Bitcoin Cash’s May 2025 network upgrade delivered two consensus-layer improvements that make contracts more powerful while keeping validation predictable and fast. Together, they enable simpler smart contract design, unlock new cryptographic use‑cases, and reduce transaction sizes and fees for many existing applications.
Note on CHIPs
CHIPs (Cash Improvement Proposals) are the process for proposing and reviewing Bitcoin Cash changes before activation. For discussion and history, visit Bitcoin Cash Research.
The Two Enhancements in May 2025
- CHIP‑2021‑05 — Targeted Virtual Machine Limits
Spec: GitHub – CHIP‑2021‑05: Targeted Virtual Machine Limits
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What changed
- Replaced the legacy “201 operations per script” limit with an Operation Cost Limit that tracks realistic costs per input (including base instruction cost, bytes pushed to the stack, hashing, signature checks, and certain arithmetic operations).
- Raised the stack element size limit from 520 bytes to 10,000 bytes (matching consensus script size), enabling larger data and proofs in contracts.
- Introduced explicit density limits for hashing (digest-iteration based) and retained a direct control‑stack depth limit of 100 for OP_IF/OP_NOTIF.
- Kept SigChecks limits unchanged while unifying accounting so worst‑case costs remain predictable and safe for nodes.
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What this enables
- Larger stack items let contracts include bigger hash preimages, post‑quantum signature payloads, zero‑knowledge proofs, and more complex settlement data directly in script.
- The cost‑based model removes the old 201‑op bottleneck, so advanced contracts don’t need awkward multi‑input workarounds that complicate auditing and increase transaction size.
- Clear, explicitly‑defined density limits make worst‑case validation predictable across implementations, reducing DoS risk without adding a “gas” system.
- CHIP‑2024‑07 — BigInt: High‑Precision Arithmetic
Spec: GitHub – CHIP‑2024‑07: BigInt (High‑Precision Arithmetic)
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What changed
- Removed the VM number length limit (nMaxNumSize). Numeric operands and results are now constrained only by the existing 10,000‑byte stack element limit, with arithmetic costs accounted by the VM Limits CHIP.
- Eliminated overflow behavior tied to fixed‑width numbers and relies on operation‑cost accounting to preserve predictable validation.
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What this enables
- Native, high‑precision math in contracts without emulation. This simplifies contract code and review, reduces attack surface from precision/overflow bugs, and often shrinks transaction sizes versus emulated math.
- More capable DeFi primitives: AMMs and DEXs with precise pricing math, decentralized stablecoins with robust collateralization logic, and cross‑chain/sidechain bridges that require exact arithmetic.
- Cryptographic protocols that benefit from big integers, e.g., commitments, accumulators, and novel signature schemes, can be modeled more directly on‑chain.
Innovation Highlights
- Simpler, safer contracts: Removing precision‑emulation logic reduces code size and complexity, improving auditability and maintainability. Fewer moving parts means fewer places for bugs.
- Lower fees in practice: Contracts that previously emulated big‑number math can now rely on native operations, often reducing transaction byte size and associated fees.
- Future‑proof cryptography: Bigger stack items plus high‑precision arithmetic open the path to post‑quantum schemes, zk‑proof integrations, and other advanced cryptographic constructions as libraries mature.
- Predictable performance: Density‑based limits for hashing and operation cost deliver a consistent safety margin for nodes while expanding what contracts can do.
Activation
Both CHIPs activated in the May 2025 upgrade window:
- Previewed earlier on chipnet at MTP 1731672000 (2024‑11‑15T12:00:00Z).
- Activated on mainnet at MTP 1747310400 (2025‑05‑15T12:00:00Z), and likewise on testnet3, testnet4, and scalenet.
See each spec for details and changelogs.
Summary
The May 2025 upgrade gives Bitcoin Cash contracts both more room to express complex logic and the arithmetic precision to do it cleanly. Targeted VM Limits modernizes how the VM meters work, unlocking larger data and advanced cryptography without sacrificing node performance. BigInt removes the last major arithmetic constraint, enabling native high‑precision math that reduces complexity and fees across many applications.
Together, these enhancements strengthen BCH as a high‑throughput, low‑fee platform for payments, tokenization, and increasingly sophisticated on‑chain protocols.
