Solo CK.

Solo CK, at solo.ckpool.org, is run by Con Kolivas, who created the cgminer mining software and the ckpool software the service runs on. He opened it on 31 August 2014. Despite its name, it isn’t a pool in the usual sense: many miners connect to it, but, in his words, “they don’t share the reward.” Nobody signs up; each miner connects with their own Bitcoin address.

So a block found through Solo CK was found by one miner, who gets the reward; sometimes that miner is a group who rented computing power together. The block’s first transaction pays almost all of the reward straight to the miner’s address and a small share to the service, and a miner who never finds a block gets nothing. That reward is separate from the transactions confirmed inside the block. The service, not the miner, chooses which transactions go in: it uses the standard choice of Bitcoin Core, the main Bitcoin software, and leaves none out on purpose.

More than 300 blocks have been found this way, and news of a “solo miner” winning a block is often about one of them. In 2022 Kolivas said about half had come from small miners with one to ten machines at home, and half from groups renting computing power. Some were long shots: he called block 853,742, in July 2024, the first found with a Bitaxe, a pocket-sized mining machine, and said the miner who found block 887,212 with a Bitaxe in March 2025 had less than a one in a million chance of finding a block on any day. Others came from rented power: block 899,826, in June 2025, was “almost certainly a rental”, he said.