chainConfig reference

The full chainConfig contains the standard Ethereum genesis/fork fields, but the Chain SDK's prepareChainConfig() only exposes a small subset for customization. Everything else is filled from hardcoded defaults and should not be changed.

When you call prepareChainConfig, you pass a chainId (top-level) and an arbitrum object where InitialChainOwner is required and the fields below are optional overrides.

Example:

import { prepareChainConfig } from '@arbitrum/chain-sdk';

const chainConfig = prepareChainConfig({
  chainId: 123_456,
  arbitrum: {
    InitialChainOwner: '0xYourChainOwnerAddress', // required
    // Optional overrides (defaults shown):
    InitialArbOSVersion: 51,
    DataAvailabilityCommittee: false,
    MaxCodeSize: 24576,
    MaxInitCodeSize: 49152,
  },
});

Customizable fields (via prepareChainConfig)

Field	Type	Description
chainId	number	Required. The unique chain ID for your chain.
InitialChainOwner	string	Required. Address that owns the chain and holds upgrade/admin privileges.
InitialArbOSVersion	51	The ArbOS version the chain launches with.
DataAvailabilityCommittee	false	false = Rollup (L1 data posting); true = AnyTrust (DAC)
MaxCodeSize	24576	Max deployed contract bytecode size in bytes (default matches Ethereum's EIP-170 limit).
MaxInitCodeSize	49152	Max init/constructor code size in bytes (default matches EIP-3860).

Intentionally not customizable

prepareChainConfig deliberately excludes Arbitrum-specific fields so they keep their defaults:

Field	Type	Description
EnableArbOS	true	Must stay enabled.
GenesisBlockNum	0	Genesis block number.
AllowDebugPrecompiles	false	Debug precompiles; must stay disabled.

Standard fields

For informational purposes only

The following fields are populated automatically from the SDK's hardcoded defaults. They are standard Ethereum genesis/fork-activation parameters and are not exposed for customization by prepareChainConfig.

Changing these fields can produce an invalid or non-functional chain configuration.

Leave them at their default values.

Field	Default	Description
homesteadBlock	0	Block at which the Homestead fork activates.
daoForkBlock	null	DAO fork block (disabled).
daoForkSupport	true	Whether the chain supports the DAO fork rules.
eip150Block	0	Activation block for EIP-150 (gas cost changes).
eip150Hash	0x0000…0000	Hash associated with the EIP-150 fork.
eip155Block	0	Activation block for EIP-155 (replay protection).
eip158Block	0	Activation block for EIP-158 (state-clearing changes).
byzantiumBlock	0	Activation block for the Byzantium fork.
constantinopleBlock	0	Activation block for the Constantinople fork.
petersburgBlock	0	Activation block for the Petersburg fork.
istanbulBlock	0	Activation block for the Istanbul fork.
muirGlacierBlock	0	Activation block for the Muir Glacier fork.
berlinBlock	0	Activation block for the Berlin fork.
londonBlock	0	Activation block for the London fork.
clique.period	0	Clique PoA block period (seconds).
clique.epoch	0	Clique PoA epoch length.