Zcash NU7 Prepares for Testnet With a 25-Second Block Target
Zcash’s NU7 upgrade aims to cut target block spacing from 75 seconds to 25. A Zebra release candidate asked public Testnet operators to prepare for activation, but did not confirm that activation had happened or set a Mainnet date.
- NU7 targets one block every 25 seconds, down from 75.
- The planned public Testnet activation point was height 4, 465, 026.
- The upgrade also changes fee handling and shielded-transaction limits.
- The release announcement set no Mainnet activation height.
What the Testnet announcement confirms
The Zcash Community Forum post “Zebra 7.0.0-rc.0: NU7 Arrives on Testnet” calls Zebra 7.0.0-rc.0 the first release candidate for NU7. Zebra is node software, while NU7 is the network upgrade. The post asked public Testnet operators to upgrade ahead of the network’s planned activation at block height 4, 465, 026, expected around October 6. The excerpt does not specify the year.
A planned activation does not confirm that activation took place. The release notice reports neither a completed activation nor observed Testnet results. It also says that no Mainnet activation height had been set, so the release candidate was not a Mainnet deployment schedule.
What 25-second blocks could mean
Under ZIP 218, NU7 changes Zcash’s target block spacing from 75 seconds to 25. If a transaction is included promptly, the shorter target should reduce the expected wait for its first confirmation. Zebra says that wait is expected to drop from 75 seconds to 25. Actual block intervals vary, though, and a transaction may have to wait for inclusion.
A target is not a stopwatch. And one confirmation does not make a payment instantly irreversible. Exchanges, merchants and bridges may require more confirmations under their own risk policies.
Zebra says scheduled ZEC issuance is intended to continue at the same pace. NU7 triples the remaining halving intervals, measured in blocks, and divides each scheduled block reward by three. Since target block spacing also falls to a third, the intended time between halvings stays roughly the same. Issuance on any given day can vary with block production. The release says the four-year halving schedule and 21 million ZEC supply cap remain unchanged.
NU7 also changes how transaction fees are handled
The upgrade introduces a Network Sustainability Mechanism (NSM). Under ZIP 235, 60% of transaction fees from each block goes into a reserve, while miners keep the other 40%. Under ZIP 237, a predictable portion of the reserve is reissued with the normal block reward in each block.
The mechanism reallocates transaction fees. It is separate from creating new ZEC through issuance. Its stated goal is to prepare for a future in which block rewards decline and fees play a larger role in network security. The announcement says the public reserves will initially be seeded with the historical shortfall from before NU6, but does not explain the calculation in enough detail to assess its effect. It also does not establish how the mechanism will affect miner incentives or security in practice.
Shielded transaction limits and software changes
NU7 revises per-block limits for Orchard, Ironwood and Sapling, Zcash’s shielded transaction pools. It also prohibits new Sprout JoinSplits, a transaction mechanism used by the older Sprout pool.
The Zebra release announcement says the changes more than double Orchard protocol throughput and cut the worst-case light-wallet synchronization load from spam by about 37%. These figures describe protocol capacity and an estimated worst-case load, not independently verified performance in real-world conditions. The announcement gives no test methodology for the 37% estimate. A separate report calls NU7 a performance leap, but the release’s estimates have not been verified in real-world use.
The upgrade also has compatibility implications. The release candidate moves Zebra’s state database to format v29. The announcement says Zallet’s Zebra backend and Zaino’s Zebra read-state backend need compatible builds. It also warns that downgrading is unsupported after the database migration. Operators should check compatibility and the project’s upgrade guidance before moving to the release candidate. The announcement does not provide a specific backup procedure.
Key questions about Zcash NU7
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Did NU7 activate on public Testnet?
The release announcement scheduled activation at height 4, 465, 026, but does not confirm that it happened.
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What does the 25-second target mean?
It is the intended interval between blocks, not a guarantee of exact timing or final settlement after one confirmation.
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Is a Mainnet launch scheduled?
The release announcement set no Mainnet activation height.
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Does faster block spacing increase ZEC issuance?
Zebra says the scheduled issuance pace is intended to remain unchanged, along with the halving schedule and 21 million ZEC cap.
NU7’s shorter target spacing could reduce transaction wait times, but faster blocks are only one part of the upgrade. The release candidate also changes fee allocation, shielded-transaction limits and software compatibility. The release announcement did not establish whether the planned Testnet changes would perform as intended or when they might reach Mainnet.
