Crypto glossary
Stratum V2
Stratum V2 is an upgraded mining protocol that encrypts traffic between miners and pools and lets miners choose the transactions in the blocks they mine.
Since 2012, most miners have connected to pools with the original Stratum protocol, which sends work in plain text and lets the pool decide which transactions go into each block. Stratum V2, developed by a group of mining companies and open-source contributors, replaces it with an encrypted, more efficient binary protocol.
Encryption prevents hashrate hijacking, an attack in which someone intercepts the connection and redirects a miner's work. The binary format reduces bandwidth and latency, which matters for operations in remote places. The most important change is job declaration: miners can build their own block templates from their own node and only use the pool for payouts, taking back the power to decide which transactions are included.
That shift would make Bitcoin more censorship resistant, since a handful of pool operators would no longer control transaction selection for most of the hashrate. Adoption has been gradual: pools and firmware must support it, and many miners have little incentive to run their own nodes. Some new pools offer it as a selling point.
Example
A mid-size miner switches to a pool with Stratum V2 and job declaration, builds templates from its own Bitcoin Core node, and includes transactions the pool operator might otherwise have excluded.