Zcash activates NU7, cutting target block time to 25 seconds

Zcash activated its NU7 network upgrade on Friday, cutting the target time between blocks from 75 seconds to 25 and setting the stage for faster private payments. The change took effect at block 3,543,405, mined at 02:34 UTC, according to CoinDesk’s report on the NU7 launch.

By 04:59 UTC, the network had produced 225 more blocks, averaging about 39 seconds apart, CoinDesk reported, citing ZecStats. The target is not a guarantee for each block: mining difficulty was still adjusting to the new pace. Zcash hides the sender, recipient and amount in private payments, also called shielded transactions.

How does NU7 change payment waits?

With blocks targeted every 25 seconds, a payment could receive its first confirmation in about 25 seconds on average, compared with 75 seconds before the upgrade. A service that waits for three confirmations could see its expected wait fall from nearly four minutes to about 75 seconds, CoinDesk reported.

Those are network averages, not a promise of when a customer can spend or withdraw funds. Exchanges, merchants and other services set their own confirmation rules, so the wait depends on the service as well as block timing.

What does NU7 change for wallets?

The upgrade also limits how much shielded activity can go into each block. Wallets scan blockchain data to find payments meant for them, and those limits reduce the amount they may have to download in a worst-case day from 271 megabytes to 169 megabytes, according to Zcash’s ZIP 218 proposal.

The proposal estimates that the changes could more than double capacity for simple private payments, from about 2.9 to 6.6 per second. It sets caps on shielded activity in the Orchard, Ironwood and Sapling pools, and disables Sprout transactions. Orchard and Ironwood are pools used for private Zcash payments; Sapling and Sprout are older shielded pools.

That capacity figure is an estimate in the proposal, not a measure of payments already being processed. The upgrade aims to reduce waiting and limit the data wallets must scan, while the live network’s actual block pace and each service’s confirmation policy determine how quickly users see the change.

Sources and documents

• CoinDesk’s report on the NU7 launch — coindesk.com
• Zcash’s ZIP 218 proposal — zips.z.cash