Zcash activates Ironwood upgrade, retires Orchard to exit-only after shielded pool flaw

Activation and migration

According to Project Tachyon and the Zcash development team, Ironwood launched on schedule and Orchard has now been placed into an exit-only mode. That means users can withdraw funds from Orchard, but the older pool no longer accepts new shielded activity.

Migration has already started. Data cited from Zcash’s migration tracker shows about 40,207 ZEC have moved into Ironwood so far, while roughly 3.6 million ZEC remain in Orchard awaiting migration.

The upgrade follows months of work by several Zcash-related organizations after researchers disclosed what became known as the Orchard “infinity” bug. Developers said the issue could theoretically have allowed counterfeit ZEC to be created without public detection, though they also said they found no evidence that the flaw had been exploited.

Why Orchard was replaced

Shielded Labs said researcher Taylor Hornby discovered the bug in late May in Orchard’s zero-knowledge circuit. Emergency changes in early June temporarily disabled Orchard, and corrected circuit code was later deployed through the NU6.2 hard fork.

Even after that patch, developers said Zcash’s privacy design meant it was not possible to prove with certainty that hidden inflation had never occurred. That limitation led the ecosystem to pursue a replacement pool rather than continue relying only on a patched version of Orchard.

Ironwood introduces a separate accounting boundary, with its own note commitment tree, nullifier set and chain value pool. Project documentation says this allows nodes to track the new shielded pool independently from Orchard.

The upgrade also adds a public accounting checkpoint, described as a turnstile, that allows funds to leave Orchard while preventing more value from exiting the old pool than was legitimately entered into it. Developers have said the mechanism is meant to trap any hypothetical counterfeit coins inside Orchard while preserving independent checks on whether Zcash’s circulating supply stays within its 21 million ZEC issuance limit.

Formal proof and security claims

Alongside activation, Project Tachyon said researchers completed a machine-checked mathematical proof for Ironwood’s balance integrity. According to the group, that proof supports the claim that Ironwood cannot create undetectable counterfeit ZEC under its stated cryptographic assumptions.

Project Tachyon said the proof was written in Lean and includes more than 2,700 theorems developed over more than a month by three teams of researchers and cryptographers. The work is said to verify the parts of the system needed for balance integrity, including the zero-knowledge proof system, circuit rules and ledger-level accounting. Researchers also said the verification does not cover Ironwood’s separate privacy guarantees.

Ironwood also includes ZIP 2005 quantum-recoverable notes. According to the ZIP specification, the feature could support a future recovery mechanism if quantum computing weakens current cryptography, but it does not make current Zcash transactions quantum secure on its own.

Ecosystem rollout and market reaction

The replacement effort involved Shielded Labs, the Zcash Open Development Lab, Project Tachyon, Valar Group and the Zcash Foundation. Shielded Labs, co-founded by Zcash founder Zooko Wilcox, had proposed replacing Orchard after the vulnerability became public.

ZODL Executive Director Josh Swihart said on X that his organization’s engineers contributed 82% of the merged changes across protocol and wallet repositories during the effort. He also said Orchard was patched within five days and that the replacement was completed in about 60 days.

The NU6.3 upgrade also finalizes a separate transition in node software. According to the Zcash Foundation, the older zcashd software no longer supports the new consensus rules, making Zebra the required node implementation after activation. Before launch, Shielded Labs Executive Director Jason McGee had said exchanges, wallet providers and mining pools were preparing both for Ironwood and for migration from zcashd to the Z3 software stack, and that some operators needed more time, though the upgrade was not delayed.

ZEC briefly fell around 9% to about $460 after the upgrade before recovering to roughly $475. The token had already seen heavy volatility after the Orchard issue became public, falling by more than half before later rebounding from about $45 in September last year to nearly $700 by year-end.

With Ironwood now live, the immediate focus for the network is the gradual transfer of remaining shielded funds out of Orchard through the new turnstile model, while the older pool is phased out under the new accounting structure.