Zcash developers announced the launch of the NU7 mainnet, scheduled for Nov. 5, and the testnet activation for Oct. 6, following the decision by the ecosystem engineering teams to deploy, in addition to NU5 in NU6, 25-second blocks, the disabling of version 4 transactions, and the Network Sustainability Mechanism. A final decision will be made on the mainnet start date on Oct. 20.
Per Sean Bowe’s statement, there is a shared understanding between Zcash Foundation, Project Tachyon, Valar Group, ZODL, Shielded Labs, and all engineers about the scope and timeline of the deliverables, which will be ready by Sept. 30. Afterward, engineers will deploy NU7 to a testnet and observe its behavior over a two-week period before setting a new mainnet activation height.
One of NU7’s major proposals is ZIP 218, lowering Zcash’s target block time from 75 seconds to 25 seconds (tripling block rate) while continuing to issue the same number of ZEC each day by reducing the subsidy paid per block. ZIP 218 seeks to decrease confirmation times for payments, deposits at exchanges, and cross-chain operations (interoperability with other blockchains).
The proposal defines maximum actions to limit the cost of running the network per block. A block may not contain more than 330 total actions across all pools, including at most 330 Orchard actions, 300 Sapling inputs and outputs combined, and 25 Sprout JoinSplits. The expected throughput in the number of standard two-action transactions per second in Orchard is 2.9, and before and after optimization, 6.6.
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Tests showed that ZIP 218 had a theoretical stale block rate of around 3.26% when the inter-block spacing was 25 seconds. Testing from a global region with 99 Zebra nodes using 2 MB blocks showed a stale-rate of 4.86% and fork-rate of 0.37%.
Shielded wallets’ worst-case required bandwidth for initial sync has been estimated to drop from 271 megabytes (MB) to 169 MB per day with the faster block schedule, but more work to sync full nodes will be done per unit time: considerably more blocks will have to be processed in the same amount of time. Developers monitoring testnet performance prior to activation will consider this.
NU7 is also expected to deactivate version 4 transactions, so that it would not be possible to spend from the legacy Sprout pool with version 5 transactions, for example. The remaining balance of coins in the Sprout pool would not move to the orphaned state and could potentially be salvaged with a future recovery mechanism, though none is currently planned.
The planned Network Sustainability Mechanism would keep Zcash’s halving schedule in the next inflationary period, as decided in the most recent governance vote. Under the selected proposal, at least 60% of transaction fees would be burned and re-injected into the circulating supply around February 2031.
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The schedule is not final; developers can drop any feature they are working on that does not make the Sept. 30 deadline. Within Zcash ZIP repository, many major proposals for the NU7 are labeled as draft or candidate, with the hope that the review on Oct. 20 will decide whether to test and activate them at the Nov. 5 mainnet height.
