Zcash developers have proposed cutting the network’s target block spacing from 25 seconds to 20, and want the change in the next community poll and in the NU7.1 upgrade. The proposal was posted on the Zcash Community Forum at 20:56 UTC on 8 Nov by developer ValarDragon, who says it was co-written with Evan Forbes.

Zcash is a so-called privacy coin, a blockchain whose shielded pools can hide amounts and addresses. Block spacing is the average time between blocks, and every transaction waits for one before its first confirmation. NU7 went live last week and moved blocks to 25 seconds from 75.

The authors call this a follow-on to ZIP 218, the 25-second change, and describe it as “latency-only”. They argue faster confirmations help point-of-sale payments, exchange deposits and cross-chain swaps where a counterparty needs one confirmation before acting.

What would change

The block-time cut is the main edit, but the draft rewrites several other numbers to hold wall-clock behaviour steady, according to the post:

  • Shielded action limits per block would be scaled by 4/5, so the global budget and the Orchard and Ironwood limits would each fall from 330 to 264, and Sapling inputs plus outputs from 300 to 240. Daily shielded capacity would stay the same.
  • Each block’s subsidy would also be scaled by 4/5, and the halving interval would move from 5,040,000 to 6,300,000 blocks, so daily issuance stays unchanged.
  • Default transaction expiry would grow from 120 to 150 blocks, and the difficulty averaging window from 102 to 128 blocks.
  • The 2 MB block size limit would stay.

The main risk is orphan blocks, which are valid blocks that lose a race and are discarded. The authors tested an 80-miner network spread over 12 regions with full 2 MB blocks and report orphan rates of 1.9% with a Zakura-only network and 3.3% with a 50-50 mix of Zakura and Zebra-Andele nodes. They say the earlier 25-second proposal was judged safe at 4.68% in an empirical test and 3.26% in a theoretical model.

These are the proposers’ own figures, and they are test-network results, not mainnet data. ValarDragon also says the live orphan rate is lower than before NU7.

Replies so far are few. One asks whether 20 seconds is the true optimum and not, say, 17 or 21.4. Another argues for a different consensus design altogether. ValarDragon answered that block-time cuts do not compete with future latency work, and put peak bandwidth at about 80 KB/s now and 100 KB/s under the change.

The height for the first cut, 25 seconds, was set in October. We found no poll date and no date for NU7.1.

ZEC traded at $1,229.53 on Kraken at 14:51 UTC. The next milestone is the community poll, for which no date has been set.

This article is for information only and is not investment advice.