Bitcoin Cash Upgrade History
A chronological timeline of BCH upgrades to date, upcoming changes and active proposals.
After 2017's blocksize increase that led to the split and the upgraded chain renaming, BCH continued upgrading the Bitcoin Script and its Virtual Machine to be programmable sound money.
2017-2018 · Survival & Scaling Foundations
2017
Bitcoin user activated hard fork becomes BCH — August 2017
The upgrade increased Bitcoin's block size to 8 MB in response to growing adoption and removed Replace‑by‑Fee (RBF), but ended up being the minority chain and having to rename. Without transaction queue or fee market, transactions are instant in practice (0-confirmation finality).
Impact: restored Bitcoin's ability to function as money in addition to as a store of value (BCH).
Difficulty Adjustment Algorithm — November 2017
The DAA replaced the previous Emergency Difficulty Adjustment (EDA) to provide a more stable and predictable mining difficulty schedule.
Impact: ensured a more steady and consistent block production every 10 minutes in the face of hashrate fluctuations.
2018
Monolith, block size increase to 32 MB — May 2018
This upgrade raised the maximum block size limit to 32 MB, establishing Bitcoin Cash’s on-chain scaling path and increasing transaction capacity. It also began restoring key scripting features—reviewed and updated for safer use.
Impact: enabled more on-chain payments at scale and paved the way for smarter contracts without sacrificing safety.
Re-enabled and modernized OP_CAT, OP_SPLIT, OP_AND/OR/XOR, OP_DIV/MOD, OP_NUM2BIN, OP_BIN2NUM, with reviews and safer design adjustments where needed.
CVE-2018-17144 fix — September 2018
An inflation vulnerability in Bitcoin Core 0.14–0.15 stemming from duplicated‑input handling was disclosed by Bitcoin Cash developer Awemany on September 17th, 2018. A fix was issued within hours and the bug was never exploited on either BTC or BCH chain.
CTOR and Magnetic Anomaly — November 2018
CTOR made transaction ordering deterministic, improving block propagation and parallel validation. Magnetic Anomaly also added OP_CHECKDATASIG, enabling contracts to validate external data.
Impact: helped blocks propagate faster and enabled contracts to validate external data—expanding what developers can build on BCH.
CTOR requires all non-coinbase transactions to be sorted lexicographically by transaction ID. Magnetic Anomaly also introduced OP_CHECKDATASIG / OP_CHECKDATASIGVERIFY, allowing scripts to verify signatures over arbitrary data.
2019–2020 · Script Revival & Protocol Hardening
2019
Great Wall — May 2019
This upgrade introduced Schnorr signatures, replacing ECDSA and making signatures more efficient and flexible. It improved multisig behavior and opened the door to better privacy and contract designs.
Impact: improved efficiency and expanded the design space for better privacy and contracts in the future.
Schnorr signatures enable signature aggregation and more advanced multisig constructions, reducing transaction size and verification cost. They also make some privacy-preserving protocols and contract patterns simpler to implement compared to ECDSA.
Graviton — November 2019
Extended Schnorr support to multisig, improving how complex spending conditions and shared wallets work on BCH. It also tightened malleability-related consensus rules to strengthen security and future-proof contract capabilities.
Impact: made multisig safer and more efficient while strengthening the protocol for more advanced smart-contract use.
Updated OP_CHECKMULTISIG and OP_CHECKMULTISIGVERIFY to accept Schnorr signatures. The upgrade also reinforced malleability-related consensus rules, reducing edge-case risks and improving safety for complex contract patterns.
2020
Phonon — May 2020
The Phonon upgrade introduced SigChecks — a precise signature‑verification cost model replacing SigOps — and added OP_REVERSEBYTES, expanding Bitcoin Cash’s scripting capabilities.
Impact: made transaction validation more predictable and efficient, enabling more sophisticated contracts without compromising safety.
SigChecks replaces the older SigOps counting method with a more accurate signature-validation cost model. This helps prevent edge-case DoS vectors and makes resource limits more predictable for complex scripts.
Implementation details: Bitcoin Cash Node v0.21.0 release notes→
Axion — November 2020
Axion introduced ASERT (ASERTi3-2d), a new difficulty adjustment algorithm that reduced hashrate-driven swings and made block timing more consistent.
Impact: kept block production steadier during hashrate swings, making the network more reliable and predictable.
2021–2022 · Programmable Bitcoin Emerges
2021
BigBlockIfTrue — May 2021
Improved block validation and mempool handling for more consistent performance under high throughput. Also enabled multiple OP_RETURN outputs per transaction, supporting cleaner protocol experimentation without unnecessary UTXOs.
Impact: made BCH nodes handle heavy throughput more smoothly and enabled cleaner protocol metadata.
2022
Update 8 — November 2022
Enabled contracts to introspect the spending transaction, unlocking more practical covenant designs. Also expanded arithmetic (OP_MUL + 64-bit integers), making smart contracts more expressive and efficient.
Impact: expanded what BCH smart contracts can safely verify and compute on-chain.
U8 introduced transaction-introspection opcodes for contracts to read properties of the spending transaction (including outputs/recipients), reducing complexity and inefficiency in earlier covenant constructions. It also re-enabled OP_MUL and expanded integer math from 32-bit to 64-bit for more capable contract logic.
Implementation details: Bitcoin Cash Node v24.0.0 release notes→
2023–present · Smart contracts & dynamic blocksize
2023
Cashtokens — May 2023
CashTokens introduced native token primitives and covenant-based smart contracts directly into the BCH protocol. Tokens now operate with the same guarantees as BCH itself, enabling on-chain DEXs and other financial applications with high assurance.
Impact: enabled native tokens and permissionless DeFi to run directly on BCH with the same security guarantees as the base currency.
CashTokens add token primitives directly to the BCH protocol, rather than relying on external virtual machines or wrapped assets. This means tokens inherit BCH’s validation rules and security model, enabling covenant-based contracts such as DEXs, stablecoins, AMMs, vaults, and other permissionless financial applications.
Implementation details: Bitcoin Cash Node v25.0.0 release notes→
2024
Adaptive Blocksize Limit Algorithm — May 2024
Introduced an adaptive block size limit that adjusts automatically to network demand, replacing manual block-size decisions with automatic BCH scaling→ based on demand.
Impact: removed block-size governance debates by turning scaling into a predictable protocol rule.
2025
Velma — May 2025
VMLA upgraded Bitcoin Cash’s virtual machine to a more capable and extensible design, improving execution safety and enabling richer smart-contract behavior. It also laid a cleaner foundation for future opcode and covenant development.
Impact: made BCH’s contract engine safer today and easier to extend tomorrow.
Upcoming Bitcoin Cash 2026 upgrade: Layla
Layla introduces the next generation of scripting and virtual‑machine enhancements. It adds loops (OP_BEGIN / OP_UNTIL), modular contract functions (OP_DEFINE / OP_INVOKE), re‑enabled and extended bitwise opcodes, and Pay‑to‑Script standardization — significantly increasing smart‑contract expressiveness while preserving execution safety and predictable resource limits.
Layla CHIPs:
With these upgrades, Bitcoin Cash continues advancing the original mission of Bitcoin: to serve as decentralized sound money and a global economic system without intermediaries or hierarchies.
Proposals under discussion for future upgrades can be found at bitcoincashresearch.org→