Meter Contract Code Size And Increase Limit

Abstract

This EIP increases the contract code size limit from 24KB (24576 bytes) introduced in EIP-170 to 64KB (65536 bytes), and adds gas metering for excess code loading. It introduces a gas cost of 2 gas per (32 byte) word for contract code exceeding 24KB, allowing deployment of contracts of any size while preventing DoS attacks through appropriate gas metering. Lastly, it also commensurately increases initcode size limit from 48KB, introduced in EIP-3860, to 128KB (131072 bytes).

Motivation

EIP-170 introduced a 24KB contract code size limit to prevent potential DoS attacks, as large contract code requires O(n) resource cost in terms of disk reads, VM preprocessing, and Merkle proof sizes, all of which are not directly compensated by gas fees. However, this limit restricts legitimate use cases for large contracts.

This EIP proposes a gas-based solution that allows contracts of larger size while ensuring that users loading large contracts pay gas proportional to the additional resources they consume. This approach aligns with Ethereum's gas model philosophy of paying for the resources consumed. A new limit has been set at 64KB, so that raising the gas limit does not break assumptions in the p2p layer.

Improving developer experience is the primary motivation for increasing the contract size limit. The current 24KB ceiling forces developers to split functionality across multiple contracts, introduce proxies or delegatecall-based indirection, and rely on architectural patterns like the Diamond Standard—even when those patterns aren't otherwise necessary. These workarounds can increase code complexity, deployment costs, and audit surface. By raising the limit, developers can keep more logic in a single contract, improving readability and lowering gas usage by avoiding unnecessary cross-contract calls. This also makes smart contract development more accessible to newer developers, who can move from idea to deployment without first learning advanced contract composition patterns.

Specification

Definitions

The following values are updated:

Helpers

def ceil32(n: int) -> int:
    return ((n + 31) // 32) * 32

def excess_code_size(n: int) -> int:
    return max(0, n - 0x6000)

Behavior

1. Update the EIP-170 introduced MAX_CODE_SIZE constant of 24KB (0x6000 bytes) to 64KB (0x10000 bytes).
2. Introduces a new cold/warm state for contract code. Specifically, change the gas schedule of operations that load code, e.g. the opcodes CALL, STATICCALL, DELEGATECALL, CALLCODE and EXTCODECOPY are modified so that dynamic EXCESS_CODE_COST= ceil32(excess_code_size(len(code))) * GAS_PER_CODE_WORD // 32 gas are added to the access cost if the code is cold. When the code is an EIP-7702 delegation to another account, if target account code is cold add additional gas should be accounted. Warming of the contract code is subjected to the journaling and can be reverted similar to other state warming in EIP-2930.
3. Update the EIP-3860 introduced MAX_INITCODE_SIZE limit of 48KB (0xc000 bytes) to 128KB (0x10000 bytes).
4. If a large contract is the entry point of a transaction, the cost calculated in (2) is charged before the execution and contract code is marked as warm. This fee is not calculated towards the initial gas fee. In case of out-of-gas halt, execution will stop and the balance will not be transferred.
5. Empty code ( with keccak("") = "0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470") is always considered warm.

COLD_ACCOUNT_ACCESS_COST, COLD_SLOAD_COST, and WARM_STORAGE_READ_COST are defined in EIP-2929.

Migration

This EIP adds a new field to the account tuple, codesize. That is, the account tuple goes from having the following four fields, (nonce, balance, storage_root, code_hash) to (nonce, balance, storage_root, code_hash, codesize). The reason for this is that most key-value databases in use by production clients do not allow peeking at the size of a value pointed to by a given key without actually loading the full contents of the value.

To avoid forcing a full migration, the following rules are followed:

1. Any account created or updated on or after FORK_BLKNUM should additionally have its codesize written into the account tuple.
2. Any account which does not have the codesize field is assumed to have codesize less than 24KB.

Rationale

The gas cost of 2 per word was chosen to account for:

1. The additional disk I/O for retrieving larger contract code
2. The increased computational resources for preprocessing larger code for execution (a.k.a. "JUMPDEST analysis").
3. The growth in Merkle proof sizes for blocks containing larger contracts

This EIP introduces the gas cost as an additional cost for contracts exceeding 24KB. It could have been specified as a simpler ceil32(contract_size) * GAS_PER_CODE_WORD // 32, without hardcoding the existing contract size limit. However, for the sake of being conservative and avoiding lowering the cost of loading existing contracts (which could be small, under the 24KB limit), the 24KB floor was added to the formula.

The EXTCODECOPY opcode could theoretically be exempt from this, since clients could just load the parts of the bytecode which are actually requested. However, this might require a change at the protocol level, since the full code is required for the block witness. For this reason, EXTCODECOPY is included in the pricing scheme, and a carveout could be considered at a later date.

The new limit has been set at 64KB. The limit has been put in place so that increasing the gas limit won't have unexpected side effects at the db or p2p layer. For instance, in devp2p, the maximum packet size is 10MB (https://github.com/ethereum/devp2p/blob/5713591d0366da78a913a811c7502d9ca91d29a8/caps/eth.md#basic-operation). As of time of this writing, the maximum packet size in snap sync is even lower, at 96KB.

The limit for initcode has also been increased to 128KB, following the pattern set in EIP-3860 that the initcode limit is double the runtime code limit. While initcode is different from deployed code in that it does not live in the state and therefore isn't visible in devp2p or in the db, fully removing the limit could have unforeseen consequences.

Backwards Compatibility

This EIP introduces additional gas costs for certain operations. Specifically, CALL, STATICCALL, DELEGATECALL, CALLCODE, EXTCODESIZE, and EXTCODECOPY may now require extra gas when accessing cold contract code.

Test Cases

Reference Implementation

Security Considerations

Copyright

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