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Configure and optimize gas

To configure gas behavior on an Arbitrum (Orbit) chain using the Arbitrum Orbit SDK, you primarily use the ArbOwner precompile (at address 0x0000000000000000000000000000000000000070), which allows the chain owner to manage key parameters via function calls. These are called with post-deployment using tools like cast (from Foundry) or a custom script with a library like ethers.js or viem. The defaults inherit from the parent chain or standard Nitro settings, but it is possible to customize your Arbitrum chain as they are permissioned by design.

Below is a breakdown of each specified parameter, including its role, typical defaults (based on Arbitrum One), and how to configure it. Note that changes may require careful consideration to avoid impacting chain performance, user experience, or security. For example, setting limits too high could lead to state bloat or slower block processing.

Gas speed limit​

  • Description: This is the target gas consumption rate per second that the chain can sustainably handle. It influences the congestion mechanism: if gas usage exceeds this limit, the base fee rises to throttle demand; if below the limit, the cost decreases (down to the floor). ArbOS uses this to update gas pools and enforce dynamic per-block gas limits.
  • Default: 7,000,000 gas/second.
  • Configuration: Call the setSpeedLimit(uint256 newSpeedLimit) method on the ArbOwner precompile, where newSpeedLimit is the desired gas per second.

Example using cast:

cast send --rpc-url $ORBIT_RPC --private-key $OWNER_KEY 0x0000000000000000000000000000000000000070 "setSpeedLimit(uint256)" $NEW_SPEED_LIMIT

This setting is adjustable post-deployment. Any modifications should align with your node's capabilities to prevent issues with the congestion mechanism activating.

Refer to the Chain parameters page, or the Additional configuration parameters for additional information.

Block gas limit​

  • Description: This limits the maximum amount consumable by all transactions in a single L2 block - for execution, not for the parent chain data availability (DA) fee charge. It helps control block size and processing time. In practice, ArbOS enforces a dynamic limit based on the speed limit and gas pools, but this sets a hard cap.
  • Default: 32,000,000 gas per block.
  • Configuration: Call the setMaxTxGasLimit(uint256 newLimit) method on the ArbOwner precompile, where newLimit is the desired max gas. This method is described as setting the block limit, although technically it may focus on per-transaction limits; in practice, it caps block usage.

Example using cast:

cast send --rpc-url $ORBIT_RPC --private-key $OWNER_KEY 0x0000000000000000000000000000000000000070 "setMaxTxGasLimit(uint256)" $NEW_LIMIT

This setting is adjustable post-deployment. Setting it too high can harm user experience due to longer block times.

Refer to the Chain parameters page, or the Additional configuration parameters for additional information.

Gas price floor​

  • Description: This is the minimum L2 base fee (in wei per gas unit), preventing fees from dropping too low during periods of low activity. The actual base fee fluctuates based on demand, but it will not fall below this set floor. It will affect user transaction costs.
  • Default: 0.1 gwei (100,000,000 wei).
  • Configuration:
    • During deployment: Set the minL2BaseFee field in the Orbit setup script's config JSON.
    • Post-deployment: Call the setMinimumL2BaseFee(uint256 newMinBaseFee) method on the ArbOwner precompile, where newMinBaseFee is the value in wei.

Example using cast:

cast send --rpc-url $ORBIT_RPC --private-key $OWNER_KEY 0x0000000000000000000000000000000000000070 "setMinimumL2BaseFee(uint256)" $NEW_FLOOR_IN_WEI

You can query the current floor via the ArbGasInfo precompile's getMinimumGasPrice().

Refer to the Chain parameters, Additional configuration parameters, or the How to manage the fee parameters pages for additional information.

Per batch gas cost​

  • Description: This refers to the fixed L1 base charge applied for the overhead of posting each batch to the parent chain. It is used in transaction pricing to amortize the parent chain's fixed costs (like calldata posting) over the batch's transactions. It can be adjusted to reflect actual posting costs or incentivize batching. The surplus (if any) gets rewarded to the batch poster.
  • Default: Varies based on parent chain fees, but typically around 210,000 gas (adjustable to match).
  • Configuration: Call the setPerBatchGasCharge(int64 newCharge) on the ArbOwner precompile, where newCharge is the fixed gas units per batch. This configuration adjusts the allocation of L2 gas for batch overhead in pricing. Additionally, you can configure related surplus fees (extra reward to batch poster) via setL1PricingRewardRate(uint64 rate). The parent chain base fee estimates influence the actual cost, which is dynamic; therefore, monitor them via ArbGasInfo's getPricesInWei() method.

Example using cast (for per batch charge):

cast send --rpc-url $ORBIT_RPC --private-key $OWNER_KEY 0x000000000000000000000000000000000000000070 "setPerBatchGasCharge(int64)" $NEW_BATCH_COST

This configuration is adjustable post-deployment. When working with layers or parent chains, you may need to further configure the data availability setup.

Refer to the How to manage the fee parameters page for more information.

Caution

Always test changes on a devnet or testnet Arbitrum (Orbit) chain, as misconfiguration can lead to unexpected fee behavior or chain instability. Refer to the ArbOwnerPublic precompile for reading current settings without modifications. If using a custom gas token, ensure configurations are compatible.