of a long-established extension for payments or email, or when the only names left are aftermarket listings priced on the hype.
For a direct comparison, read .si vs .ai: Is .si the Next .ai?. To register one, follow How to Register a .si Domain.
Check a .si name
You can check any .si name, or a list of hundreds, in the Axath checker. Results come from the registry's own RDAP data and show the current price at several registrars, so you can see straight away what is free and what it will cost. To see whether your brand is already held in .si or elsewhere, run it through Brand Check.
Find your .si name.
Check a list of names in .si and the extensions next to it in one go, with live registry results and registrar prices.
Check .si names