Zcash's NU7 Upgrade Activated, Private Payments Confirm 3x Faster

Zcash activated NU7 early Friday, reducing the target block interval to 25 seconds from 75 seconds so private payments can confirm three times faster. Block 3,543,405 marked activation and was mined at 02:34 UTC. ZecStats recorded 225 additional blocks by 04:59 UTC, with an average interval of about 39 seconds. Mining difficulty, which controls the difficulty of producing blocks, continued adjusting to the shorter target interval.

Zcash payments conceal the identities of senders and recipients, along with payment amounts. Quicker confirmations could improve payment usability for shops, exchanges and transfers between blockchains. A merchant could receive an initial payment confirmation after an average of about 25 seconds. An exchange that requires three confirmations could see the expected delay fall to about 75 seconds from nearly four minutes. Individual services determine confirmation requirements, so customers' access to funds also depends on the service processing each payment.

Miners must receive and validate a newly discovered block before working on the following block. Another miner can create a competing block during that delay, and the network eventually discards the competing block. Shorter block intervals give miners less time to receive and validate blocks. Network developers Valar Group and Project Tachyon built the Zcash node software Zakura. Zakura tested the 25-second interval using transaction-filled blocks on 80 computers across 11 regions. The tests produced a discarded-block rate of 3.43%, versus 1.57% with the previous 75-second interval.

Zakura engineers also changed transaction validation to avoid repeating some work. The software retains parts of the checks performed when a transaction arrives and reuses those results when the transaction enters a block. The software still repeats checks tied to current account balances and blockchain history.

NU7 restricts the amount of private transaction activity allowed within a block. Wallets search the blockchain for incoming payments, so transaction flooding can increase the processing required of every wallet. The upgrade specification puts the maximum daily download requirement at 169 megabytes, down from 271 megabytes. The specification estimates that the limits and more frequent blocks could raise simple private payment capacity from about three per second to more than six.

Miners now collect 40% of transaction fees. The other 60% is taken out of circulation and tracked in a reserve that begins contributing to future block rewards around February 2031. The arrangement maintains Zcash's supply ceiling of 21 million coins.

NU7 retired Sprout, the original Zcash privacy pool introduced in 2016, making about 12,224 ZEC unspendable. Co-founder Sean Bowe has described a potential recovery mechanism. No recovery mechanism had received approval as of Friday.