Marathon owns the most bitcoin, currently holding 8,956 BTC. Half of their bitcoin is self-mined, but they also bought 4,813 BTC in January 2021. While some other miners aim to be vertically integrated and own their own data centers, Marathon only invests in ASICs and bitcoin.
Core Scientific is the second-largest bitcoin hodler of the miners, with 7,355 BTC. We find Hut 8 with 6,115 BTC in third place and Riot in fourth place with 5,783 BTC.