Zcash Network Upgrades: A Complete Timeline

Zcash has activated ten major network upgrades since its 2016 launch, with an eleventh (NU7) proposed and pending, each activating automatically at a specific block height once the network adopts it. This page is a reference to what each one actually changed — not the story of the project (see The History of Zcash for that), just the upgrades themselves, in order.

What a Zcash network upgrade actually is

A network upgrade is a coordinated, scheduled change to Zcash's consensus rules that every full node and miner must adopt at the same block height, or fall onto a separate legacy chain. ZIP 200 defines the mechanism: each upgrade gets an activation height, decided well in advance so node operators have time to update their software, plus built-in replay protection so a transaction valid on one side of the upgrade can't be replayed on the other. A single network upgrade is often a bundle of several ZIPs (Zcash Improvement Proposals) activated together — see Who Runs Zcash? for how a ZIP actually gets from proposal to activated upgrade.

The timeline at a glance

October 2016 — Launch, with the original Sprout shielded pool
June 2018 — Overwinter — groundwork for future upgrades
October 2018 — Sapling — dramatically faster shielded transactions
December 2019 — Blossom — 75-second blocks (a rate change, not a halving)
July 2020 — Heartwood — private mining rewards, light-client support
November 2020 — Canopy — first halving, new development fund
May 2022 — NU5 — Orchard shielded pool, Unified Addresses
November 2024 — NU6 — second halving, funding model overhaul
November 2025 — NU6.1 — coinholder-directed funding, technical fixes
June 2026 — NU6.2 — emergency fix for a critical Orchard vulnerability
July 2026 — NU6.3 (Ironwood) — new shielded pool, current Mainnet rules
Proposed, not active — NU7 — 25-second blocks, subsidy re-denomination

Launch — Sprout (October 2016)

Zcash launched on October 28, 2016 with its original shielded pool, Sprout — the first production use of zk-SNARKs in a live cryptocurrency. There was no on-chain upgrade mechanism yet; that came with Overwinter two years later. Sprout's proving system was slow (proof generation could take over a minute) and required a one-time "trusted setup" ceremony, both problems later upgrades solved.

Overwinter (June 2018)

Activated June 26, 2018, at block height 347,500. Overwinter didn't change what Zcash could do — it changed how future upgrades would work. It introduced transaction versioning, two-way replay protection between consensus branches, and transaction expiry, laying the technical groundwork the network upgrade mechanism (ZIP 200) still relies on today.

Sapling (October 2018)

Activated October 29, 2018, at block height 419,200. Sapling replaced Sprout's proving system with a faster one (Groth16) and a redesigned circuit, cutting shielded transaction proof time from minutes to seconds — the upgrade that made shielded transactions practical on mobile phones for the first time. See How Zcash Works for the cryptography in more depth, or the Zcash privacy hub for how this fits into Zcash's privacy model overall.

Blossom (December 2019)

Activated December 11, 2019, at block height 653,600. Blossom cut Zcash's target block spacing from 150 seconds to 75 seconds and, in the same upgrade, cut the block subsidy from 12.5 to 6.25 ZEC to match — keeping total ZEC issued per unit of real time unchanged. This was a rate change, not a halving; Zcash's first official halving came a year later, with Canopy. For the full mechanics of how block-time changes and subsidy cuts relate (including the pending NU7 upgrade, which does the same kind of thing again), see Zcash Halving Explained.

Heartwood (July 2020)

Activated July 16, 2020, at block height 903,000. Heartwood shipped two changes: Shielded Coinbase, letting miners send block rewards directly to a shielded address instead of a public one, and FlyClient, a more efficient verification method for lightweight clients. See How Zcash Mining Works for what miners actually do with each block.

Canopy (November 2020)

Activated November 18, 2020, at block height 1,046,400. Canopy paired two changes: Zcash's first official halving (block subsidy 6.25 → 3.125 ZEC) and the end of the original Founders' Reward, replaced by a new on-chain development fund. It's the point where funding Zcash's development stopped being fixed at launch and became something the protocol itself would keep adjusting through later upgrades.

NU5 — Orchard (May 2022)

Activated May 31, 2022, at block height 1,687,104. NU5 introduced Orchard, a new shielded pool built on the Halo 2 proving system — the first Zcash shielded pool that needs no trusted setup ceremony at all — alongside Unified Addresses, which bundle transparent and shielded receivers into one address. This is also where Zcash's public naming shifted from codenames (Sapling, Canopy) to sequential numbers.

NU6 (November 2024)

Activated November 23, 2024, at block height 2,726,400. NU6 paired Zcash's second halving (block subsidy 3.125 → 1.5625 ZEC) with a full overhaul of the development-fund model: the old arrangement, which sent a fixed 20% split directly to Zcash Community Grants, Electric Coin Company and the Zcash Foundation, ended. In its place, 80% of each block's subsidy goes to miners and 12% accrues in a protocol-tracked "lockbox," undirected until the community decides what to do with it — alongside a smaller consensus change requiring the full subsidy and fees to be collected in coinbase transactions.

