Zcash Developers Propose 20-Second Blocks After NU7 Speeds Confirmations

Zcash developers Dev Ojha and Evan Forbes proposed cutting the network's target block time from 25 seconds to 20 seconds on Nov. 8, two days after the NU7 upgrade tripled block production speed at block 3,543,405.

The proposal, published on the Zcash community forum, asks for the change to be considered in the follow-up NU7.1 upgrade. It has not received community approval, and no activation date exists.

What did NU7 change?

Zcash activated NU7 on Nov. 6, reducing the interval between blocks from 75 seconds to 25 seconds without altering the 21 million ZEC maximum supply. The upgrade introduced new shielded transaction limits and a fee system that reserves 60% of transaction fees for future mining rewards, paying miners the remaining 40% directly.

The new proposal would cut the expected wait for a first confirmation from 25 seconds to roughly 20 seconds. An exchange requiring three confirmations would see its target waiting period fall from 75 seconds to 60 seconds. The developers identified retail payments, exchange deposits and cross-chain swaps as activities that would benefit. Actual times vary, because miners do not find blocks at fixed intervals and service providers set their own confirmation thresholds.

Do mining data support faster blocks?

The central risk of shorter intervals is more orphaned blocks — competing blocks that miners discard without reward. Data from ZecBlock's mining tracker showed an observed orphan rate of 0.69% over the 24 hours ending early Monday, against approximately 0.66% before NU7. The rate across the entire post-upgrade period measured 1.29%, reflecting an initial rise that later declined.

"The orphan rate has gotten better than I anticipated!" Ojha, known as ValarDragon, wrote in a Monday update. ZecBlock expanded its observation network from one node to ten shortly before the upgrade, so the earlier and current figures are not directly comparable.

Developers also ran simulations with 80 miners distributed across 12 geographic regions. Those tests produced orphan rates between 1.9% and 3.3% depending on mining software configuration, compared with 4.68% in earlier tests that assessed the safety of 25-second blocks.

How would capacity and issuance change?

The draft technical plan would not raise the network's daily shielded transaction capacity. It would cut the maximum number of shielded actions per block from 330 to 264 and keep the 2 MB block size limit unchanged. Developers explained that keeping per-block limits constant while producing more blocks would increase the data wallets must download and process.

The proposal would adjust the block subsidy and halving interval to preserve Zcash's existing issuance schedule. It would retain the recommended confirmation anchor depth of three blocks while extending the default transaction expiry from 120 blocks to 150 blocks, preserving the same expected expiry period.

In a Nov. 9 post, Ojha explained that NU7 raised the difficulty averaging window from 17 blocks to 102; the 20-second interval would raise it to 128. He estimated difficulty fluctuations that previously ranged from roughly -40% to +30% could narrow to between -20% and +15%, though actual performance remains unobserved.

What happens next?

Ojha and Forbes want the proposal included in the next Zcash community poll and considered for NU7.1. The earlier NU7 rollout required node operators to update their software for the new consensus rules, and any adopted interval change would follow the same activation process. A community poll on the 20-second block interval is the next decision point before NU7.1's scope is finalized.