Ethereum is far and away the most decentralized ledger. Its real node count is 10,000 to 20,000

Ethereum's validator count, about 869,000 today, is sometimes presented as a count of the machines running the network, but that framing is inaccurate.

Each validator is a staked identity with its own keys, and it runs as software on a node. A single node can run thousands of them.

A node is a computer running Ethereum's client software. It checks every new block against the protocol's rules on its own.

Since the Merge, a full Ethereum node runs two clients side by side: an execution client, which runs transactions and keeps track of balances and contracts, and a consensus client, which follows the beacon chain and agrees with the rest of the network on which blocks are final. Each one talks on its own peer-to-peer network, so the public trackers count them separately.

On Oct 5, Etherscan found 11,781 execution nodes (Etherscan), and ProbeLab found 8,397 consensus nodes (ProbeLab).

Every one of these counts misses nodes. These tools find nodes by reaching out to them, so any node behind a home router that won't take incoming connections never gets counted.

Researchers at IMDEA Networks, who checked 36 blockchains every day for seven months, say their own Ethereum count is only a minimum for this reason. They also found thousands of extra nodes they couldn't tie to any one network (IMDEA study), and they found that Ethernodes counts far fewer Ethereum nodes than their own tools found.

ProbeLab, the team behind the consensus count above, watched network traffic on another chain, Celestia, instead of reaching out to nodes. It found about 20% more nodes than reaching out did, and it says Ethereum likely has hidden nodes too.

My estimate is that Ethereum's real node count is 10,000 to 20,000.

Even at that smaller number, Ethereum is far and away the most decentralized ledger in the world. Its nodes run six separately built execution clients and six consensus clients, so a bug in one of them doesn't affect every node. Ordinary people can run one of those nodes at home. The ethereum.org site links a guide that shows you can turn even a Raspberry Pi 4 into a full Ethereum node.