NU6.1 (November 2025)

Activated November 24, 2025 at 19:56 UTC, at block height 3,146,400. NU6.1 put the NU6 lockbox to work: the accrued funds became a coinholder-directed fund under a "Community and Coinholder" model, giving ZEC holders a direct say in larger grants rather than leaving everything to accrue indefinitely. It also shipped smaller technical fixes — correcting how wallet RPC methods report Orchard unshielding, and switching the default transaction format to the more extensible version introduced with NU5.

NU6.2 (June 2026)

Activated at block height 3,364,600, around June 3, 2026. NU6.2 was an emergency response, not a planned feature upgrade. In late May 2026, an independent security researcher privately disclosed a critical flaw in the Orchard shielded pool's zero-knowledge proof circuit — one that could, in principle, have allowed double-spending inside the shielded pool. The network responded in two steps: a temporary soft fork at block 3,363,426 (around June 2) disabled new Orchard transactions entirely while a fix was prepared, followed by the NU6.2 hard fork a day later, which corrected the proof-verification logic and re-enabled Orchard. Investigators found no evidence the flaw had actually been exploited — the network's supply-conservation checks showed no unauthorized ZEC had been created — but the shielded pool's own privacy guarantees meant that absence of evidence couldn't be fully proven the way it could for a transparent chain. That residual uncertainty is what NU6.3, a month and a half later, was built to close.

NU6.3 — Ironwood (July 2026)

Activated July 28, 2026, at block height 3,428,143. Ironwood is Zcash's response to the NU6.2 incident: rather than patching Orchard again, it introduces an entirely new shielded pool, built with formally verified proof circuits, and restricts Orchard to withdrawals only — no new deposits or internal transfers are permitted into or within Orchard anymore. Existing shielded value moves forward into Ironwood through Zcash's existing turnstile mechanism as holders and wallets migrate. Ironwood is designed to give users a way to independently verify the shielded pool's supply integrity going forward, closing the kind of uncertainty NU6.2 could only contain. The upgrade also marked the end of official support for zcashd, the original node software — full nodes need Zebra going forward.

Where things stand today (September 2026)

Right now, on Mainnet, Zcash runs under NU6.3 (Ironwood)'s consensus rules: roughly 75-second blocks, a 1.5625 ZEC block subsidy, the Community and Coinholder funding model, and the Ironwood shielded pool as the destination for new shielded activity. Nothing below this point has activated yet.

NU7 — proposed, not active

Zcash token holders voted in September 2026, with roughly 99.9% support, in favor of ZIP 218, which would activate as part of NU7: cutting target block time from 75 to 25 seconds and re-denominating the block subsidy to match, without changing Zcash's underlying issuance schedule. As of publishing, NU7 hasn't activated — code is due to be finalized before September 30, testnet activation is planned for October 6, and a final go/no-go decision on the tentative November 5, 2026 mainnet target is expected around October 20. That date is a target, not a guarantee. For the full subsidy mechanics — including why 25-second blocks don't mean three times the ZEC issuance — see Zcash Halving Explained and How Zcash Mining Works.

FAQ

How many network upgrades has Zcash had? Ten activated so far: Overwinter, Sapling, Blossom, Heartwood, Canopy, NU5, NU6, NU6.1, NU6.2, and NU6.3 (Ironwood). Zcash's 2016 launch itself, with the original Sprout shielded pool, predates the network-upgrade mechanism. NU7 is proposed but not active as of September 2026.

What was Zcash's first network upgrade? Overwinter, activated June 26, 2018 at block height 347,500. It didn't add user-facing features — it built the replay-protection and versioning mechanism later upgrades rely on.

Which Zcash upgrade introduced Orchard? NU5, activated May 31, 2022 at block height 1,687,104. It's also where Zcash shifted from codenamed upgrades to sequential numbering.

Was Blossom a Zcash halving? No. Blossom (December 2019) cut the block subsidy in half, but only because it also cut block time in half — it was a rate change, not an official halving. Zcash's first official halving was Canopy, a year later.

What's the difference between NU6 and NU6.1? NU6 (November 2024) paired the second halving with creating a protocol-tracked "lockbox" for undirected development funds. NU6.1 (November 2025), a year later, turned that lockbox into an active coinholder-directed funding mechanism, plus some unrelated technical fixes.

Was there a Zcash security incident in 2026? Yes. In May 2026, a critical vulnerability was privately disclosed in the Orchard shielded pool's proof circuit. Zcash responded with an emergency soft fork, then the NU6.2 hard fork days later to fix it. No evidence of actual exploitation was found. NU6.3 (Ironwood), in July 2026, followed up with a newly built shielded pool as the longer-term fix.

What is Zcash's current network upgrade? As of September 2026, Zcash runs under NU6.3 (Ironwood), activated July 28, 2026. NU7 is the next proposed upgrade, not yet active.