Tachyon (Zcash)

On April 2, 2025, Zcash cofounder Sean Bowe published “Tachyon: Scaling Zcash with Oblivious Synchronization” on his blog, proposing a set of changes to scale the Zcash protocol incrementally while giving existing users and wallets a smooth transition. He argued that zk-SNARK verification had never been the barrier to scaling Zcash; the real bottleneck is that shielded transactions must be indistinguishable from one another, which requires communicating and coordinating global state. The key is a new model for how wallets interact with the blockchain that he calls “oblivious synchronization,” together with proof-carrying data (PCD) to keep blocks small and fast to verify no matter how many shielded transactions they contain.⁠[1][1][1][1][1]

The plan also assumes that future payments will have senders and recipients exchange payment information through an out-of-band channel, removing on-chain ciphertexts entirely; Bowe acknowledged the costs, such as users no longer being able to recover funds from the blockchain using only a seed phrase or to post a payment address publicly, which would require additional infrastructure. He said the plan could be deployed in the short term with cryptography Zcash already knows how to deploy, without relying on speculative research, in an engineering effort comparable to the earlier Sapling upgrade.⁠[1][1][1][1][1][1]

On April 17, 2025, Bowe introduced Ragu, a Rust recursive-proof (PCD) toolkit he was building for Tachyon, which supports non-uniform circuits, uses a simple R1CS-like arithmetization and is built specifically for the Pasta curves used by Orchard. On May 15, he explained that Tachyon would fully embrace out-of-band payments for the first time in a Zcash shielded protocol, removing in-band secret distribution and with it key diversification, viewing keys and even payment addresses, while keeping parts of Orchard’s design; Tachyon could be deployed either as an upgrade to the existing Orchard pool or, using a turnstile, as a standalone shielded pool.⁠[2][2][2][3][3][3][3]

On October 16, 2025, Bowe wrote that, as part of the Tachyon scaling work, in-band secret distribution would be removed from Tachyon transactions to fully defend against quantum attacks on the privacy of on-chain transactions, addressing “harvest now, decrypt later” threats.⁠[4][4]

That month, a member of the Zcash Community Forum argued that Tachyon had too many downsides, lacked a proof of concept and benchmarks, and should not be prioritized over Crosslink; Shielded LabsShielded LabsShielded Labs is a nonprofit Zcash support organization based in Switzerland, established as a Swiss association in December 2022. It operates mainly on donations and has never received Zcash Development Fund money or block rewards. It leads protocol proposals including the Network Sustainability Mechanism (NSM) and Crosslink, a hybrid proof-of-work and proof-of-stake consensus, and after a researcher it engaged discovered the Orchard counterfeiting vulnerability in 2026, it proposed and advanced the Ironwood upgrade together with other development teams.Open the full entry Engineering Manager Mark Henderson clarified that Crosslink and Tachyon are separate efforts whose roadmaps and timelines do not necessarily affect each other.⁠[5][5][5][5]

In February 2026, Project Tachyon opened its X account, @TachyonZcash. On March 17, Bowe presented Tachyon at Zcash Engineering Office Hours #5. The organizers explained that existing Zcash wallets must scan every encrypted transaction on the chain to find their funds and that validators must permanently store an ever-growing nullifier set, making it impossible for Zcash to scale to billions of users; Tachyon introduces recursive PCD and oblivious synchronization so that wallets can stay current without downloading the whole chain or revealing what they are looking for, paving the way to thousands of shielded transactions per second.⁠[6][7][7][7][7][7]

On May 7, 2026, Bowe and Tal Derei described Ragu’s design: it aims to be a production-grade realization of the original Halo paper and, in the spirit of risk aversion, relies heavily on tools Zcash already deployed in Orchard — the Pasta elliptic curve cycle, the Poseidon hash and polynomial commitments based on inner product arguments — largely avoiding cryptography newer than 2021; unlike the hand-optimized PLONK-style arithmetization used for Orchard in the halo2 library, Ragu uses a simple R1CS-like recipe.⁠[8][8][8][8]

