ValarDragon Proposes 8 MB Blocks and Tachyon Pool for Zcash NU8

Zcash contributor ValarDragon has proposed a package of protocol changes for the network's NU8 upgrade, targeted for late January 2027, headlined by a fourfold increase in the block-size limit and a new shielded pool called Tachyon. The post presents the ideas as proposals, not as an approved upgrade plan.

The headline numbers are straightforward. The block-size ceiling would rise from 2 MB to 8 MB. Combined with the Tachyon shielded pool, ValarDragon projects throughput of roughly 200 shielded transactions per second. That is a step change for a network whose current shielded capacity sits far below payment-card scale — 200 transactions per second works out to more than 17 million shielded transfers per day, a volume Zcash has never processed.

What does the proposal actually change?

Three structural items stand out for practitioners:

• Block size: a move from 2 MB to 8 MB, directly raising throughput headroom for both transparent and shielded activity.
• Tachyon shielded pool: a new privacy pool designed alongside the larger blocks to deliver the projected 200 shielded transactions per second.
• Extensible transaction format: a format intended to avoid adding distinguishability for hardware wallets that have not upgraded — an operational concern for custody stacks, since distinguishable transactions can leak metadata about which devices signed them.

The proposal also reaches into cryptography. It calls for work on post-quantum privacy and transparent opcodes built on SPHINCs variants at 128-bit and 192-bit security levels. For teams planning long-horizon custody, the inclusion of post-quantum primitives signals where the protocol's security roadmap is heading.

Economic and compatibility mechanics

ValarDragon proposes moving the NSM redistribution date to approximately the seventh halving. The stated rationale: the shift could delay the tail-emissions problem by one or two additional halvings. That is a monetary-policy adjustment, not a technical one, and it would extend the window before Zcash faces the economics of a near-zero block-subsidy regime.

A second change would set a fixed date to stop Sapling deposits while keeping Sapling transactions and withdrawals enabled — a staged wind-down that lets users exit the older pool without forced migration on a single deadline.

The final item targets a chronic operational pain point. The proposal would remove consensus branch ID updates, which ValarDragon says cause wallets to break during network upgrades. Wallet developers and exchanges running Zcash integrations know this failure mode well: each past upgrade has required coordinated software changes to avoid transaction rejection.

What does this change for practitioners now?

Nothing immediately. These are proposals for NU8, not an agreed specification, and Zcash network upgrades follow a community process of ZIP drafting, review and activation scheduling before anything ships. Exchanges, wallet providers and node operators have a long lead time — but the direction of travel is legible: larger blocks, a new shielded pool, post-quantum groundwork and fewer breaking changes at activation.

Teams maintaining Sapling-only infrastructure should begin assessing migration paths, and custody architects should track whether the SPHINCs-based opcode work survives review. The practical deadline to watch is the NU8 specification window: proposals that fail to reach consensus well before the envisioned late-January 2027 activation date will slip to a later upgrade.