Slovenia's two letters, read a new way
.si is the country-code top-level domain for Slovenia, the small Alpine country between Italy, Austria, Hungary and Croatia. The registry is run by Arnes, the Academic and Research Network of Slovenia, under the name Register.si — a public institution, which makes .si one of the steadier ccTLDs to build on.
The domain picked up a second meaning as artificial intelligence did. Once .ai became the default ending for AI startups, the industry's next big word was superintelligence: Safe Superintelligence Inc. launched in 2024, and Meta set up Meta Superintelligence Labs in 2025. Founders looking for an ending that says "SI" the way .ai says "AI" landed on Slovenia's code.
Open to everyone
Unlike some country codes, .si doesn't ask for a local address. Register.si's general terms let any natural or legal person hold a .si name, registered through an accredited registrar for one to five years at a time. The zone is DNSSEC-signed, and registration data is available over both WHOIS and RDAP.
.si or .ai?
If you're naming an AI product, .ai is still the ending people recognize instantly. .si is the sharper, rarer signal — it suggests you're aiming past today's AI, and good short names are easier to find than on .ai. Many teams will want both: see our .si vs .ai comparison.
Good for
- AI labs, agents and research projects built around "superintelligence" (SI)
- Short brands that missed out on the .ai land rush
- Slovenian businesses, and Spanish or Italian wordplay ("sí" means yes)
Watch out for
- Outside the AI crowd, .si still reads as Slovenia, not "superintelligence"
- Popular short names are being picked up fast as the term spreads
- Pair it with your .com or .ai so email and word of mouth don't go astray
.si by the numbers
.si is the internet country code for Slovenia. It's one of Central Europe's ccTLDs, the two-letter domains reserved for countries and territories.
Outside Slovenia, plenty of people know .si for a different reason: it reads as superintelligence — the AI-era ending after .ai. That second meaning doesn't change who's in charge, though. The domain still belongs to Slovenia, and its registry sets the rules.
A little context on Slovenia: the capital is Ljubljana, the main language is Slovene, the currency is the Euro (EUR) and the international dialing code is +386.
Next door on the map, you'll find .at for Austria, .hr for Croatia, .it for Italy and .hu for Hungary.
IANA lists Academic and Research Network of Slovenia (ARNES) as the manager of .si, with an address in Slovenia. The registry's website is https://www.registry.si. ccTLD managers set their own policies — who can register, which second-level names exist, pricing to registrars — so those rules differ from country to country.
Under the hood, the root zone points to 6 name servers for .si, every one of them reachable over IPv6. The delegation is DNSSEC-signed, so resolvers can verify that answers for .si haven't been tampered with on the way. Registration data is published over RDAP and WHOIS (the WHOIS server is whois.register.si).
.si vs other endings
.si FAQ
What does .si stand for?
Officially, Slovenia — "SI" is its ISO 3166-1 code. In the AI world, .si has also become shorthand for "superintelligence", the way .ai stands for artificial intelligence.
Is .si a good domain for an AI company?
It can be. It's short, it carries the "superintelligence" meaning for an AI audience, and it's open to registrants anywhere. For a mass-market brand, also hold a .com or .ai so people who guess the ending still find you.
Who can register a .si domain?
Any natural or legal person, worldwide. Register.si's general terms define a holder simply as "a natural or legal person" and don't require an address in Slovenia.
How long can I register a .si domain for?
From one to five years at a time, and you can renew.
Who runs the .si registry?
Arnes, the Academic and Research Network of Slovenia — a public institution — operates the registry as Register.si.
What country is .si?
.si is the country-code top-level domain for Slovenia, in Central Europe. Online it's also used for superintelligence — the AI-era ending after .ai.
What does .si mean in an email address?
Only that the sender's domain is registered under .si. Because .si is also used for superintelligence, it doesn't necessarily mean the person is in Slovenia.
Is .si DNSSEC-signed?
Yes. The root zone has a DS record for .si, so DNSSEC validation works all the way down from the root.
How do I look up who owns a .si domain?
Query the registry's registration data service: the WHOIS server is whois.register.si, and RDAP lookups go to https://rdap.register.si/. Many registrants use privacy services, so personal details may be hidden.
Sources
Data from IANA root zone version 2026102000. Last changed October 21, 2026. Spotted something wrong? Tell us.
