Zcash has activated its NU7 network upgrade on the public testnet, putting a new 25-second block target and a redesigned transaction-fee mechanism into live consensus testing.
The activation occurred at Testnet block 4,465,026 on October 4, 2026, at 18:21:45 UTC, according to the reported activation data. The date came earlier than the October 6 estimate previously given for the upgrade, which was based on projected block production rather than a fixed calendar date.
The NU7 deployment specification identifies block 4,465,026 as the Testnet activation height. Mainnet has not activated the upgrade, and its activation height remains unset pending the next stage of the deployment process.
The most visible change is the reduction in Zcash’s target block interval from 75 seconds to 25 seconds. The change is defined in ZIP 218, which also adjusts several related consensus parameters rather than simply changing the block timer.
With the new target, a first block confirmation is expected to take about a third as long on average under normal conditions. The block subsidy is also reduced to account for the higher block frequency, keeping the rate of scheduled issuance broadly aligned with the previous timing model rather than producing three times as much ZEC.
NU7 also changes how transaction fees are handled. Under ZIP 235, 60% of transaction fees in a block are removed from circulation and placed into the Network Sustainability Mechanism reserve. The miner receives the remaining 40% of transaction fees.
The 60% rule applies to transaction fees, not the entire block reward. Miners continue to receive the scheduled block subsidy in addition to their permitted share of fees. The reserve is intended to support future block rewards as the regular subsidy declines through Zcash’s halving schedule.
The reserve is not scheduled to be paid back immediately. Under ZIP 237, Zcash retains its existing halving model and 21 million ZEC supply cap while providing for the later reissuance of ZEC held in the Network Sustainability Mechanism. The NU7 deployment specification places the Testnet reissuance point at block 7,305,222.
The fee change is separate from Zcash’s conventional fee calculation rules. Earlier work on ZIP 317 defines conventional transaction fees based on logical actions, while ZIP 235 determines how the fees collected under the new consensus rules are allocated between miners and the Network Sustainability Mechanism.
Faster blocks come with new shielded limits
NU7 also modifies the limits placed on shielded activity. ZIP 218 sets per-block limits including 330 Orchard actions, 330 Ironwood actions and 300 Sapling inputs and outputs, together with a global shielded-action budget. The general 2 MB block-size limit remains in place.
These restrictions were designed alongside the move to 25-second blocks. The upgrade is therefore not simply increasing block frequency and leaving every other processing constraint unchanged. The proposal’s analysis addressed the amount of work that shielded transactions could impose on nodes and wallets under heavier or adversarial workloads.
ZIP 218 also expands the difficulty-adjustment averaging window from 17 blocks to 102 blocks. The numerical window becomes larger because blocks are expected to arrive three times as often, allowing the adjustment process to operate over a longer sequence of blocks while accounting for the shorter target interval.
NU7 additionally disables version 4 transactions through ZIP 2003. Because the older Sprout shielded pool depends on the earlier transaction format, remaining Sprout funds will no longer be spendable through the existing protocol after the rule takes effect.
The software supporting the change has also moved into release-candidate testing. The Zcash Foundation published Zebra 7.0.0-rc.0 as the NU7-compatible release candidate for Testnet. The release includes the state-database changes required to record the Network Sustainability Mechanism reserve.
The deployment has been preceded by months of protocol and governance work. Community polling strongly favored retaining Zcash’s halving structure and moving to 25-second blocks, while the timing of the later Network Sustainability Mechanism reissuance generated more disagreement. Coinholder sentiment ultimately favored a 2031 start for the reserve’s reissuance.
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