Zcash activates 25-second blocks on public testnet early

Zcash activated its NU7 upgrade on public testnet on Oct. 4, moving the target time between blocks from 75 seconds to 25 and starting the live trial two days before the Zcash Foundation’s estimate. The change could cut the average wait for a first confirmation, but for now it applies only to test coins. The Foundation’s Zebra 7.0.0-rc.0 announcement had put activation at block 4,465,026 around Oct. 6; CoinDesk reports the testnet reached that block on Oct. 4.

What changes with 25-second blocks?

NU7 targets three blocks in the time Zcash previously targeted one. According to the CoinDesk report on the activation, that would bring the average wait for a first confirmation down from 75 seconds to 25 if the target is met. Block times vary, and a shorter target does not guarantee that a merchant or exchange will accept a payment sooner: services set their own confirmation requirements. A service that waits for three confirmations, for example, would still be targeting about 75 seconds under NU7, compared with 225 seconds at the old interval.

More frequent blocks also mean more blocks are produced over the same period, so the reward per block falls to one-third to preserve the existing ZEC issuance schedule. The Foundation says the daily amount issued and the 21 million ZEC supply cap remain unchanged. That distinction matters: the upgrade changes how often rewards are distributed, not the planned pace of new coin issuance.

What else is being tested before mainnet?

NU7 changes how transaction fees contribute to future miner rewards. The Foundation says miners keep 40% of each block’s transaction fees, while 60% goes to a reserve that can fund rewards later. That reserve is intended to help support network security as block rewards decline through halvings. It is a change to the fee flow, not an increase in current ZEC issuance.

The upgrade also sets per-block limits for shielded transactions. The Foundation’s release notes specify a shared limit of 330 actions across pools, with separate limits for Orchard or Ironwood and Sapling, and no new Sprout JoinSplits. Those rules are intended to add shielded capacity while limiting the verification load that spam could impose on lightweight wallets. The changes give wallet and infrastructure operators more to assess than block timing alone.

The public testnet is the rehearsal before any production change. CoinDesk reports that both major node programs support the trial, while the Foundation says its Zebra release is a release candidate and that mainnet operators do not need to upgrade yet. The test gives developers and operators a place to check the new consensus rules across miners, wallets and node software before they affect real ZEC.

When could NU7 reach Zcash mainnet?

Nov. 5 is a planned target, not a confirmed activation date. Developers expect to review test results on Oct. 20 and decide whether to proceed; CoinDesk reports that no mainnet activation block has been set. That leaves the schedule dependent on what the public trial shows. The next signals to watch are whether testnet operators report problems, whether the Oct. 20 review sets a mainnet height, and whether the planned November target holds.

Sources and documents

• Zebra 7.0.0-rc.0 announcement — forum.zcashcommunity.com
• CoinDesk report on the activation — coindesk.com