Zcash NU7 upgrade cuts block time to 25 seconds, freezes Sprout coins

Zcash switched on its NU7 network upgrade this week, cutting the gap between blocks from 75 seconds to 25 and changing the way the privacy coin pays for its own security.

The network crossed the activation height at block 3,543,405, which The Block reported on November 6. Developers had fixed that block in ZIP 259, the document that defines NU7. Reports differ on whether the chain reached it late on the 5th or in the early hours of the 6th.

Zcash is a cryptocurrency built for private payments. It hides the sender, receiver and amount behind zero-knowledge proofs, a method that proves a transaction is valid without showing what is inside it. Under the hood it tracks coins with unspent transaction outputs, the same bookkeeping Bitcoin uses.

What NU7 changed

NU7 shortens Zcash's target block spacing from 75 seconds to 25, so payments confirm about three times faster. That is the change a user feels. Blocks now land every 25 seconds instead of a little over a minute.

To keep the supply curve intact, the upgrade scales the block reward down by the same factor and triples the number of blocks between each halving. New ZEC still enters at roughly the same rate over time, and the 21 million cap stays in place. Faster blocks, same issuance.

Zcash developer Sean Bowe wrote on GitHub that the height was agreed at a ZIP editor meeting, locking in the target after weeks of testnet trials that began in early October. NU7 also caps how many shielded actions each block and each pool can hold, a guard rail to keep the faster chain stable as more private payments flow through it.

A new way to pay for security

The upgrade also started the Network Sustainability Mechanism, a change to how miners get paid. Under it, 60 percent of the fees in every block are pulled out of circulation and held in a public reserve. Miners keep the other 40 percent. The reserve sits untouched.

Those funds are not gone for good. The plan returns them to miners as extra rewards starting at block 8,939,664, which developers expect to arrive around 2031. Build a buffer now, spend it later, once the regular block subsidy has shrunk.

This problem is real, and not unique to Zcash. Most mining networks pay for their security two ways: new coins minted in each block, and fees from users. The minted part falls on a fixed schedule, halving over the years, so fees have to carry more of the load later on. Bitcoin faces the same arithmetic. Zcash is trying to bank some of today's fees against that future.

Shielded Labs, an independent group that works on Zcash code, called the mechanism its first big deployment on the main network. "Like Bitcoin, Zcash faces a long-term challenge: how to sustain network security as block rewards decline," the group said. Whether a fee reserve answers that, five years before it pays out, is a bet rather than a result.

The coins left stranded

One group of users paid for the switch. NU7 blocks a kind of transaction, called version 4, that was the only way to move funds still sitting in Zcash's oldest privacy pool, known as Sprout. About 12,224 ZEC sat in that pool when the upgrade went live, and under the new rules those coins cannot be spent.

Sprout was the first of several shielded pools Zcash has run. Newer pools replaced it, and the project had been moving activity off Sprout for years. Holders were told, again and again, to move out. Some did not. Blocking version 4 transactions closes that oldest pool for good.

The frozen balance is small next to Zcash's total supply, yet it is a hard reminder that a chain can change the rules under coins nobody touches. ZEC itself has had a loud year. The token traded near $1,255 at about 07:05 UTC on November 6, according to The Block, and it was up more than 148 percent across 2026 by late October, based on CoinGecko figures cited by Cointelegraph. BTC Newz does not publish price forecasts, and a run like that says nothing about the next move.

What to watch

Reliability comes first. Faster blocks raise the chance that two miners find a block at the same moment and one gets thrown away, an event called an orphan. On the testnet, developers said they expect the orphan rate to stay under 1 percent. A testnet is not the live network with real money and real latency. Watch whether that figure holds over the coming weeks.

Second is uptake of the shielded pools NU7 is meant to serve. The Zcash Foundation ran a readiness tracker through the rollout, and support from exchanges and wallets will decide how many people ever see the faster confirmations. A protocol can ship a change. Users still have to adopt it.

Left open: how the reserve performs if fee income stays thin between now and 2031, and whether miners accept a smaller cut today for the promise of more later. Neither question has an answer yet.