.io

.io is the country-code top-level domain (ccTLD) assigned to the British Indian Ocean Territory, the Chagos Archipelago in the central Indian Ocean. It was delegated by the Internet Assigned Numbers Authority (IANA) on 16 September 1997 and is managed by Internet Computer Bureau Limited, a UK company whose registry services operate under the NIC.IO name^{1 • 2}. Although it codes for a territory with no permanent civilian population, .io has become one of the most widely used domain endings in the technology sector, where the letters are read as "input/output"³.

Delegation and management

The IANA delegation record lists Internet Computer Bureau Limited as ccTLD manager, with an administrative contact in Diego Garcia and a technical contact in Orpington, Kent, in the United Kingdom. The record shows four name servers (a0, a2, b0, and c0.nic.io), registration services at www.nic.io, and a WHOIS server at whois.nic.io; the record was last updated on 18 January 2023¹. The registry's own terms state that "IO Top Level Domain Registry" and "NIC.IO" are trading names of Internet Computer Bureau Limited².

The territory itself has an unusual history. The Chagos Archipelago was uninhabited until the late 18th century, when the French established copra plantations using slave labor in 1793; the islands have been British territory since 1814, when they were ceded with Mauritius. The British Indian Ocean Territory was constituted in 1965 by an Order in Council under the Royal Prerogative⁸. A 2023 academic analysis noted that .io is an Indian Ocean ccTLD whose delegation is held outside the control of the relevant government or former inhabitants, with management and profit sitting with ICB⁹.

The Chagos handover and the retirement question

In October 2024 the governments of the United Kingdom and Mauritius announced a treaty to transfer sovereignty over the British Indian Ocean Territory to Mauritius, raising the question of what happens to a domain that exists only because of that territory's ISO country code^{4 • 10}.

The mechanism is indirect. ICANN relies on the ISO 3166-1 standard to determine which country-code domains are eligible, and an ICANN blog post by Kim Davies, Vice President of IANA Services and President of Public Technical Identifiers, stated that "IO" persisted in the standard with no change as a result of the sovereignty announcement. If "IO" is removed as an assigned code, ICANN's retirement policy applies: a five-year window opens during which usage of the domain must be phased out, and that window may be extended under certain circumstances⁷. An ICANN spokesperson told The Register that multiple outcomes are possible depending on the nature of any ISO change, including maintaining an operational nexus with Mauritius, and noted that the ISO code also serves non-domain uses such as customs, passports, and banking⁴.

Adoption by startups and developers

The extension's popularity with technology companies rests on a reading of the letters as I/O, the input/output abbreviation familiar in software development³. Early devtools, infrastructure startups, and hosting platforms built brands on .io names, and the association held across technology cycles¹¹.

The numbers show the trajectory. Among 1,587 funded Y Combinator startups analyzed in one survey, .io was the leading alternative TLD with 80 companies, a 5.2% share, more than .co and .ai combined¹². Namecheap's analysis of Y Combinator batches found .io at 2% of startup domain share in 2018, rising steadily to 11%⁶. A funding tracker by Atom covering 154 disclosed rounds on .io recorded $9.8 billion in announced capital with a median round of $15 million; among rounds with a resolved vertical, SaaS accounted for 28.5%, AI 17.9%, cybersecurity 15.4%, and fintech 14.6%¹³. The DomainsProject dataset counted 13,234,503 records across 1,592,882 unique base domains¹².

The letters also spawned a game genre. Agar.io drew 192 million visits in 2017, and the .io suffix became a recognizable label for simple browser multiplayer games¹².

Disputes over the domain's governance

The domain's connection to the Chagos Islands' history has drawn formal complaints. On 29 July 2021 the Chagos Refugees Group United Kingdom, supported by the Crypto Currency Resolution Trust of the Bahamas, filed a complaint at the Irish National Contact Point for the OECD Guidelines against Afilias Ltd. and its subsidiaries 101 Domains GRS Limited and Internet Computer Bureau Limited. The complainants, descendants of islanders forcibly deported by Britain, sought restitution and return of .IO, alleging that Afilias acquired the domain knowing its connection to human rights abuses; the United Nations General Assembly, African Union, and International Court of Justice have all found Britain's deportation and continued occupation of the archipelago to be a serious violation of international law⁵. After an OECD human rights ruling, a group of displaced Chagossians announced it would ask ICANN to redelegate the domain¹⁴.

References

1. .io Domain Delegation Data, IANA Root Zone Database
2. NIC.IO Terms and Conditions, Internet Computer Bureau Limited
3. Start-Ups and the .io Domain Trend, Blog Registros.com
4. The .io domain isn't going anywhere in the next few years, The Register (10 October 2024)
5. Chagos Refugees Group United Kingdom, et al. vs. Internet Computer Bureau Limited, OECD Watch
6. Over 50% of new startups don't use .COM domains, Namecheap Blog
7. The Chagos Archipelago and the .io domain, ICANN blog (14 November 2024)
8. History, British Indian Ocean Territory
9. Self-regulation, internet domains and Indian Ocean territories, Journal of Cyber Policy
10. Domain Name News October 2024, Hogan Lovells
11. .io Domain Review: Still the Default for Devtools in 2026, dotappraisals
12. .io: 13.2 Million Domains, Zero Residents, and the Tech Industry's Most Precarious TLD, DomainsProject
13. Startups on .io: funding, verticals and naming, Atom
14. Group to seek .io TLD takeover after OECD human rights ruling, Domain Incite

Topic: Encyclopedia › Technology and the built world › Computing and digital systems › Networks and security › Security governance and internet policy › Internet governance › IP address and critical internet resource governance

Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026

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