chainConfig reference

Reference list of chainConfig JSON parameters available when deploying or managing your Arbitrum chain.

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.

chainConfig reference

Customizable fields (via prepareChainConfig)Copy Anchor Link

Intentionally not customizableCopy Anchor Link

Standard fieldsCopy Anchor Link

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Customizable fields (via `prepareChainConfig`)

Intentionally not customizable

Standard fields