Zcash NU7 upgrade begins testnet phase with 25-second blocks
Zcash has activated its NU7 network upgrade on the testnet, marking a significant step toward faster block production and a new fee mechanism. The upgrade went live at block 4,465,026 on October 4, ahead of the initially estimated October 6 timeline. This testnet phase will run until October 20, when developers will review the results to decide whether to proceed with the mainnet activation, currently targeted for November 5.
The NU7 upgrade introduces several key changes, including reducing the target block spacing from 75 seconds to 25 seconds. This adjustment aims to decrease the average wait time for the first confirmation of a transaction. Alongside this, the upgrade includes a Network Sustainability Mechanism (NSM) that redirects part of transaction fees into future block rewards. Additionally, version 4 transactions will be disabled post-activation, which could leave ZEC in the legacy Sprout shielded pool unspendable if users do not move their funds beforehand.
Preparations for NU7 have been extensive, with developers and node operators testing the changes under real conditions. The Zcash Foundation released Zebra 7.0.0-rc.0 to support the upgrade, encouraging testnet operators to run the release candidate. The upgrade also includes new limits on shielded actions to protect wallets from spam as block production becomes more frequent. A private governance poll involving nearly 2.4 million ZEC showed overwhelming support for the changes, with over 99.9% of participants backing the 25-second block interval.
The NU7 upgrade follows the Ironwood upgrade, which addressed a vulnerability in the Orchard shielded pool. Ironwood introduced a separate shielded pool and accounting safeguards to prevent the creation of counterfeit ZEC. With NU7, Zcash continues to evolve its protocol, focusing on improved transaction efficiency and network sustainability.