Robinhood Chain block.number vs eth_blockNumber

Last updated: October 24, 2026

Endpoint and plans: Robinhood Chain RPC endpoint.

At a glance

What you see

A contract's block-based logic disagrees with what the explorer and your RPC show. A vesting schedule or a cooldown written in blocks runs far longer than planned, a per-block limit lets many transactions through in what your backend sees as different blocks, a value stored from block.number does not match the blockNumber in the transaction's receipt, or a helper contract's getBlockNumber() returns a number tens of millions lower than eth_blockNumber.

Why this happens

Robinhood Chain is an Arbitrum Nitro Layer-2, and Robinhood's differences page says that block.number "returns an estimate of the L1 (Ethereum) block number, not the Robinhood Chain block number" and "updates only periodically". Arbitrum's reference explains the mechanism: the value is "close to (but not necessarily exactly)" the parent chain's block number and is synced with Ethereum "every 13 to 15 seconds (occasionally longer)", so it is "unreliable in the shorter term (minutes)". JSON-RPC works the other way round: eth_blockNumber, a block's number field and a receipt's blockNumber are all the L2 block number, and the L1 estimate appears in an extra l1BlockNumber field. Inside a contract, the L2 number is available from the ArbSys precompile, ArbSys(0x0000000000000000000000000000000000000064).arbBlockNumber(). The gap is not small: many L2 blocks are produced for every Ethereum block, so in the capture below the L2 counter and the L1 estimate differ by more than 61 million, and block.number stayed on one value for 81 L2 blocks before moving on by two. Local test networks model Ethereum, where both numbers are the same, so the bug survives compilation and unit tests.

Three block numbers, one block

What to do

1. Search the contracts for block.number and classify each use: a time measure, an L2 block counter, or a value you compare with off-chain data.
2. Time measures — timelocks, vesting, auction windows, cooldowns: rewrite them with block.timestamp. Arbitrum sets the timestamp per L2 block from the sequencer's clock and it never decreases.
3. L2 block counters — per-block limits, "one action per block", IDs or nonces derived from the block: call ArbSys(0x…64).arbBlockNumber() instead of block.number.
4. Values compared with off-chain data — anything stored on chain and later matched against a receipt's blockNumber or eth_blockNumber: store arbBlockNumber(), because the RPC side is always the L2 number.
5. Confirmation depth: do not count confirmations in the contract with block.number. Count them off chain by comparing the receipt's blockNumber with eth_blockNumber; both are L2 numbers.
6. Helper contracts: a multicall's getBlockNumber() returns block.number and therefore the L1 estimate; Arbitrum's own reference warns that such helpers "may exhibit unintended behavior" out of the box.
7. Before shipping, check the three values on the live chain with the calls below rather than in a local simulator.

interface ArbSys {
    function arbBlockNumber() external view returns (uint256);
}

uint256 l2Block = ArbSys(address(100)).arbBlockNumber(); // 0x…64
uint256 l1Estimate = block.number; // Ethereum block estimate, not the L2 block

curl -s "$RH_RPC_URL" -H "Content-Type: application/json" -d '[
  {"jsonrpc":"2.0","id":1,"method":"eth_blockNumber","params":[]},
  {"jsonrpc":"2.0","id":2,"method":"eth_call","params":[{"to":"0x0000000000000000000000000000000000000064","data":"0xa3b1b31d"},"latest"]},
  {"jsonrpc":"2.0","id":3,"method":"eth_getBlockByNumber","params":["latest",false]}
]'
# id 1: L2 head            e.g. "0x53a11ae"
# id 2: arbBlockNumber()   e.g. "0x…053a11ae" (same L2 number)
# id 3: result.l1BlockNumber e.g. "0x18f8d72" -> what block.number returns

When this is not our problem

The meaning of block.number, the ArbSys precompile and the l1BlockNumber field are defined by Robinhood Chain's Arbitrum Nitro stack; every RPC provider, Triport included, returns the same values for the same block. To run the checks above against Robinhood Chain mainnet on Triport, set RH_RPC_URL to the keyed URL form https://triport.io/r/<YOUR_KEY>/robinhood.