Zcash Testnet Begins 25-Second Block Era

Zcash has activated its NU7 upgrade on a public test network, bringing a long-planned change to block production into a live rehearsal environment. The upgrade cuts the targeted block time from 75 seconds to 25 seconds, a threefold increase in block frequency. The activation happened ahead of schedule and gives exchanges, wallet providers, mining pools and developers an opportunity to test software, infrastructure and operational procedures before a planned mainnet rollout on Nov. 5.

The change is not merely a technical tuning exercise. Block time affects confirmation speed, transaction throughput, mining economics, fee markets and the user experience across the Zcash ecosystem. By moving to 25-second blocks on testnet, Zcash developers can observe how the network behaves under real-world conditions, including how quickly transactions propagate, how wallets handle more frequent blocks, and how exchanges update deposit and withdrawal crediting policies.

The NU7 upgrade also includes several economic and privacy-related changes. It redirects 60% of transaction fees to a reserve that will help fund future mining rewards. It reduces per-block rewards to preserve Zcash's issuance schedule. And it disables transactions that use the older Sprout privacy system, a legacy shielded pool that has been superseded by later cryptographic designs.

What NU7 Changes on the Network

NU7 is a network upgrade, meaning it requires coordination across nodes, miners, wallets and service providers. The most visible change is the target block time. Zcash originally launched with a 75-second block interval, a compromise that balanced security, propagation and mining incentives. Moving to 25 seconds means blocks are produced roughly three times as often. That can improve the responsiveness of the chain for users who want faster confirmations, especially for point-of-sale payments, exchange deposits and decentralized applications that rely on timely state updates.

The second major change concerns transaction fees. Under NU7, 60% of fees paid by users will be directed to a reserve. That reserve is intended to support future mining rewards as Zcash's issuance schedule evolves. The remaining 40% continues to flow through the existing fee mechanism. The exact mechanics matter for miners, because fee revenue is a component of mining profitability alongside block subsidies. If fees are redirected, miners may need to rely more heavily on the block reward and on the value of ZEC.

The third change is a reduction in per-block rewards. Because blocks are now produced more frequently, the reward per block must be adjusted downward to preserve the overall issuance schedule. Without that adjustment, Zcash would issue new ZEC faster than planned, altering its scarcity profile and monetary policy. The developers have therefore recalibrated the reward so that the total supply over time remains consistent with the original design.

The fourth change is the disabling of Sprout transactions. Sprout was Zcash's first shielded protocol, launched alongside the network in 2016. It used early zero-knowledge proving technology that has since been improved by Sapling, Orchard and other upgrades. Over time, Sprout has become harder to maintain and less efficient. Disabling it simplifies the codebase, reduces technical debt and removes a legacy privacy system that no longer meets modern performance or security expectations.

Why Block Times Matter for Zcash

Block times are one of the most important parameters in a blockchain network. Shorter block times generally mean faster confirmations, but they also increase the rate at which nodes must validate and propagate blocks. If blocks arrive too quickly, orphan rates can rise, miners may waste work, and network bandwidth requirements can increase. If blocks arrive too slowly, users may wait longer for confirmations, and applications may feel sluggish.

Zcash's move from 75 seconds to 25 seconds places it closer to other high-throughput networks that have experimented with faster block intervals. For a privacy-focused chain, faster blocks can be particularly valuable. Shielded transactions require more computation than transparent transactions, and users often want quick feedback when sending private payments. Exchanges also need to know how many confirmations to require before crediting deposits. A shorter block time can reduce the wall-clock time needed to reach a given confirmation threshold, but it may also require exchanges to reassess their risk models.

Wallet providers face similar questions. A wallet that scans the chain for incoming transactions must handle a higher volume of blocks. Light clients and mobile wallets may need to optimize their sync processes. If a wallet assumes a 75-second average block time, it might poll too infrequently or display misleading confirmation estimates. The testnet phase is designed to surface these issues before mainnet activation.

Fee Redirect and the Future Mining Reserve

The decision to redirect 60% of transaction fees to a reserve is an economic design choice with long-term implications. Miners secure the network by expending computational power, and they are compensated through block subsidies and fees. As Zcash's block subsidy declines over time, fees are expected to become a larger share of miner revenue. Redirecting a portion of fees to a reserve could smooth the transition, create a pool of resources for future mining incentives, or support other network priorities.

However, the mechanism also raises questions. Miners may object if they believe fee revenue is being diverted away from those who provide security. Traders and users may wonder whether fees will rise to compensate for the redirect. Developers will need to communicate clearly about how the reserve is governed, who controls it, and how it will be used. On testnet, these questions can be examined without putting real value at risk.

The reserve also interacts with Zcash's halving schedule and long-term issuance. If block rewards decline and fees are partially redirected, the security budget could become a topic of debate. Some networks have explored tail emissions, fee smoothing or treasury models to address this. NU7 does not solve every long-term funding question, but it introduces a new mechanism that could shape future discussions.

Issuance Schedule and Per-Block Rewards

Zcash, like Bitcoin, has a capped supply and a disinflationary issuance schedule. The exact timing of rewards matters because it affects inflation, miner income and market supply. When block times change, the per-block reward must be adjusted to keep the issuance curve intact. If Zcash produces blocks three times faster but keeps the same reward per block, it would issue ZEC three times faster. That would be a dramatic change to monetary policy and could harm holders.

