Bitcoin CashMay 2027 Upgrade - Proposals
Faster Blocks has entered public testing, and OP_SIGHASH has an implementation awaiting review. Native curve operations, TXv5, and post-quantum signatures remain at earlier stages. None is confirmed for the May 2027 upgrade.
- Tentative MTP target
- May 15, 2027, 12:00 UTC
- Inclusion
- Not confirmed
- Reviewed
- Oct 27, 2026
November 15, 2026 remains the proposed lock-in and chipnet activation date for Faster Blocks and OP_SIGHASH. Their tentative mainnet target is May 15, 2027 at 12:00 UTC, measured by median time past. These are proposal targets; the upgrade package is not finalized.
Proposals under discussion
Faster Blocks — public testing. The October 24 revision targets one-minute blocks, rescaling difficulty, subsidy, block-size limits, and block-based timelocks for the shorter interval. Tempnet launched October 15 with a work-in-progress BCHN implementation and public monitoring. It is a temporary fork of chipnet, separate from the proposed November chipnet upgrade.
OP_SIGHASH — implementation review. Contracts could obtain the single SHA-256 digest of a transaction's signing preimage, simplifying custom signature checks and covenants. The specification still carries a September 8 revision date. BCHN merge request !2119 remains open and unmerged; Jason Dreyzehner supported the opcode's utility on October 6, but inclusion is unconfirmed.
Native elliptic-curve arithmetic — experimental. The August 1 draft focuses on secp256k1 point addition and multiplication through OP_ECADD and OP_ECMUL. It has benchmark prototypes but explicitly no activation proposal. Opcode assignments, execution costs, independent implementations, and worst-case testing remain open.
TXv5 — draft. The published specification still targets May 2027, but its latest revision is January 29, 2025. It proposes a new transaction format with features including read-only inputs and detached signatures. Extracting read-only inputs or unified bytecode limits into smaller changes has been discussed; neither that split nor the full package is confirmed.
Post-quantum and hybrid signatures — draft and prototype. The June 10 draft proposes a signature-scheme registry and combined signatures, with SPHINCS+ and hybrid signing as initial candidates. It names a tentative May 2027 target and links a BCHN prototype. Scheme selection, verification costs, cryptographic review, and stakeholder acceptance remain unresolved.
What remains open
Faster Blocks has public support, conditional endorsements, and dissent. Review still covers propagation and orphan risk, node testing, and wallet or exchange confirmation policies. Tempnet results are early test evidence, not proof of mainnet readiness. Final inclusion depends on implementation review, testing, and ecosystem agreement; proposals may still be deferred.