Zcash Activates NU7 on Testnet, Cutting Block Times to 25 Seconds

Zcash has switched on its NU7 network upgrade on the public testnet, giving the network its first live run of 25-second blocks ahead of the November 5 mainnet target. The upgrade activated at block height 4,465,026 on October 4, roughly two days before the October 6 estimate the Zcash Foundation set when it shipped the first release candidate.

What NU7 changes

The headline change is block speed. Under ZIP 218, NU7 cuts the target block spacing from 75 seconds to 25 seconds, reducing the average wait for a first confirmation to roughly a third of today’s level. The threefold speedup is aimed at point-of-sale payments, exchange deposits, and cross-chain bridges, where a 75-second wait is a real obstacle. The amount of ZEC issued each day stays the same, so the upgrade leaves the coin’s 21 million supply cap and four-year halving schedule unchanged. NU7 also introduces a Network Sustainability Mechanism: under ZIP 235, 60% of each block’s transaction fees are removed from circulation into a reserve while miners keep the other 40%, and under ZIP 237 each block reissues a small, predictable slice of that reserve on top of its normal reward.

A security budget that outlasts issuance

The reserve is designed to keep paying for network security once block rewards shrink, since rewards halve every four years. The public reserve starts out seeded with the historical funding shortfall from before NU6, giving it a head start. NU7 also tightens shielded transaction limits — 330 Orchard or Ironwood actions and 300 Sapling inputs or outputs per block, with no new Sprout JoinSplits — which more than doubles Orchard throughput while cutting the worst-case sync load a spammer can impose on light wallets by about 37%.

The road to mainnet

The testnet activation is the first time the changes run on a live network, and the Foundation wants operators to upgrade and report issues before a mainnet decision on October 20. Testnet node operators need to upgrade before the activation height to remain on the NU7 chain and help the Foundation test it under real conditions. No mainnet activation height has been set yet, and the release remains a candidate rather than a stable build. If the testnet phase goes smoothly, mainnet activation is targeted for November 5, following the coin-holder vote that backed faster blocks while preserving halvings.