Zcash NU7 goes live on testnet with 25 second blocks

Zcash has activated its NU7 network upgrade on testnet at block 4,465,026, putting its planned 25 second blocks and new fee mechanism into live testing ahead of a targeted Nov. 5 mainnet rollout.

According to Zcash testnet block data, the activation block was mined on Oct. 4 at 18:21:45 UTC, earlier than the roughly Oct. 6 timing developers had previously estimated. Zcash later confirmed that NU7 was live on testnet.

Testing now gives developers several weeks to observe the protocol changes before deciding whether the same upgrade should move to the main network. A final decision is scheduled for Oct. 20, when developers are expected to determine the mainnet activation height based on the testnet results.

Mainnet activation remains targeted for Nov. 5 and has not yet been finalized.

Zcash NU7 begins testing with 25 second blocks

NU7 would cut Zcash’s target block spacing from 75 seconds to 25 seconds, allowing the network to produce roughly three blocks during the period currently targeted for one.

Zcash Foundation said in its Oct. 2 release of Zebra 7.0.0-rc.0 that the shorter interval would reduce the average wait for a first confirmation from 75 seconds to 25 seconds. Testnet operators were encouraged to run the release candidate and test the upgrade “under real conditions.”

Mainnet operators were told they did not need to make changes yet because no activation height had been established.

The testnet rollout follows weeks of preparation for the upgrade. As crypto.news previously reported, Zcash engineering teams agreed in September on the proposed NU7 package and targeted Nov. 5 for its mainnet deployment after completing the testnet phase.

Alongside faster blocks, NU7 introduces new limits on shielded actions designed to control the amount of work that can be included in individual blocks. Zcash Foundation said the limits are intended to protect wallets from spam while block production becomes more frequent.

The proposed timing change received strong backing from ZEC holders before the upgrade schedule was set. A private governance poll involving nearly 2.4 million ZEC found that roughly 99.9% of participating coins supported reducing the target block interval to 25 seconds.

Participation represented roughly 66% of the eligible Ironwood balances recorded for the vote. Around 98.9% supported keeping Zcash’s existing halving schedule, while approximately 96.6% backed February 2031 for the start of reissuance under the Network Sustainability Mechanism.

Reducing the interval between blocks does not triple the amount of ZEC issued over the same period. NU7 adjusts issuance alongside the shorter block schedule so that producing more blocks does not result in miners receiving three times as much ZEC each day.

NU7 introduces a new Zcash fee mechanism

Another major part of the upgrade is the Network Sustainability Mechanism, or NSM.

Under the mechanism, part of each transaction fee is removed from immediate circulation and placed into a reserve that can be used for future block rewards. The Zcash Foundation described the system as recycling part of transaction fees into later issuance.

NU7 would also disable version 4 transactions once the changes reach mainnet.

The change has consequences for ZEC still held in Zcash’s older Sprout shielded pool because spending from Sprout relies on version 4 transactions. Funds remaining there would become unspendable after NU7 activation unless holders move their ZEC beforehand.

No such mainnet change has occurred yet. The current activation applies only to Zcash’s public test network, where developers and operators can observe how the new consensus rules behave before the Oct. 20 decision.

Zcash has been preparing its node infrastructure for the change as well. Zebra 6.4 releases in September included work connected with NU7 preparation, while the release candidate issued on Oct. 2 added support for the upgrade on public testnet.

The network dealt with a separate Zebra problem shortly before those preparations. A high severity vulnerability affecting Zebra versions 6.4.0 and 6.4.1 could have allowed a peer to remotely crash a node. Zcash Foundation released Zebra 6.4.2 on Sept. 25 and said the issue affected node availability but did not affect consensus or funds.

Gemini had meanwhile moved its Zcash infrastructure to Zakura ahead of NU7. The exchange said its Zakura deployments reached the chain tip in a little over six hours, compared with close to one day for Zebra, while customer deposits and withdrawals continued operating normally.

NU7 follows Zcash’s Ironwood upgrade

NU7 arrives only a few months after Zcash completed another major protocol change prompted by a vulnerability in its Orchard shielded pool.

The Ironwood network upgrade activated on July 28 at block 3,428,143 and introduced a separately tracked shielded pool after developers dealt with a flaw that could theoretically have allowed undetectable counterfeit ZEC to be created.

Researchers had not found evidence that the Orchard vulnerability was exploited. Zcash’s privacy model, however, meant developers could not conclusively prove that unauthorized coins had never been created inside the affected shielded pool.

Ironwood addressed the supply uncertainty by separating the new pool from Orchard and introducing accounting safeguards governing how much ZEC could leave the older pool. Orchard was left available for withdrawals while newly shielded funds moved into Ironwood.

Zcash Foundation’s Zebra 6.0.0 release implemented the new pool using Orchard’s Action structure and Halo2 proof system while maintaining separate records for its note commitment tree, nullifier set, chain value pool and chain history.

The upgrade followed emergency measures taken in June after the Orchard flaw was discovered. Developers temporarily disabled affected transactions before deploying corrected software and later moved toward Ironwood as the longer term response.

NU7 now represents the next stage of the network’s protocol schedule, with the current testnet activation focused on block timing, transaction rules, shielded action limits and the new sustainability mechanism.

Developers are scheduled to review the testnet experience and make their mainnet decision on Oct. 20. If they proceed, an activation height will be set for the production network, with Nov. 5 remaining the targeted date for NU7 to go live on Zcash mainnet.