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Zcash flipped a switch Tuesday. At block 3,428,143, the network activated Ironwood — also called NU6.3 — kicking off what’s probably the most consequential shielded-pool migration in the coin’s history.
The old pool, Orchard, held roughly 3.66 million ZEC at activation. At prices near $463 per coin, that’s about $1.7 billion sitting in a pool that Zcash developers now want everyone to leave behind. The new Ironwood pool started at zero. Every single coin has to be moved manually, by its owner. Nobody can do it for you. And until you move, your ZEC stays in a pool that can’t grow — but also can’t be fully trusted anymore.
The Bug That Started All of This
Here’s the uncomfortable part. Developers found a bug in Orchard’s proof circuit back in May. Not a minor edge case — a flaw serious enough that, if exploited, someone could have minted counterfeit ZEC without leaving any trace on-chain. No footprint. No alarm. Just fake coins slipping into a pool designed to be private by default.
The bug had been sitting there since Orchard launched in May 2022. Three years, basically. Zcash says there’s no evidence anyone actually used it, and that’s reassuring, kind of. But “no evidence of exploitation” in a privacy coin is a tricky claim to make with full confidence — that’s sort of the point of the shielding. The patch came fast once the flaw was found, but it couldn’t retroactively clean up Orchard’s history.
So Ironwood is the answer. Start fresh. New pool, zero balance, and a mechanism designed so that whatever happened before can’t follow the coins through.
How the Turnstile Stops Counterfeit ZEC
The key piece of the migration is something called the turnstile accounting rule. It’s pretty simple in principle: you can only withdraw from the new pool what you can prove you deposited. If you can’t prove it, it doesn’t come out. Counterfeit coins — if any exist — stay trapped in Orchard. They can’t make the jump.
That’s the theory. And it’s a solid one. As of now, 1,500 ZEC have already moved into the new pool. Not a massive number against 3.66 million, but migration just started. The pace from here matters a lot.
Beyond fixing the bug, Ironwood brings two protections that Orchard never had. First, quantum resistance — per ZIP 2005, the new pool’s cryptography is built to hold up even if quantum computers eventually crack current protocols. That’s not a near-term threat for most networks, but Zcash is playing a longer game here. Second, Ironwood’s proof circuit goes through formal verification. That’s a mathematical process that checks the software works correctly under every possible condition, not just the ones developers thought to test. It’s the kind of thing that might have caught the Orchard bug before launch.
ZEC Price and Binance’s Outsized Role
Markets weren’t exactly celebrating. ZEC was trading near $463 ahead of the upgrade but dropped 8% on the day and 15% over the week. It’s still well above where it sat a year ago, so the longer-term holders aren’t panicking — but the short-term move is rough.
Binance is the elephant in the room here. The exchange held about 55% of user funds and accounted for roughly 24% of spot trading volume, even as broader market outflows were happening. That concentration matters for migration speed. If Binance moves its custodied ZEC into Ironwood quickly, the numbers shift fast. If they don’t, the bulk of the supply stays in Orchard for a while longer. Zcash hasn’t said what Binance’s timeline looks like. Unclear.
The migration is voluntary. There’s no deadline forcing anyone’s hand. That’s both a feature and a problem — user-driven transitions tend to drag, especially when the old pool still functions and moving requires deliberate action. The Zcash community will be watching the tracker closely.
And the tracker matters. Right now it shows 1,500 ZEC moved. The remaining 3.66 million is still sitting in a pool that can’t be expanded but also can’t be declared safe. Until that number moves, Zcash’s private supply is basically in limbo.
Binance holds 55% of user funds and hasn’t publicly committed to a migration timeline.
Frequently Asked Questions
What is the Zcash Ironwood upgrade?
Ironwood, also known as NU6.3, activated at block 3,428,143 and retired the Orchard shielded pool, launching a new pool with zero starting balance that includes quantum-resistant cryptography and a formally verified proof circuit.
Why was the Orchard pool retired?
A bug discovered in May in Orchard’s proof circuit could have allowed counterfeit ZEC to be minted without on-chain detection; the flaw existed since Orchard’s May 2022 launch, though no exploitation has been found.
