What changes when you port a dApp from Ethereum to Robinhood Chain

On 2026-10-13 at 12:43 UTC we asked Robinhood Chain's official public RPC for its head. eth_blockNumber answered 0x5377646 — block 87,520,838. A moment later the latest block header carried a second number, l1BlockNumber: 0x18f87df, or 26,183,647. That second number is what block.number returns inside a Solidity contract on this chain. If your contract counts blocks, measures time in blocks or derives an ID from block.number, it is now counting Ethereum blocks, and nothing in compilation, deployment or a local test run will tell you.

That is the shape of every difference in this post. Robinhood Chain's own documentation opens by saying contracts "deploy without modification, and standard tooling works out of the box" — and then lists the behaviours that differ because the chain is an Arbitrum Nitro Layer-2 rollup. Provider pages repeat the first half. This post is about the second half: nine checks, what to change for each, and one RPC call per check that shows the difference on the live network rather than in a simulator.

The nine differences in one table

The "Robinhood Chain" column is the official Differences from Ethereum page and the Transaction Finality page, both read on 2026-10-13. The last column is a call you can make against any Robinhood Chain endpoint, including the Robinhood Chain RPC endpoint on Triport.

Two rows need the full story; the others are short enough to act on from the table.

block.number: the one that breaks silently

Arbitrum's own reference on block numbers and time explains the mechanism: block.number returns a value "close to (but not necessarily exactly)" the parent chain's block number, synchronised roughly every 13 to 15 seconds, "occasionally longer". RPC clients, on the other hand, see the L2 block number in the standard number field, and the parent-chain number in an added l1BlockNumber field. So your off-chain code and your contract are looking at two different clocks, and both are called "block number".

Here is the check. The first call is an ordinary eth_blockNumber; the second is an eth_call to the ArbSys precompile at 0x…64 with the selector of arbBlockNumber() (0xa3b1b31d). We sent both in one batch on 2026-10-13:

[
  {"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":1,"result":"0x5377646"},
  {"jsonrpc":"2.0","id":2,"result":"0x0000000000000000000000000000000000000000000000000000000005377646"}
]

Both answers are 87,520,838. That is the point: arbBlockNumber() is the call your contract should make when it needs the L2 counter, and the batch proves it agrees with what RPC reports. The number a contract gets from block.number is the header's l1BlockNumber — 26,183,647 in the block we read — and it can stand still for many L2 blocks in a row.

What to rewrite: rate limits measured "per N blocks", vesting or auction windows expressed in blocks, commit–reveal schemes with block-count deadlines, and any ID built from block.number. Express time with block.timestamp, which Arbitrum sets per L2 block from the sequencer's clock, and keep arbBlockNumber() for the cases where you genuinely need to count L2 blocks.

Finality, and what our contract lets you ask for

Ethereum gives you two tags that encode protocol finality, safe and finalized. Robinhood Chain has a staged model instead. The official finality page lists three stages: a soft confirmation when the sequencer "accepts, orders, and executes your transaction and returns a receipt"; "Posted to Ethereum", typically minutes later, after which "ordering is now fixed"; and Ethereum finality, "~13 minutes after posting". Withdrawals back to Ethereum through the canonical bridge are a separate matter with a 7-day challenge period.

On Triport, the supported block tags for Robinhood Chain reads are latest, earliest, pending and hex numbers; safe and finalized are not part of the contract (see the parameter table on eth_call). And pending is not a stage either: our pending data reference calls it "a snapshot of what the sequencer presents right now", which can disappear, be replaced or move to another block.

A "read at finalized" helper carried over from Ethereum will therefore fail on this contract. That is the good outcome. The wallet backend guide spells out the replacement: record the receipt's blockNumber, compare it with the head, and treat the transaction as settled after the confirmation depth your product requires. Pick the depth per action: a UI update can follow the receipt; crediting a high-value deposit should wait for the stages the official page recommends for "high-value or irreversible actions".

The other seven, briefly

Randomness (row 2). The block we read had "difficulty":"0x1". A lottery or mint that hashes prevrandao is deterministic here. The official page suggests a dedicated oracle such as Chainlink VRF.

blockhash (row 3). It works, but only for recent blocks, per the official page. If a contract stores a block number and later reads its hash for settlement, test that path with a realistic delay, not in the same block.

Coinbase (row 4). The miner field in the header we read was 0xa4b000000000000000000073657175656e636572 — its tail is the ASCII for "sequencer". Builder-tip patterns from Ethereum MEV code that transfer ETH to block.coinbase pay the network fee account instead.

