CHIPs · CHIP-2025-01 · draft
TXv5: Transaction Version 5
Proposes a version 5 transaction format with fractional satoshis, fractional CashTokens, detached signatures and smaller transactions.
Summary
“This proposal introduces a version 5 transaction format, enables fractional satoshis and fractional CashTokens, simplifies contracts, and optimizes transaction sizes.”
Motivation
The CHIP lists these benefits:
- Zero-overhead covenants: user-deployed financial and privacy covenants with transaction sizes matching purpose-built “layer 1” networks.
- Detached (“cross-input”) signatures: several inputs can reference the same signature, for example to sweep many coins with one signature.
- Comprehensive malleability protection: optionally covers all unlocking bytecode.
- Covenant UTXO recycling: lets covenants recover dust from obsolete outputs.
- Fractional satoshis: prepares for much larger scale, while saving up to 6 bytes per output versus today’s encoding.
- Fractional CashTokens: up to 19 extra decimal places for large, liquid tokens like stablecoins.
It builds on the restricted transaction versions rule from 2023, which reserved new version numbers for formats like this.
Current status
Draft (version 1.0.0, January 2025). In the original post, the author proposed a chipnet lock-in in November 2026 and mainnet in May 2027. He also said that if a new encoding looks too disruptive, he would propose the smaller, backwards-compatible parts for 2027 and re-propose the v5 encoding for 2028. In December 2025, kzKallisti listed it among notable CHIPs that were “incomplete and lacking consensus.” It is not locked in, and no formal stakeholder statements were found.