Transit-free (Tier 1) networks are those that can reach the entire routing table purely through peering, without buying transit from anyone. Anurag Bhatia set out to document which networks held that status at every point since the late 1990s — a gap, because Wikipedia's first documented Tier 1 list only appeared on 14 Nov 2005.

His method combines several sources: an email exchange with Randy Bush, who identified AS701/702/703/704 (UUnet), AS174 (PSI, later Cogent), AS1 (BBN) and AS1239 (Sprint) as transit-free in the early days; the oldest Oregon Route Views dump from 8 Nov 1997; RIPE RIS RRC00 dumps from 1999 onward; and scripted parsing of the Wikipedia Tier 1 page's revision history, cross-validated against public route collectors.

The result is a month-by-month timeline running from before November 1997 to August 2026, tracking how the club evolved. Highlights: AS3561 (C&W America, later Savvis) joined by Nov 1997, AT&T AS7018 and Verio AS2914 around 1998; NTT bought Verio in 2000 for roughly $5.5 billion — a deal that even triggered US congressional hearings over Japanese government ownership of NTT. AS1 lost its transit-free status in 2003 after losing adjacencies. Cogent acquired PSI (and with it the C-root DNS server) in 2002. Level 3 absorbed Global Crossing in 2011, CenturyLink swallowed Qwest, Savvis and eventually Level 3 itself before rebranding as Lumen in 2020, and Cogent took over Sprint's IP network AS1239 in 2023.

The current list (August 2026) counts fourteen networks, including AT&T AS7018, Verizon AS701, NTT AS2914, Lumen/Colt AS3356, Zayo AS6461, Tata AS6453, Arelion AS1299, GTT AS3257, DTAG AS3320, Telecom Italia AS6762, Orange AS5511, Telxius AS12956, Liberty Global AS6830 and PCCW AS3491.

Bhatia is upfront about the method's limits: paid peering deals are invisible in routing data, stale transit relationships can masquerade as peering (he cites Comcast AS7922 still tagged as a customer route by Tata AS6453), and 1990s collector coverage was thin. He also notes that 'having transit' doesn't always mean full reachability — China Telecom AS4809, for instance, buys from Arelion but uses BGP communities to block announcements to peers in Europe, North America and Asia.