Zcash activates NU7, cutting target block time to 25 seconds

Zcash activated its NU7 upgrade at block 3,543,405 on Nov. 6 at 02:34 UTC, reducing the target time between blocks from 75 seconds to 25. The change is intended to shorten waits for private payments; as CoinDesk reported, actual confirmation times and when a payment can be used still depend on the service handling it.

The new interval is a protocol target, not a guarantee that every payment clears in 25 seconds. A merchant accepting a first confirmation could see a shorter wait, while exchanges and other services set their own confirmation requirements. For a service requiring three confirmations, the expected interval falls from nearly four minutes to about 75 seconds if blocks arrive at the new target.

How does NU7 increase shielded payment capacity?

NU7 combines shorter block spacing with limits on how much shielded activity can be included in each block. According to CoinDesk’s account of the upgrade, those limits reduce the worst-case daily data a light wallet may need to download from 271 megabytes to 169 megabytes. That matters because wallets scan the chain to find payments addressed to their users; unrestricted transaction activity can make that scan heavier.

The NU7 deployment specification, ZIP 259, schedules the network changes, while CoinDesk reports that the model estimates simple private-payment capacity rising from about 2.9 to 6.6 transactions per second. These are modeled capacity figures, not a measure of realized demand or throughput after activation.

Shorter spacing also leaves less time for newly mined blocks to reach other miners before the next block is found. CoinDesk reported that in testing across 80 computers in 11 regions, with blocks filled with transactions, 3.43% of blocks were discarded at the 25-second pace, compared with 1.57% at 75 seconds. The same report said that shortly after activation, the network’s first 225 subsequent blocks averaged about 39 seconds apart as mining difficulty adjusted. That early average was still above the new target.

What changes for miners and ZEC issuance?

NU7 directs 60% of each block’s transaction fees to a public reserve, leaving miners the other 40%. CoinDesk reports that the reserve is scheduled to begin supplementing block rewards around February 2031. The upgrade also reduces the reward per block by a third and triples the number of blocks between halvings, preserving the existing roughly four-year halving schedule and 21 million ZEC supply cap.

This shifts some fee value away from miners’ immediate earnings toward a later source of mining rewards, as block subsidies decline. The reserve does not increase the supply cap, but its future role depends on the scheduled reissuance and how the network’s fee activity develops.

Which users face the clearest cost of the upgrade?

Owners of funds in Zcash’s original Sprout privacy pool face the sharpest consequence: NU7 disables version 4 transactions, the only format Sprout can use, so remaining Sprout funds cannot be spent under the new rules. CoinDesk reports that about 12,224 ZEC remained there at activation; co-founder Sean Bowe has described a possible recovery mechanism, but none has been approved.

For most users, the practical signals to watch are whether wallets, exchanges and payment services have adopted compatible software, how block times settle as mining difficulty adjusts, and whether shielded activity approaches the modeled capacity. The upgrade’s faster target is in place; how much of that speed users experience depends on both network performance and service confirmation policies.

Sources and documents

• CoinDesk reported — coindesk.com
• NU7 deployment specification, ZIP 259 — zips.z.cash