Technology History | 鉄鋼ビルディング, Marunouchi — The Tokyo Address That Has Already Changed

Anthropic opened its first office in the Asia-Pacific region on 29 October 2025, and the address it opened at is not the one most directories now give.

The registered home of Anthropic Japan 合同会社 that week was the fourth floor of the 鉄鋼ビルディング (Tekko Building) at 丸の内1-8-2, printed on the company's own Japanese press release.

On 15 June 2026 the commercial register recorded a move to the twenty-seventh floor of the 丸の内ビルディング (Marunouchi Building) at 丸の内2-4-1, several hundred metres west.

The Japanese entity had been assigned its corporation number on 27 May 2025, and 東條英俊 (Hidetoshi Tojo), who came by way of Google Cloud and Microsoft, was named to run it that August.

Dario Amodei flew in for the opening.

He met Prime Minister Takaichi, spoke to the Liberal Democratic Party's digitisation committee, and signed a memorandum of cooperation with Japan's AI Safety Institute covering evaluation methods and the monitoring of new capabilities.

Tojo told reporters that Japan was the first country in Asia the company had entered, ahead of the Bengaluru and Seoul offices it had already announced.

The building deserves a look on its own account.

A Tekko Building has stood on this block since 1951, and the present one was completed on 31 October 2015 — twenty-six storeys, 131.4 metres, offices from the third floor to the twenty-fourth.

Its seismic isolation layer sits between the third and fourth floors, so the office Anthropic opened on the fourth was the first one above the cushion.

The complex is two buildings, a main tower and a south wing given over largely to serviced apartments, and this pin sits on the main tower, where the office floors are.

The tower adjoins the Yaesu north exit of Tokyo Station, the shopping level called TEKKO avenue runs through its basement, and the airport limousine buses pull out from the south wing.

Neither address carries a sign a visitor could photograph; this is a registered office, not a landmark.

Photo: Blue3000, CC BY-SA 4.0, via Wikimedia Commons — 鉄鋼ビルディング本館, 2016.

Sources: Anthropic's Tokyo announcement, 29 October 2025; Anthropic Japan's press release via PR TIMES; the National Tax Agency corporation-number register and gBizINFO; 鉄鋼ビルディング official site; 日経クロステック; ITmedia.