Imagine opening your Bitcoin wallet and sending a payment.
You control the keys. The coins are yours. The transaction is valid, and you have attached a competitive fee.
Then you wait.
Another block appears. Your payment is still unconfirmed. Another follows. Still nothing.
There are plenty of ordinary explanations for that experience. But consider a different possibility: the services coordinating much of Bitcoin’s mining have decided they do not want your transaction in their blocks.
Your private keys remain secure. Bitcoin’s supply rules remain intact. Nobody has hacked your wallet.
Your problem is getting someone to confirm the payment.
Self-custody gives you control over signing a transaction. Getting it settled requires a willing miner.
That distinction deserves more attention, especially when you look at how Bitcoin’s blocks are produced.
** CryptoKeyhole’s reading through October 28, 2026** puts the five-largest-pool share at
The measurement matters. Each day’s largest pools are ranked afresh; this is not necessarily the same fixed set of five throughout the month. It measures attributed blocks, with mining luck and labeling limitations, rather than directly counting ownership of machines.
Still, the broad picture is striking: a handful of pool labels account for most block production.
It is tempting to turn that into a claim that five companies own Bitcoin. That would confuse several different kinds of power.
A pool can coordinate machines owned by many independent businesses. Those businesses can redirect their computing power. And mining power cannot force a fully validating node to accept a block that violates the rules that node enforces.
Those protections matter. So does the decision that happens before the machines begin hashing.
A Bitcoin mining machine repeatedly hashes candidate block headers. The transaction selection behind that work has already happened.
In a conventional pool arrangement, the pool builds the candidate block template and distributes mining jobs. Participants supply the computational work. Pooling reduces the revenue uncertainty of waiting for a miner’s own machines to discover an entire block.
For a business with an electricity bill, that is a compelling service. The electricity supplier expects payment even during a long run of bad luck.
But the arrangement often bundles together two services: sharing mining rewards and choosing transactions.
That creates a concentration risk which a photograph of mining farms around the world cannot reveal.
You can have different owners, different buildings, and different electricity suppliers while a much smaller group chooses the payments those machines attempt to confirm.
The machines can be geographically distributed while transaction selection remains concentrated.
And we have already seen operators use that discretion.
A U.S. rollout planned for late October brings digital dollars into Samsung Wallet. The deeper battle is over who owns the customer when the blockchain fades from view.
On March 30, 2021, Marathon announced a mining pool intended to filter transactions according to its AML and OFAC compliance approach. Its release explicitly described excluding transactions involving listed addresses.
On May 31, the company announced that MaraPool would cease filtering transactions as it adopted Bitcoin Core 0.21.1 without modification.
The episode establishes an announced policy and its reversal. It does not establish that every small block the pool produced was evidence of censorship.
More direct evidence arrived later. In November 2023, Bitcoin developer b10c investigated six missing transactions involving sanctioned addresses. He identified likely innocent explanations for the Foundry and ViaBTC cases, while concluding that four F2Pool cases likely involved filtering. His subsequent update recorded an acknowledgment by F2Pool’s co-founder that a filtering patch had been used.
The transactions were ultimately mined by other participants.
That is the encouraging part: independent alternatives worked.
It is also where the harder question begins. A defense that depends on other miners being willing and able to include a payment needs those alternatives to remain meaningful.
What happens when the miners willing to include your transaction become the minority?
Subscribe to the free offer of In Bitcoin We Trust Newsletter to continue reading the articleBelow, I break down what widespread filtering would do to confirmation times, why switching pools is only part of the defense, and how Stratum V2 and DATUM can return transaction selection to miners. You’ll also get five questions to judge whether mining decentralization is improving.
