21 Inc..

21 Inc. was a US bitcoin company. Balaji Srinivasan, Matthew Pauker and three engineers founded it in secret in 2013 as 21E6, with money from Silicon Valley investors such as Andreessen Horowitz. It began as a mining company. It designed its own mining chips, ran thousands of machines in data centres, cooled in mineral oil, and set out to pay its investors back in mined bitcoin. It raised more than $100 million.

It mined for itself: each 21 Inc. block’s first transaction paid the whole reward to one of the company’s own addresses. That reward is separate from the transactions confirmed inside the block. mempool.space credits it with 1,508 blocks, from 9 April 2015 to 1 March 2016. In August 2015, its busiest month, it found about 4% of all blocks. It had started mining in late 2013, but its earlier blocks aren’t credited to it. That August, as Bitcoin users argued over how big blocks should be, 21 Inc. backed BIP 100, a plan to let miners vote on the limit. Its blocks carried the tag “/BIP100/” from then on.

When bitcoin’s price fell in 2014 and far more mining power joined the network, the company was left with long data-centre leases and falling income, Srinivasan later wrote. He became chief executive in May 2015, and his team got out of all its data-centre contracts, though he didn’t say when. Its last block came on 1 March 2016. 21 turned to other products: the 21 Bitcoin Computer, a small computer with a mining chip, launched in September 2015, and later a service that paid people in cryptocurrency to answer emails. It was renamed Earn.com in 2017, and in April 2018 Coinbase bought it and made Srinivasan its chief technology officer.