Zcash NU7 goes live, cutting target block time to 25 seconds

Zcash’s NU7 upgrade activated on mainnet at block 3,543,405, setting a 25-second target between blocks instead of 75 seconds. The change is designed to shorten confirmation waits for users while keeping the network’s daily ZEC issuance essentially unchanged.

CoinDesk’s report on the activation says the block was mined at 02:34 UTC on Nov. 6. In the hours after, blocks averaged about 39 seconds apart as mining difficulty adjusted toward the new target. That early pace is a measure of the transition, not the steady-state target.

How much faster could a Zcash payment confirm?

At the target pace, the first confirmation could arrive in about 25 seconds on average, compared with 75 seconds before NU7. A service that waits for three confirmations could see its expected wait fall from nearly four minutes to about 75 seconds. Those are estimates based on block timing: each exchange, merchant or other service sets its own confirmation requirements, so users may not see the same reduction everywhere.

The shorter interval also changes how miners coordinate. Once a block is found, other miners need time to receive and verify it before building on it; less time between blocks can increase the chance that competing blocks are discarded. CoinDesk reports that testing by Zakura, Zcash node software, recorded 3.43% discarded blocks under demanding 25-second conditions, compared with 1.57% at the previous pace. The upgrade’s software changes include checks that reuse some transaction validation work to reduce repeated processing.

What changed for issuance, fees and older funds?

The block subsidy was cut to a third alongside the shorter block interval, so the rate of new ZEC issuance remains essentially unchanged. The number of blocks between halvings was tripled to preserve the existing halving schedule and the 21 million ZEC supply cap, according to the Zcash Foundation’s Zebra 7.0.0 release notes.

NU7 also activates the Network Sustainability Mechanism. Sixty percent of each block’s transaction fees go into a reserve, while miners receive the remaining 40%. The reserve is scheduled to begin returning to block rewards at height 8,939,664, expected in 2031. This changes how fees are allocated now and creates a future source of miner rewards as block subsidies decline.

There is a direct consequence for holders of funds in Sprout, Zcash’s original shielded pool: NU7 made version 4 transactions invalid, and Sprout transfers rely on that format. The Foundation says funds remaining there become unspendable. CoinDesk reports about 12,224 ZEC remained in the pool at activation; a possible recovery mechanism had been outlined, but none was approved as of its report.

What should users and operators watch next?

Wallet users can expect confirmation timing to depend on the service they use as the network settles toward the new block target. Node operators had to install NU7-compatible software before activation to remain on the consensus chain; the Foundation’s release notes say nodes that did not upgrade would follow a different chain. Services that process ZEC will also determine how many confirmations they require before crediting or releasing funds.

The next scheduled milestone for the fee reserve is block 8,939,664, when gradual reissuance is set to begin. Until then, the practical measure to watch is whether block timing moves toward the 25-second target and how services adapt their confirmation policies.

Sources

• CoinDesk’s report on the activation — coindesk.com
• Zcash Foundation’s Zebra 7.0.0 release notes — zfnd.org