Zcash NU7 Upgrade Speeds Private Payments, Changes Fees and Retires Old Shielding Pool

On Friday, Zcash completed its NU7 network upgrade, which shortens the average interval between blocks from 75 seconds to 25 seconds. The change aims to make shielded (private) payments confirm more quickly and to improve the network’s practical capacity for everyday use.

The upgrade activated at block 3,543,405 (02:34 UTC). Within a few hours the chain produced roughly 225 additional blocks and was averaging about 39 seconds between blocks as difficulty adjusted to the new cadence.

Faster confirmations and user impact

Because Zcash can conceal sender, recipient and amount, faster block times can make shielded transactions more convenient for point-of-sale spending, exchanges and cross-chain transfers. Merchants could see an initial confirmation in about 25 seconds on average, and an exchange that requires three confirmations could shorten its expected wait from nearly four minutes to roughly 75 seconds. Actual wait times remain dependent on each service’s confirmation policy.

Technical changes to maintain miner coordination

Shorter intervals create a narrower window for miners to receive and validate a newly mined block before beginning work on the next one. That compressed timing raises the risk of competing blocks that later get discarded. To address this, the Zcash node implementation Zakura — developed by Valar Group and Project Tachyon — was tested under stressful conditions: 80 machines across 11 regions with every block filled with transactions.

Under that heavy load, the discard (or stale) rate rose to 3.43% at 25-second blocks versus 1.57% at 75-second blocks. Engineers also optimized redundant checks: when a transaction first arrives the node performs its verification and caches parts of that work so the same verifications need not be repeated from scratch once the transaction is included in a block. (Checks that depend on the latest chain state still run again.)

Limits on private activity and capacity estimates

NU7 places limits on how much shielded transaction activity can be included per block. Wallets must scan the blockchain to discover payments addressed to them, and an attacker or heavy user could otherwise force every wallet to perform excessive work. The new limits reduce the worst-case daily download requirement from 271 MB to 169 MB.

Combined with the faster block rate, the specification projects that throughput for simple shielded payments could more than double — from roughly three transactions per second to over six.

Fee allocation and supply mechanics

Fee rules were adjusted by NU7: miners now receive 40% of transaction fees, while 60% of each fee is removed from circulation and tracked in a reserve. That reserve is scheduled to start supplementing block rewards around February 2031. The mechanism is designed to preserve Zcash’s 21 million coin supply cap.

Retirement of Sprout and unspendable funds

The upgrade also retired Sprout, Zcash’s original shielded pool dating to 2016. As a result, roughly 12,224 ZEC in Sprout-based notes are currently unspendable. Co-founder Sean Bowe has proposed potential recovery approaches, but as of the upgrade’s activation none have been formally approved.

Note: The network’s parameters and client implementations will continue to evolve; services and wallet providers may set different confirmation or scanning policies that affect end-user experience.