Zcash tests 25-second blocks ahead of planned November upgrade

Zcash activated its NU7 upgrade on public testnet at block 4,465,026, cutting the target time between blocks from 75 seconds to 25 ahead of a planned November mainnet rollout. The earlier activation gives node operators, wallet developers and other infrastructure providers time to check the new rules before they affect real ZEC. CoinDesk reports that the activation came ahead of schedule; the Zcash Foundation’s Zebra release announcement had forecast it around October 6.

The shorter target could reduce confirmation waits for payments and exchange deposits, but it does not guarantee that every block arrives exactly on schedule. CoinDesk notes that actual block times vary. NU7 also changes fee handling, mining rewards and support for older privacy features, making the public test a rehearsal for more than speed.

How much faster should confirmations become?

NU7 sets the target block interval at one-third of its previous 75 seconds. The Foundation says that would reduce the average wait for a first confirmation from 75 seconds to 25. For a service that waits for three confirmations, CoinDesk calculates a target wait of about 75 seconds, down from 225 seconds, assuming the service keeps the same confirmation requirement.

That is a change in expected timing, not a promise of instant settlement. Block production varies, and applications still decide how many confirmations they require before treating a payment as accepted. Faster blocks may make waits shorter for merchants and exchanges, while the number of confirmations a service considers sufficient remains a separate operational choice.

The testnet provides a place to evaluate the change using coins without monetary value. The Foundation said its Zebra 7.0.0-rc.0 release was built for the NU7 trial and urged testnet operators to upgrade to remain on the upgraded chain. CoinDesk reported that both major node programs support the trial, with Zakura’s implementation released October 1 and Zebra’s test version published the next day.

What changes alongside the block schedule?

NU7 adjusts issuance so faster blocks do not mean three times as many new coins. The Foundation says Zebra divides each scheduled block reward by three and triples the remaining halving intervals, keeping the amount of ZEC issued per day unchanged. It also says the four-year halving schedule and 21 million ZEC supply cap remain unchanged.

The upgrade also introduces a Network Sustainability Mechanism: 60% of each block’s transaction fees go into a reserve for future mining rewards, while miners keep 40%. According to the Foundation, the reserve will reissue a predictable portion alongside normal rewards. The design redirects some fees from miners now to support future rewards as newly issued ZEC declines; its performance and effects on mining incentives are among the issues the test can help operators assess.

There is a compatibility cost for some users. NU7 disables transactions using Sprout, Zcash’s oldest private-payment system. CoinDesk reports that holders with funds there will need to move them before mainnet activation to retain the ability to spend them through the existing system. The trial therefore tests a faster schedule and new reward rules while also requiring affected holders and services to prepare for a legacy feature’s removal.

What must happen before NU7 reaches mainnet?

Testnet activation does not itself put the upgrade on mainnet. CoinDesk reports that developers plan to review test results and decide on mainnet activation October 20; November 5 remains the target, and no mainnet activation block has been set. The Foundation likewise said in its announcement that no mainnet height had been set and that its Zebra build was a release candidate, not a stable release.

The next signals are whether operators report problems with the upgraded testnet, whether developers proceed after their October 20 review, and whether a mainnet activation height is published. Until then, the 25-second target is a testnet change, and the November date remains a plan rather than a confirmed launch.

Sources and documents

• Zcash Foundation’s Zebra release announcement — forum.zcashcommunity.com