Zcash activated its NU7 network upgrade on testnet on Oct. 4, moving the protocol's planned changes into live testing roughly a month before its targeted Nov. 5 mainnet rollout. Block 4,465,026 — the scheduled activation point — was mined at 18:21:45 UTC, according to Zcash testnet block explorer ZecBlock. The project confirmed the activation in a post on X, stating that NU7 was live on testnet.

The upgrade carries three consequential protocol changes. NU7 cuts Zcash's target block spacing from 75 seconds to 25 seconds, a threefold acceleration that compresses confirmation times across the network. It also disables version 4 transactions and integrates a Network Sustainability Mechanism that redirects part of transaction fees into future block rewards, changing the chain's long-term issuance economics.

What does the Sprout deprecation mean for holders?

The most operationally urgent element is the disablement of version 4 transactions. That change leaves ZEC held in Zcash's legacy Sprout shielded pool unspendable unless users move the funds before NU7 fully activates. Users who fail to migrate funds out of Sprout before the mainnet activation height will see those balances frozen on the protocol level, making pre-activation migration the only path to continued access.

The implications extend beyond individual holders. Exchanges, custodians and wallet operators that still support Sprout addresses must complete compatibility work and user notifications before the mainnet height is locked in, or risk holding customer balances that can no longer move.

What happens on Oct. 20?

Zcash developers are scheduled to make a final decision on mainnet activation and set its activation height on Oct. 20, based on how NU7 performs on testnet. The roughly two-week testnet window is deliberately short, intended to surface issues with the faster block cadence and the fee-redirection mechanism under production-like conditions before developers commit to an irreversible mainnet schedule.

The Zcash Foundation said on Friday that testnet operators should use the release candidate to test NU7 "under real conditions." The testnet phase allows developers to assess the upgrade before deciding whether to proceed with mainnet activation, and the Foundation's guidance signals that node operators, miners and block explorers are expected to validate the release candidate rather than wait for final software.

The faster block spacing is the change most likely to stress infrastructure. Third-party services that index the chain, calculate fee estimates or serve shielded transaction pools will need to handle a threefold increase in block frequency. Mining operators and pool software must also adjust to the new cadence before mainnet activation to avoid missed blocks in the first hours after the height is reached.

For Zcash, the Network Sustainability Mechanism represents a structural shift in how the network funds itself once the bulk of issuance flows through fees rather than the original block subsidy schedule. Redirecting part of transaction fees into future block rewards ties long-term security budget to usage, a design question several other proof-of-work chains have deferred.

If testnet performance holds, developers will confirm the mainnet activation height on Oct. 20 and the upgrade will take effect on mainnet on Nov. 5. Sprout holders have until that activation height to move their funds, a deadline that is now roughly one month away.