After the Orchard counterfeiting vulnerability was found in May 2026, Project Tachyon paused its own roadmap. On June 6, it proposed the Ironwood upgrade in a joint statement with Valar GroupValar GroupValar Group is a cryptography research and engineering team focused on developing the Zcash protocol, led by Osmosis co-founder Dev Ojha and staffed largely by engineers from Osmosis and Celestia; in 2026 it took part in the Ironwood network upgrade, released the full-node software Zakura with Project Tachyon, and built Zcash’s private coinholder voting chain.Open the full entry, both organizations funded by private donations and working together to improve Zcash’s cryptography; Tachyon then led the formal verification of the Ironwood zk-SNARK, implementing the new circuit changes, funding two independent verification firms, zkSecurity and Formal Land, and connecting their work to its own machine-checked Lean proofs of the Halo 2 construction.⁠[9][10][9][9][11]

On July 28, the day Ironwood activated as NU6.3, the team published a machine-checked proof written in Lean, with more than 2,700 theorems, showing that Ironwood has no undetectable counterfeiting bugs (up to cryptographic assumptions); three research teams took more than a month to complete it. On August 14, Tachyon applied to the Coinholder Retroactive Grants Program for $738,942 for this work, including $225,000 in external audit and formal verification fees, and on September 29 Bowe thanked coinholders for approving the grant.⁠[12][12][9][9]

Project Tachyon develops the Zakura Zcash full node together with Valar Group; the two teams are primarily responsible for improving Zcash’s scalability and were the main force behind implementing and coordinating Ironwood. On September 28, Tachyon announced it was beginning to upstream its recursive proofs into Zakura’s Common cryptography stack, releasing an initial set of Zakura crates that absorb mature components of Ragu.⁠[13][14][14]

On September 29, 2026, the project team explained how Tachyon shrinks the nullifier set validators must maintain: by introducing epochs, note nullifiers change per epoch and validators keep only a small rolling window of recent history, while for older history wallets prove that none of their note’s earlier nullifiers appeared on-chain. On October 1, Shielded Labs’ newly announced post-quantum cryptography project, Epoch, said it would work closely with Sean Bowe, Tal Derei and the rest of the Project Tachyon team to keep the efforts aligned.⁠[15][15][15][16]

Project Tachyon says Tachyon can shrink transactions by two orders of magnitude and remove runaway state growth for validators, with full post-quantum privacy as a side effect. In today’s protocol every validator must permanently store all revealed nullifiers, growing by gigabytes per day even at modest transaction volumes; Tachyon’s oblivious synchronization has a remote service incrementally build a proof that funds have not been spent, without ever learning the user’s actual nullifiers, because the protocol forces them to evolve periodically in an unlinkable way. PCD also lets block producers aggregate shielded transactions without user coordination. To work with the existing ecosystem, including hardware wallets, it preserves backward compatibility with existing cryptography.⁠[17][18][18][18][18]

The roadmap has four parts: Ragu, the foundational PCD scheme, must go through several rounds of optimization and auditing before deployment; the payment protocol is decoupled from the shielded protocol, with one approach using private information retrieval (PIR) and post-quantum key exchange and another exploring note delivery via dedicated infrastructure; the new shielded protocol will first be deployed on a test network as a new pool independent of the existing Orchard pool; and mainnet activation will follow once community consensus is reached and ZIP requirements are met.⁠[19][19][19][19][19]

As of October 2026, the Project Tachyon team consisted of Lead Cryptographer Sean Bowe along with Tal Derei, Connor O’Hara, Alex Xiong, L Winslow and Samuel Akinosho. Its operating entity, Tachyon Foundation, has been funded by private donations from Zcash coinholders and has formed a 501(c)(4) organization in Wyoming that is seeking IRS approval. Tachyon is positioned as a Zcash upgrade proposal actively developed by community members and, like all network upgrades, requires community approval before activation.⁠[20][9][9][17]

Project Tachyon: Official website: https://tachyon.z.cash/ (opens in a new window).⁠[6]

X: Public account: https://x.com/TachyonZcash (opens in a new window)⁠[6]

GitHub: Public account: https://github.com/tachyon-zcash (opens in a new window)⁠[17]