Zcash Shielded Pools Explained: Sprout, Sapling, Orchard, and Ironwood, and What Happened With the Orchard Bug

Last updated: 30 October 2026

Quick answer

Zcash has had four shielded pools. Sprout (2016) and Sapling (2018) are legacy pools. Orchard (2022) became the dominant pool for shielded ZEC. Ironwood has been the default pool since 28 July 2026, when network upgrade NU6.3 activated at block 3,428,143. Ironwood was introduced after a critical soundness flaw in Orchard’s zero-knowledge circuit, known as the Infinity bug, was discovered in late May 2026. The flaw was patched in early June through emergency measures and the NU6.2 hard fork. Shielded Labs, which disclosed the issue, said it found no evidence that the bug was ever exploited. Ironwood adds a separately tracked pool so that the network can verify the shielded supply as funds leave Orchard. After NU7, expected around 5 November 2026, the Sprout pool is frozen.

What a shielded pool is

Zcash has two kinds of addresses. Transparent addresses work like Bitcoin: the sender, receiver, and amount are visible on the public ledger. Shielded addresses use zero-knowledge proofs: the network can verify that a transaction is valid without seeing who paid whom or how much.

A shielded pool is the set of all value held in shielded notes of one protocol generation. Each pool has its own cryptographic circuit, its own value balance that the network tracks, and its own rules for spending. Funds move between pools through transactions that the network can account for, which is how Zcash keeps the total supply verifiable even though individual shielded balances are hidden.

Timeline of Zcash shielded pools and upgrades

What happened with the Orchard bug

In late May 2026, independent security researcher Taylor Hornby found a critical soundness vulnerability in Orchard’s zero-knowledge circuit during analysis supported by Shielded Labs. A soundness flaw in a proof system means that, in theory, someone could construct a proof the network accepts for a transaction that should be invalid. For a shielded pool, the worst case is counterfeit coins that nobody can see.

The response happened in stages. Developers first disabled Orchard activity through a temporary network patch. On 3 June 2026, the NU6.2 hard fork activated with corrected circuit code and restored the pool. The public disclosure hit the market hard: ZEC fell by about 50%, from roughly $603 to roughly $299, according to crypto.news.

Shielded Labs stated that it found no evidence the vulnerability had been exploited. The limitation of that statement is structural: shielded balances are hidden, so the absence of evidence could not be turned into proof. That is the problem Ironwood was designed to answer.

What Ironwood changes

Ironwood is a new shielded value pool based on Orchard. According to the Ironwood specification, it reuses Orchard’s Action structure and the Halo 2 proof system, so the transition is smaller than introducing a new protocol from first principles. Three things are different:

1. A separately tracked value balance. Funds leaving Orchard pass through an accounting checkpoint before entering Ironwood. Shielded Labs has said this mechanism may produce evidence about whether any counterfeit ZEC was ever created through the Orchard flaw.
2. Quantum-recoverable note plaintexts. New Ironwood notes are created in a format designed to make recovery possible if large quantum computers ever break today’s elliptic-curve cryptography. The specification is explicit that this is not a post-quantum shielded protocol.
3. Transaction version 6. Ironwood bundles travel in a new transaction version.

Ironwood activated on mainnet on 28 July 2026 at block 3,428,143, one week later than the original 21 July target after Shielded Labs raised concerns about ecosystem readiness. Testnet activation came first, on 4 July at block 4,134,000. The upgrade was coordinated across the Zcash Open Development Lab, Shielded Labs, Project Tachyon, and the Zcash Foundation.

For users, the important detail is that existing addresses keep working. Compatible wallets continue to support existing addresses and receiver structures and route new shielded payments to Ironwood automatically. Zodl shipped Ironwood compatibility in version 3.8.0 before activation, with a manual migration option first and a guided in-app migration promised in a later release.

What happens to Sprout and Sapling

NU7, expected around 5 November 2026, makes version 4 transactions invalid. Sprout notes can only be spent through version 4, so the Sprout pool is effectively frozen from that point. Around 22,000 ZEC were still in Sprout in mid-October 2026.

Sapling is not frozen by NU7. Sapling notes can be spent through newer transaction versions. Wallets that can only build version 4 transactions will stop working, however, so legacy software should be replaced before activation.

Why this matters when you receive ZEC

Zcash privacy applies only to shielded funds. If a swap or exchange sends ZEC to a transparent address, that transaction is public, like Bitcoin. Many exchanges support only transparent withdrawals; check the withdrawal page before you request one.

When you receive ZEC from a wallet-to-wallet swap, the address type you provide decides where the coins land. A unified address accepts shielded payments where the sender supports them. A transparent address receives public funds, which some wallets then shield in a follow-up transaction. On SimpleSwap, ZEC is delivered to whatever address you enter, so copy the shielded or unified address from your wallet if that is the outcome you want. Most crypto-to-crypto swaps need no account; the service fee is built into the quoted rate and details are on the website; KYC may be required for transaction security and compliance; availability is subject to the Terms of Service and jurisdictional restrictions. The only official domain is simpleswap.io.

Stefan Lauer, Head of Infrastructure at SimpleSwap, framed the wider point in the CryptoSlate guide on self-custody: “The cypherpunks won the argument about ownership. The least we can do is finish the sentence.” Shielded pools are Zcash’s attempt to finish it, one protocol generation at a time.

Sources

• Zcash Ironwood specification
• Zcash documentation: zcashd end-of-life and NU6.3 timeline
• crypto.news: Zcash confirms July 28 Ironwood activation after Orchard bug
• crypto.news: Zcash sets Ironwood upgrade for July 28 after Orchard bug
• Cointelegraph via TradingView: Zcash targets July 28 launch for Ironwood network upgrade
• Zodl: Zodl 3.8.0, Enabling Ironwood
• Protocol history and governance (Zebra documentation companion)
• CryptoSlate: Self-custody in 2026 (source of the quote)

Related reading

• Zcash NU7 Upgrade on 5 November 2026 
• Monero vs Zcash
• What Is Zcash?
• Zcash on SimpleSwap