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Zcash activates NU7, cutting target block time to 25 seconds

Zcash activated NU7, cutting target blocks to 25 seconds and expanding shielded capacity, while changing fee rules and making old Sprout funds unspendable.

The eCrypto Desk

Zcash activates NU7, cutting target block time to 25 seconds

Zcash, a cryptocurrency whose shielded transactions can hide the sender, recipient and amount, activated its NU7 network upgrade at block 3,543,405 on Nov. 6. The change cuts the target time between blocks from 75 seconds to 25, aiming to shorten confirmation waits for private payments.

According to CoinDesk’s report on NU7’s activation, the network mined the activation block at 02:34 UTC. In the following hours, blocks averaged about 39 seconds apart as mining difficulty adjusted; 25 seconds is the new target, not a guarantee that every block will arrive on schedule.

For a merchant or exchange, the difference is measured in confirmation waits. A first confirmation could take about 25 seconds on average under the new target. A service that waits for three confirmations could expect roughly 75 seconds instead of nearly four minutes. Each service sets its own confirmation requirements, so users’ funds may not become available as quickly as the target interval suggests.

How much more shielded activity can NU7 handle?

NU7 raises the potential capacity for simple private payments while limiting activity that can burden wallets. The Zcash Foundation’s Zebra 7.0.0 release notes say the new per-block limits more than double Orchard throughput, from 2.9 to 6.6 transactions per second. Orchard is one of Zcash’s shielded pools.

The limits also address the work light wallets do to scan the chain for payments meant for them. According to the Foundation, they cut by about 37% the worst-case sync bandwidth that a spammer could impose on light wallets. The capacity figure describes what the protocol can accommodate; it does not show how many people are currently making private payments.

The faster target required changes to how blocks propagate between miners, since shorter intervals leave less time for the network to share each block before the next one is found. CoinDesk reported that NU7’s node software was tested on 80 computers across 11 regions. Under tests with blocks filled with transactions, 3.43% of blocks were discarded at the 25-second pace, compared with 1.57% at 75 seconds. That is a reported test result, not a measure of the live network’s long-term performance.

What changes for miners and older Zcash funds?

NU7 changes how transaction fees are handled: miners receive 40% of each block’s fees, while the other 60% is removed from circulation and placed in a reserve for future block rewards. The Foundation says the reserve is scheduled to begin reissuing funds at block 8,939,664; CoinDesk reports that this is expected around February 2031. NU7 also adjusts block rewards and halving intervals to preserve the existing issuance rate and 21 million ZEC supply cap.

There is a cost for holders of funds left in Sprout, Zcash’s original shielded pool. NU7 disables version 4 transactions, the only transaction format Sprout supports, so approximately 12,224 ZEC remaining there at activation became unspendable. CoinDesk reported that no recovery mechanism had been approved as of activation.

The next performance check is whether block times settle toward the 25-second target as mining difficulty adjusts. For the reserve mechanism, the longer-term milestone to watch is block 8,939,664, when scheduled fee reissuance is due to begin.

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