Who Builds and Controls the Block?
Most miners set up their rig, pick a pool, and start hashing without ever asking one of the most important questions in the process: who decides what goes into the block? It seems like a technical detail buried somewhere in the background, but it sits at the center of something much bigger than mining fees or payout structures. It touches on what Bitcoin is supposed to be and whether the way mining is practiced today lines up with that.
When a block gets added to the Bitcoin blockchain, it is not just a random collection of pending transactions. Someone had to choose which transactions go in, in what order, and which ones get left out. That selection is called the block template, and it is built before any hashing begins. The miner’s job, at its most basic level, is to take that template and find the valid hash that seals it. What most miners in large pools do not always realize is that they are hashing a template someone else constructed.
In the early days of Bitcoin, individual miners built their own templates. They ran full nodes, they saw the mempool, the waiting area where unconfirmed transactions sit, and they decided what to include. That process was inherently decentralized because every miner made their own choices. As mining grew more competitive and individual miners joined pools to smooth out their income, something quietly shifted. Pools took over template construction because it was simpler and more efficient. Miners contributed hashrate. The pool handled everything else, including deciding what went into the block.
This is how most large mining pools operate today. Foundry USA, AntPool, and F2Pool together represent a substantial portion of Bitcoin’s total hashrate. Each of them constructs block templates centrally. Miners who point at these pools are essentially renting out their computing power, while the pool makes the editorial decisions about which transactions get confirmed. For most miners, this has never been a problem in practice. The pools follow standard transaction selection rules, prioritizing higher-fee transactions as intended by the protocol. The system works, and payouts arrive on schedule.
But efficient and decentralized are not the same thing, and that gap matters more than it might appear.
Ocean Pool has taken a different approach. Rather than constructing templates for all its miners, Ocean gives miners the option to build their own. To make this possible, Ocean developed an open protocol called DATUM, which stands for Decentralized Alternative Templates for Universal Mining. DATUM allows a miner running their own full node to request and construct their own block template rather than accepting the one the pool provides. A miner using DATUM independently monitors the mempool and decides which transactions to include in the block they are hashing. The pool still coordinates the work and handles payouts, but the editorial control stays with the miner. It is closer to how Bitcoin was originally designed to function, and because DATUM is an open protocol, it is not exclusive to Ocean. Other pools could adopt it, meaning it represents not just one pool’s policy but also a potential direction for the broader mining industry.
The reason this distinction matters goes beyond preference. It comes down to a question that sounds hypothetical until it isn’t: what happens if someone applies pressure to the pools that control the templates?
Bitcoin’s mempool contains all kinds of transactions. Some are straightforward transfers between individuals. Some interact with protocols or services that might attract regulatory attention in certain jurisdictions. If a government or regulatory body were to approach a large mining pool and require that certain types of transactions be excluded from their templates, that pool would have the technical ability to comply quietly and at scale. Miners pointed at that pool would be unknowingly participating in a filtered version of Bitcoin, one where not all valid transactions are treated equally. The blockchain would keep growing. Blocks would keep getting found. But the promise of a neutral, permissionless system would be quietly eroding beneath the surface.
This is not a prediction. No major pool has done this openly, and the Bitcoin community would respond forcefully if it became known. But the architecture for it exists wherever template construction is centralized. The template is the lever, and concentrated control of that lever is a structural vulnerability regardless of whether anyone chooses to pull it today.
This is precisely what Satoshi Nakamoto’s design was meant to prevent. The white paper described a system where transaction validation and block construction would be distributed across a wide network of independent participants. No single node, no single miner, and no single pool would be able to decide what gets confirmed and what doesn’t. The security of the network was never just about hashrate. It was about the distribution of decision-making. A network in which thousands of independent miners each build their own templates is far more resistant to external pressure than one in which a handful of companies quietly handle that job for everyone.
For a miner weighing this decision today, the practical tradeoff is real. Joining a large pool with centralized templates is simpler. The infrastructure is mature, the payouts are reliable, and you do not need to run your own node or manage any additional software. Choosing a pool like Ocean and opting into self-constructed templates via DATUM takes more setup and more engagement with how Bitcoin actually works under the hood. For a beginner, that learning curve is not trivial.
But understanding the tradeoff is worth the effort even if you do not act on it immediately. The choice of where to point your hashrate is a vote, whether you think of it that way or not. Hashrate pointed to a pool that centralizes template construction, which hashrate reinforces as the model. Hashrate pointed at a pool that distributes template control, and hashrate is pushing in the other direction. Neither choice is invisible to the network.
Bitcoin has survived and grown because the incentives built into its design have, so far, kept the most important decisions distributed. Miners earn more by following the rules than by breaking them. But incentives are not the same as guarantees, and the creeping centralization of template construction is the kind of gradual shift that tends to go unnoticed until it is deeply embedded. The miners who understand this today are in a position to make a deliberate choice rather than a default one.
Satoshi did not build a system meant to be managed by a small number of companies making quiet decisions about what gets confirmed. The original vision was a network in which every participant with a node and a miner had an equal voice in the process. Template construction is where that voice either gets exercised or handed off. Knowing which one you are doing is the beginning of mining with intention.
If you’re still getting started and want to understand more about how Bitcoin works at the foundational level, refer to our FREE UTXO Tracker and The Jar On The Counter: A Beginner’s Guide To Bitcoin UTXOs.