Zcash activates NU7, cutting target block time to 25 seconds

Zcash activated its NU7 network upgrade at block 3,543,405 on Nov. 5, cutting the target time between blocks from 75 seconds to 25 and speeding up the first confirmation for private payments. The change also redirects most transaction fees to a public reserve for future mining rewards, according to The Block’s report on NU7’s mainnet activation.

• Target block interval: 25 seconds, down from 75.
• Transaction fees sent to the reserve: 60%; miners keep 40%.
• Activation height: 3,543,405.
• ZEC remaining in the Sprout pool at activation: about 12,224.

How does NU7 make private payments faster?

NU7 lets Zcash add a new block about three times as often, so a payment can receive its first confirmation sooner. A block is a batch of transactions added to the chain; a shielded payment hides the sender, recipient and amount from public view. The Zcash Foundation’s Zebra 7.0.0 release notes say the average wait for a first confirmation falls from 75 seconds to about 25.

That is a target interval, not a guarantee that every payment will confirm in exactly 25 seconds. The payment still needs to reach a block, and wallets, exchanges and merchants may require more than one confirmation before treating it as final. For someone who accepts a payment after its first confirmation, the shorter target could mean a shorter wait.

The upgrade also increases the modeled capacity for simple transfers in Zcash’s Orchard shielded pool from 2.9 to 6.6 transactions per second. It sets limits on activity in Orchard, Ironwood and Sapling, which the Foundation says reduce the worst-case data load on light wallets by about 37%.

What happens to issuance and transaction fees?

NU7 reduces each block’s reward in proportion to the faster block schedule, while tripling the number of blocks between halvings. The Foundation says those changes preserve the roughly four-year halving cycle, the existing rate of new ZEC issuance and the 21 million coin supply cap.

The Network Sustainability Mechanism puts 60% of each block’s transaction fees into a public reserve; miners receive the other 40%. The reserve is intended to support future mining rewards, with gradual payouts scheduled to begin at block 8,939,664, expected in 2031. The Foundation says the reserve also starts with funds from block rewards and fees miners left unclaimed before the NU6 upgrade.

Which older Zcash funds are affected?

NU7 makes version 4 transactions invalid. Because Zcash’s original Sprout shielded pool can only use that transaction format, any funds left there cannot be spent under the new rules. The Block reported that about 12,224 ZEC remained in Sprout at activation.

Node operators had to run NU7-compatible software to stay on the consensus chain after activation. Most wallet users do not need significant changes, according to The Block, but the effect on funds in Sprout is direct: those transactions can no longer be made under the upgraded rules.

Sources and documents

• The Block’s report on NU7’s mainnet activation — theblock.co
• Zebra 7.0.0 release notes — forum.zcashcommunity.com