Skip to main content

Enabling blob transactions for Arbitrum batch poster

This guide explains how to configure your Arbitrum node to post EIP-4844 blob transactions to the parent chain, which can significantly reduce data availability costs.

Prerequisites​

Before enabling blob transactions, verify that your setup meets these requirements:

1. Chain configuration​

  • Your Arbitrum chain must be running in Rollup mode

2. Parent chain compatibility​

Your parent chain (typically Ethereum mainnet or a testnet) must support EIP-4844. You can verify this by checking that recent block headers contain:

  • ExcessBlobGas field
  • BlobGasUsed field

3. ArbOS version​

Your ArbOS version must be 20 or higher. To check your current version:

Method 1: Smart contract call Call the arbOSVersion() function on the ArbSys precompile contract:

  • Contract address: 0x0000000000000000000000000000000000000064
  • Function: arbOSVersion() returns uint256
  • You can call this using any Ethereum client or block explorer on your Arbitrum chain

Method 2: Using cast (if you have Foundry installed)

cast call 0x0000000000000000000000000000000000000064 "arbOSVersion()" --rpc-url YOUR_ARBITRUM_RPC_URL

If your version is below 20, upgrade by following the ArbOS upgrade guide.

Configuration​

To enable blob transaction posting, add the following configuration to your node:

{
  "node": {
    "batch-poster": {
      "data-poster": {
        "post-4844-blobs": true
      },
      "post-4844-blobs": true
    }
  }
}

After updating your configuration:

  1. Save the configuration file
  2. Restart your Arbitrum node
  3. Monitor the logs to confirm blob posting is active

Verification​

Once restarted, you can verify that blob transactions are being posted successfully by monitoring your node logs.

Log messages to look for​

When a blob transaction is successfully posted, you'll see a log entry similar to:

INFO [05-23|00:49:16.160] BatchPoster: batch sent  sequenceNumber=6 from=24 to=28 prevDelayed=13 currentDelayed=14 totalSegments=9
numBlobs=1

Key indicator: The numBlobs field shows the number of blobs included in the transaction:

  • numBlobs=0: Traditional calldata transaction was posted
  • numBlobs>0: Blob transaction was successfully posted (in the example above, 1 blob was sent)

Troubleshooting​

Why is my node still posting calldata instead of blobs?​

Your node may continue using calldata in these scenarios:

  1. Cost optimization: When blob gas prices are high, calldata posting may be more economical
  2. Batch Type Switching Protection: After a non-blob transaction is posted, the next 16 transactions will also use calldata to prevent frequent switching

Check your node logs for blob-related error messages and verify that your parent chain is accessible and fully synced.