By reducing the per-block reward, NU7 preserves the intended schedule. Miners will receive smaller rewards per block, but they will find blocks more frequently. In theory, the expected daily reward could remain similar if all else is equal, but variance changes. Smaller, more frequent rewards can be beneficial for smaller miners because they smooth income. Larger miners may need to adjust their accounting and pool payout systems.

Mining pools will also need to update their software. Payout thresholds, fee calculations and share accounting may need to account for the new block cadence. If pools do not upgrade in time, they could experience errors or delays when mainnet activates.

Sprout Shutdown and Legacy Privacy

Sprout was the original shielded protocol for Zcash. It allowed users to send private transactions using zero-knowledge proofs, but it was computationally heavy and required a trusted setup. Later upgrades like Sapling and Orchard improved performance, usability and security. Sprout has remained in the codebase for backward compatibility, but its continued presence creates maintenance burdens and potential risks.

NU7 disables transactions using Sprout. That means holders of funds in Sprout shielded addresses must move them before the upgrade if they want to retain access through the existing system. After the upgrade, Sprout transactions will no longer be accepted. Users who fail to move funds may need to use alternative recovery methods, if available, but the safest path is to migrate before the change goes live on mainnet.

This deprecation is part of a broader trend in privacy-focused cryptocurrencies. Older cryptographic systems are gradually retired as new ones prove faster and more secure. For Zcash, the shift away from Sprout simplifies the protocol and allows developers to focus on newer shielded pools. It also reduces the attack surface, since fewer legacy components remain active.

Mainnet Decision Timeline

Following the public testnet activation, developers will review results and decide on mainnet activation on Oct. 20. If the testnet performs as expected, the mainnet rollout is planned for Nov. 5. That timeline gives exchanges, wallets and other service providers a few weeks to upgrade their software and test their procedures.

The decision point is important because testnet behavior does not always perfectly predict mainnet conditions. Mainnet has real economic value, more users, more miners and more complex infrastructure. A bug that is harmless on testnet could be costly on mainnet. Developers will look for issues such as block propagation delays, orphan rates, node synchronization problems, wallet compatibility failures and mining pool errors.

If problems are found, the mainnet activation could be delayed. If the testnet runs smoothly, the upgrade could proceed as planned. The Oct. 20 decision will therefore be closely watched by the Zcash community.

What Exchanges, Wallets and Developers Are Watching

Exchanges need to update their node software, deposit crediting rules and withdrawal processing systems. A shorter block time may change the number of confirmations required for a given level of security. Some exchanges may keep the same confirmation count, which would reduce waiting times. Others may increase the count to maintain the same risk profile. Either way, exchange operators need to test deposits and withdrawals on testnet before mainnet.

Wallet providers need to ensure they can handle more frequent blocks. Mobile wallets with limited resources may need to optimize their syncing logic. Hardware wallets need to display accurate transaction information. Custodial services need to update their internal ledgers. Developers building on Zcash need to test smart contracts, payment processors and privacy applications under the new block cadence.

Miners and mining pools need to upgrade their nodes and payout systems. They should monitor orphan rates and block propagation times. If 25-second blocks cause too many stale blocks, the network may need to adjust. The testnet phase is the best time to discover such issues.

Background: Zcash and the Privacy Coin Landscape

Zcash launched in 2016 as a privacy-focused cryptocurrency derived from Bitcoin's codebase. It introduced shielded transactions using zero-knowledge proofs, allowing users to hide sender, receiver and amount. Over time, Zcash has evolved through network upgrades that improved cryptography, performance and usability. The project has also faced regulatory scrutiny, exchange delistings and debates about privacy versus compliance.

In recent years, privacy coins have struggled with regulatory pressure. Some exchanges have delisted Zcash and other privacy-focused assets due to compliance concerns. At the same time, demand for privacy tools has persisted, especially among users who value financial confidentiality. Zcash developers have worked to balance privacy with optional transparency, allowing users to choose between shielded and transparent transactions.

NU7 is part of that ongoing evolution. By improving block times, adjusting economics and retiring legacy technology, the upgrade aims to keep Zcash competitive with newer networks. The testnet activation is a milestone, but mainnet rollout will be the real test.

Broader Block Time Race

Zcash's move to 25-second blocks comes as several Layer 1 networks compete on speed. Solana has been working on a 200-millisecond upgrade. Other chains have experimented with sub-second block times. Faster blocks can enable better user experiences, but they also introduce trade-offs in decentralization, hardware requirements and network stability.

For Zcash, the goal is not necessarily to become the fastest chain. Instead, the upgrade aims to modernize the network while preserving its privacy and monetary properties. The 25-second target is a measured improvement, not an extreme change. It gives Zcash a faster confirmation cadence without pushing block times so low that nodes struggle to keep up.

The testnet phase will provide data on how the network performs. If successful, Zcash could join a growing group of chains that have reduced block times to improve usability. If problems emerge, developers can adjust before mainnet.

Risks and Open Questions

There are several risks to watch. First, shorter block times can increase orphan rates. If miners find competing blocks more often, network efficiency may decline. Second, wallets and exchanges may not upgrade in time, causing service disruptions. Third, the fee redirect could create uncertainty for miners and users. Fourth, the Sprout shutdown could strand funds for users who fail to migrate.

There are also open questions about governance and long-term economics. How will the fee reserve be managed? Will it be decentralized? How will decisions about its use be made? These questions may not be fully answered by NU7, but they will shape future upgrades.

For now, the testnet activation is a live rehearsal. Developers will gather data, fix bugs and coordinate with service providers. A final activation decision is expected Oct. 20, with mainnet targeted for Nov. 5.

Source: Coindesk News