Short answer: On July 28, 2026, Zcash activated the Ironwood upgrade (NU6.3) at block 3,428,143, opening a new shielded pool and turning the old Orchard pool, which held about 3.6 million ZEC (roughly $1.7 billion), into a withdraw-only pool. The Zcash Ironwood upgrade is the network's answer to a four-year-old Orchard bug that could have allowed counterfeit ZEC to be minted without a trace.
What happened
Zcash (ZEC), the privacy-focused cryptocurrency built on zero-knowledge proofs, completed its NU6.3 network upgrade on Tuesday, July 28, 2026. From that block onward, the Orchard shielded pool no longer accepts new deposits or internal transfers. Holders can only move coins out of it, and the natural destination is a new shielded pool, also called Ironwood, which started the day empty.
- Size of the sealed pool: about 3.6–3.7 million ZEC, worth around $1.7 billion at the time. At its peak Orchard held close to 88% of all shielded ZEC.
- Early migration: within the first hours only a small share had moved; The Block counted about 40,000 ZEC in Ironwood.
- Price: ZEC fell about 9% to near $460 on the day before recovering toward $475.
- Who built it: contributors included ZODL, Project Tachyon, Valar Group, the Zcash Foundation and Shielded Labs.
What the Orchard counterfeiting bug was
Orchard went live in May 2022 as Zcash's most modern shielded pool. In late May 2026, Shielded Labs researcher Taylor Hornby found a flaw in its zero-knowledge circuit that could, in theory, let an attacker create ZEC out of nothing. Because shielded balances are private by design, such coins would have been indistinguishable from real ones.
Developers shipped emergency fixes in June, including the NU6.2 hard fork that temporarily disabled Orchard and corrected the circuit. No evidence of exploitation has been found — Orchard's balance grew steadily over the whole period — but privacy made it impossible to prove a negative. ZEC dropped sharply on the disclosure, losing more than a third of its value, before recovering as the Ironwood plan took shape.
How the Ironwood turnstile protects ZEC supply
Ironwood does not try to find counterfeit coins inside Orchard, which cannot be done. Instead it contains them. A "turnstile" is an accounting rule at the boundary of a shielded pool: total withdrawals can never exceed the total that was verifiably deposited. If someone did mint fake ZEC in Orchard, the pool would run dry before those coins could all leave, so they would stay trapped rather than dilute the rest of the supply.
| Feature | Orchard (2022–2026) | Ironwood (from July 28, 2026) |
|---|---|---|
| Status | Withdraw-only | Active shielded pool |
| Circuit assurance | Flaw went unnoticed for four years | Formally verified proofs |
| Supply protection | Turnstile caps exits at verified deposits | Separate note tree and nullifier set |
| Quantum readiness | None | Quantum-recoverable notes (ZIP 2005) |
Two further changes look ahead. Ironwood's proof circuits are formally verified, meaning a machine-checked proof shows they behave as specified. Its notes are also designed to be recoverable if quantum computers ever break today's elliptic-curve cryptography, following specification ZIP 2005.
What changes for Zcash users, wallets and exchanges
- Shielded holders move funds themselves. Coins in Orchard stay yours; you simply have to send them through the turnstile into Ironwood using an updated wallet.
- There is no need to rush. Developers advised against moving everything at once and suggested routing wallet traffic through Tor or a VPN, because a sudden transfer can link your IP address to a balance.
- Node operators must run Zebra. The older zcashd software does not support the new consensus rules.
- Transparent ZEC is unaffected. Coins on t-addresses, and the older Sapling and Sprout pools, work as before.
What it means for you
If you hold ZEC on an exchange or on a transparent address, you do not need to act. If you use a shielded wallet, update it before doing anything, confirm it supports Ironwood, and migrate in parts rather than in a single transaction. Be wary of "migration helpers" or support accounts offering to move coins for you — no legitimate upgrade needs your seed phrase. Our wallet security guide covers the basics.
If you swap ZEC, expect some services to pause shielded deposits while they upgrade, and check which address type a service supports before sending. The episode is also a reminder that privacy coins carry a particular kind of risk: when balances are hidden, a supply bug is harder to rule out.
Key takeaways
- Zcash activated Ironwood (NU6.3) on July 28, 2026, at block 3,428,143.
- The Orchard pool, with about 3.6 million ZEC (~$1.7 billion), is now withdraw-only.
- A turnstile keeps any counterfeit ZEC trapped; no exploitation has been found.
- Ironwood adds formally verified circuits and quantum-recoverable notes.
- Shielded holders need an updated wallet to migrate; transparent holders need do nothing.
For background on how shielded coins differ from transparent ones, read our explainer on privacy coins, and see the list of supported coins before planning a swap.
Sources: CoinDesk, The Block, Decrypt, crypto.news
Frequently asked questions
Do I need to move my ZEC after the Ironwood upgrade?
Only if your ZEC sits in the Orchard shielded pool. Those coins remain yours but can only be withdrawn, so move them to Ironwood with an updated wallet; coins on exchanges or transparent addresses need no action.
Was the Zcash Orchard bug exploited?
No evidence of exploitation has been found, and Orchard's balance grew steadily while the flaw existed. Because shielded balances are private, this cannot be proven outright, which is why Ironwood adds a turnstile to trap any counterfeit coins.
What is a turnstile in Zcash?
A turnstile is an accounting rule that caps the total amount leaving a shielded pool at the total verifiably deposited into it. It stops counterfeit coins, if any exist, from entering circulation.
