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Decentralized networks like Ethereum rely on a variety of software to function. To avoid single points-of-failure and achieve fault-tolerance, it is important to have peer-to-peer nodes running different client software.
Despite the importance of client diversity, the majority of nodes on Ethereum's Beacon Chain are using the same client. Not only does this introduce centralization into the network, but it also creates problems for validators and may affect the functionality of a proof-of-stake Ethereum blockchain.