Fees (row 5). A plain transfer costs 21,000 gas on Ethereum (ethereum.org, gas docs). On Robinhood Chain the estimate for an empty transfer was 21,225 on 2026-10-13, and the official gas page says eth_estimateGas already accounts for both fee components. Hard-coded gasLimit: 21000 is the classic port bug. Fee pricing and why a tip buys nothing are covered in our priority-fee comparison.

Contract size (row 6). 96 KB of code and 192 KB of init code. This removes a pain, not adds one — unless you deploy the same bytecode to Ethereum too, where the 24 KB limit still applies. To audit a deployed contract, take eth_getCode, strip 0x and divide the hex length by two.

Ordering (row 7). First-come, first-served. Strategies that win on Ethereum by outbidding — replacement transactions with a higher tip, gas-price ladders — do nothing here. What changes for submission is the subject of a separate post.

Screening (row 8). Reads are unaffected, per the official page, and a blocked transfer "simply appears as though the event never occurred". For an indexer this is benign; for a payment flow it means a sent transaction can end with no receipt and no error. Time out on the receipt, not on an error you will never get.

The hidden one: address aliasing

The official page also notes that when an Ethereum contract sends a message to a contract on Robinhood Chain, msg.sender on L2 is "the aliased L1 address (the original address plus a fixed offset)". Access control that checks msg.sender == myL1Contract will reject every cross-chain message. The fix is to compare against the aliased form; take the offset from Arbitrum's cross-chain messaging documentation rather than from a blog post, including this one.

Why local tests pass

A local EVM simulator models Ethereum's rules: block.number ticks once per block, prevrandao varies, and the precompile at 0x…64 is usually absent. So a contract whose block arithmetic is wrong for Robinhood Chain passes every unit test. Whether your simulator emulates Arbitrum precompiles is something to check, not assume. The cheaper guard is the table above: run the nine RPC checks against the live network before you call the port finished, and add the chain to your config with the chain ID 4663 network config for MetaMask, viem and Hardhat rather than a hand-typed entry.

When this is the wrong approach

• Your contracts never read block context. A token or a vault that uses neither block.number, prevrandao, coinbase nor cross-chain messages ports with only the fee and finality changes. Do not rewrite what does not depend on these values.
• You need protocol-level finality as a tag. Our Robinhood Chain contract does not expose safe or finalized. If your architecture requires a tag rather than a depth rule, that is a design decision to make before porting, not a parameter to flip.
• You need test assets first. This post is about mainnet behaviour. The testnet (chain ID 46630 on the official connecting page) shares the precompiles but is a separate network with its own endpoints.

Sources

1. Robinhood Chain, Differences from Ethereum — https://docs.robinhood.com/chain/differences-from-ethereum/, read 2026-10-13 (block.number estimate, constant prevrandao/difficulty, blockhash, coinbase, L2 + L1 fees, address aliasing, 96 KB / 192 KB code limits vs Ethereum's 24 KB, screening, first-come, first-served ordering).
2. Robinhood Chain, Transaction Finality — https://docs.robinhood.com/chain/transaction-finality/, read 2026-10-13 (three stages, "~13 minutes after posting", 7-day challenge period).
3. Robinhood Chain, Gas & Fees — https://docs.robinhood.com/chain/gas-and-fees/, read 2026-10-13 (two components; eth_estimateGas accounts for both).
4. Robinhood Chain, Protocol Contracts — https://docs.robinhood.com/chain/protocol-contracts/, read 2026-10-13 (ArbSys at 0x…64). Connecting — https://docs.robinhood.com/chain/connecting/, read 2026-10-13 (chain IDs 4663 and 46630).
5. Arbitrum, Block numbers and time — https://docs.arbitrum.io/build-decentralized-apps/arbitrum-vs-ethereum/block-numbers-and-time, read 2026-10-13 (l1BlockNumber field, sync roughly every 13 to 15 seconds, timestamps from the sequencer).
6. ethereum.org, Gas and fees — https://ethereum.org/en/developers/docs/gas/, read 2026-10-13 (an ETH transfer requires 21,000 gas).
7. RPC responses captured from Robinhood Chain's official public RPC on 2026-10-13 between 12:43 and 12:47 UTC: eth_chainId 0x1237; eth_blockNumber 0x5377646; eth_call to ArbSys arbBlockNumber() 0x…5377646; eth_getBlockByNumber("latest") (block 0x537765a) with l1BlockNumber 0x18f87df, difficulty 0x1, miner 0xa4b0…6572; eth_estimateGas for an empty transfer 0x52e9; eth_maxPriorityFeePerGas 0x0.
8. Triport, eth_call on Robinhood Chain (supported block tags), pending data and wallet backend guide (depth-based confirmation).