ASICBoost

ASICBoost is a proof-of-work optimization, invented by Timo Hanke and Sergio Demian Lerner in 2016, that exploits a structural quirk in Bitcoin's double-SHA256 algorithm. By arranging work so that part of the hashing computation can be reused across many candidate headers, an ASIC performs fewer total operations per share, cutting energy consumption by roughly 15 to 30 percent depending on implementation.

Covert versus overt

There are two ways to apply the trick. Covert ASICBoost manipulates the Merkle root by grinding the transaction ordering; it is hard to detect but carries harmful side effects, including an incentive to limit block size, and it is fundamentally incompatible with the secondary commitments that SegWit blocks require. Overt ASICBoost instead rolls bits in the block header's version field, is plainly visible on-chain, and has none of those negative incentives. The industry's standardization of overt version rolling through BIP 310 was a direct response to the controversy around the covert form.

Practical relevance today

Most modern ASICs support overt ASICBoost, and miners enable it through their pool's version-rolling negotiation rather than any special hardware mode. The energy savings compound across a fleet, making it a meaningful efficiency lever for any operation tracking joules per terahash. Because the covert form clashes with SegWit, overt rolling is now the only practically relevant variant on Bitcoin.

The header mechanism that enables overt ASICBoost is covered in our Version Rolling (BIP 310) entry.