Zcash’s NU7 upgrade is now live on the network’s public testnet, cutting the target time between blocks from 75 seconds to 25 seconds. The activation block arrived two days earlier than the Zcash Foundation’s release notes estimated.
The upgrade has no mainnet activation height yet, and developers are scheduled to set one on October 20. The draft deployment proposal also states that NU7 invalidates the only transaction format that can move funds out of Sprout, Zcash’s original shielded pool.
According to the ZecBlock testnet explorer, block 4,465,026, NU7’s scheduled activation height on testnet, was mined on October 4, 2026, at 18:21:45 UTC. Its block hash is 000089ba27100beede16d64b34e3d1b626b428cb7ee9fe6dcfdc217ce24e78af. Zcash confirmed the activation in a post on X.
What Block 4,465,026 Shows
A testnet is a parallel copy of a blockchain that uses tokens with no market value. Developers use it to trial rule changes before they reach the main network. On Zcash’s testnet, the native token is called TAZ instead of ZEC.
The Zcash Foundation’s Zebra 7.0.0-rc.0 release notes set testnet activation at height 4,465,026 and estimated it would arrive around Oct. 6. The release is a release candidate, and it sets no mainnet activation height.
Testnet operators had to upgrade before the activation block to stay on the NU7 chain. Zebra, the Rust node software maintained by the Zcash Foundation, is the node implementation that carries the upgrade.
What NU7 Changes, According to ZIP 259
The rules for the upgrade are set out in ZIP 259, a Zcash Improvement Proposal. It was created on Sept. 15 and is still marked “Draft.” According to the document, NU7 cuts the block target spacing to 25 seconds under ZIP 218. It also sets limits on shielded transaction actions, both per pool and across the whole network.
ZIP 259 says the action limits cap the validation and synchronization costs that more frequent blocks would otherwise create. The proposal states that NU7 introduces no new transaction format: version 5 and version 6 transactions remain valid.
The document also records that NU7 does not follow ZIP 200‘s guidance to schedule network upgrades after the last supporting node reaches its end-of-support halt.
Sprout Funds and the End of Version 4 Transactions
Under ZIP 2003, NU7 makes version 4 transactions invalid. ZIP 259 states that Sprout transfers can only be represented as version 4 transactions. As a result, any funds still in the Sprout pool become unspendable once NU7 activates.
Sprout was the shielded pool Zcash launched with in 2016. A shielded pool holds ZEC in transactions whose amounts and addresses are encrypted.
Because no mainnet activation height has been set, the deadline for moving Sprout funds on the main network is not yet fixed.
How 60% of Fees Leave Circulation
NU7 also deploys ZIP 235, which removes 60% of transaction fees from circulation. It pairs this with ZIP 237, a version of the Network Sustainability Mechanism (NSM) that keeps Zcash’s existing halving schedule.
ZIP 259 says the removed amounts are tracked as the “NSM Value Balance.” That balance is public consensus state, cannot be spent, and is not counted in issued supply. The proposal states that the changes do not raise the ZEC supply cap, because any funds later paid out of that balance were removed from circulation in equal amount first.
On testnet, reissuance from the balance is set to begin at block height 7,305,222. The mainnet reissuance height will be calculated from the mainnet activation height once it is assigned.
The Zebra release notes also say NU7 seeds the mainnet reserve with 36,858,445,520 zatoshis, about 368.58 ZEC. A zatoshi is one hundred-millionth of a ZEC. The release notes describe this amount as the historical pre-NU6 shortfall.
The Road to the October 20 Mainnet Decision
ZIP 259 lists the mainnet activation height as “TBD (To be set on OCT 20)” and requires it to be a multiple of three. The Crypto Times reported in September that developers had agreed on November 5 as the target date for mainnet activation.
Coinholder and community polls held in August and September asked five questions about NU7’s scope, according to ZIP 259. The document states the polls did not reach a shared majority on when NSM reissuance should begin. Full results are posted on the Zcash Community Forum.
ZIP 259 lists three open items: assigning the mainnet activation height, publishing the mainnet reissuance height, and adding reference implementations and test vectors for the NSM Value Balance.
How NU7 Fits After Ironwood
NU7 follows NU6.3, known as Ironwood. According to the Zebra 6.0.0 release notes, Ironwood was scheduled to activate on mainnet at block height 3,428,143, around July 28. Ironwood introduced the version 6 transaction format.
ZIP 259 states that NU7 avoids a new transaction format partly to limit disruption to software that reads transactions and to wallets, coming directly after version 6 was introduced.
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