Zcash activates NU7, cutting target block time to 25 seconds

Zcash activated its NU7 network upgrade on mainnet at block 3,543,405 on Nov. 5, cutting the target time between blocks from 75 seconds to 25 and changing how the network handles rewards and transaction fees, according to The Block’s report on the activation. A block is a batch of transactions that miners add to the chain. The shorter target means blocks are expected to arrive three times as often; it does not mean every block will take exactly 25 seconds.

How does NU7 make blocks arrive more often?

NU7 changes the target spacing in Zcash’s consensus rules: miners compete to add the next block, and the protocol sets the intended interval between successful blocks. Before the upgrade, that target was 75 seconds. It is now 25 seconds. The Zcash Foundation said the change is specified in ZIP 218 and is intended to cut the average wait for a first confirmation by about three times.

A confirmation is a transaction’s inclusion in a block. A recipient or wallet may require additional confirmations before treating a payment as final or available, so the shorter block target alone does not set every service’s payment policy. It changes the pace at which the chain can record transactions.

Why do block rewards change with the faster schedule?

Because blocks are targeted more frequently, NU7 divides the block reward by three. That keeps the amount of new ZEC issued per day essentially unchanged, according to the Zcash Foundation’s NU7 release notes. The upgrade also triples the number of blocks between halvings, which keeps the four-year halving schedule and the 21 million ZEC supply cap unchanged. Think of it as dividing the same daily issuance across more, smaller payments to miners.

The timing change is therefore not a threefold increase in the daily amount of new ZEC. It changes how often blocks and their smaller rewards arrive, while preserving the planned issuance pace.

What does NU7 change about transaction fees?

NU7 activates the Network Sustainability Mechanism, or NSM. It directs 60% of each block’s transaction fees into a public reserve and leaves the other 40% with miners. The reserve is scheduled to return gradually through block rewards starting at height 8,939,664, which the Foundation says is set out in ZIP 259. The mechanism is intended to provide a future source of mining rewards as block subsidies decline.

NU7 also makes version 4 transactions invalid. The Sprout shielded pool, Zcash’s original privacy pool, relies on that transaction format, so any funds left there cannot be spent under the new rules. The Block reported that about 12,224 ZEC remained in Sprout at activation. Together, the faster target, adjusted rewards and fee reserve change the chain’s operating rules while leaving its supply cap intact.

Source material

• The Block’s report on the activation — theblock.co
• the Zcash Foundation’s NU7 release notes — zfnd.org