Definition
Header-only mining (HOM) is the Stratum V2 mode used on standard channels, where a hashing device works only on the block header and never assembles transactions itself. The upstream node selects the transactions and computes the merkle root, then hands the device a fixed merkle root inside a standard job. The device's job is simply to grind the header fields it is allowed to change: the version, the nonce, and the nTime timestamp.
Why restrict the device this way
Keeping firmware to header-only work makes the mining device dramatically simpler and reduces the data it must hold and process, which suits the constrained controllers on ASIC hardware. The trade-off is search-space size: for one standard job with a fixed nTime, the spec notes the search space is roughly 280 terahashes before the device needs a fresh job with a new merkle root. A modern ASIC chews through that quickly, so the upstream node must keep feeding new jobs to keep the hardware busy.
Where the intelligence lives
Header-only mining does not mean the operator gives up transaction choice. In a self-hosted Stratum V2 stack the transaction selection happens upstream at the operator's own node and Job Declarator, then flows down to the device as standard jobs. So the device stays dumb and efficient while sovereignty over block content is preserved one layer up.
Header-only work is the defining limit of a standard Stratum mining channel; the merkle root it receives is ultimately derived from work built by the Template Provider.
In Simple Terms
Header-only mining (HOM) is the Stratum V2 mode used on standard channels, where a hashing device works only on the block header and never assembles…