Pre-Fork Gas Audits: Simulating Sweeps Before Glamsterdam

According to CoinDesk, Ethereum developers delayed a Glamsterdam test after security developers flagged a risk to existing contracts. If you run EVM sweep or forwarding contracts, start a gas audit now. Record what each call path consumes today, compare that against any gas value your contracts or sweeper service hardcode, and reprice sweep thresholds before a fork date is reset. Simulation measures today's rules. Testing proposed rules still requires a devnet that runs the fork.

The problem

The delay is the signal. When protocol developers pause a test because existing contracts are at risk, teams with deployed bytecode should assume their own contracts belong in scope.

Backend engineers at exchanges and payment service providers (PSPs) are most exposed. A typical deposit stack on Ethereum runs one forwarding contract per deposit address, plus a sweeper service that flushes ERC-20 balances into a hot wallet. That bytecode is immutable. Gas assumptions inside it cannot be patched after deployment.

Those assumptions surface in four places:

• A fixed amount of gas forwarded in a low-level call from the forwarder to a token contract or treasury.
• Native transfers that rely on a fixed gas stipend reaching a receiving contract.
• Loops in batch sweep functions that stop early when remaining gas drops below a hardcoded floor.
• Off-chain gas limits hardcoded in the sweeper service, often with a thin multiplier.

There is precedent. EIP-1884, shipped in the Istanbul upgrade, raised the gas cost of state-reading opcodes, and the proposal itself warned that contracts relying on fixed gas amounts could break. A repricing does not have to be large to push a forwarder with tight margins into out-of-gas reverts.

The second failure is economic. If a sweep consumes more gas, the balance below which sweeping a deposit address loses money moves upward. Sweep thresholds set against old gas numbers quietly turn small deposits into negative-margin operations.

What you need

• An inventory of every contract and call path: forwarder flush, single ERC-20 sweep, batch sweep, native coin forward.
• Source code or verified bytecode for each contract, so you can locate every hardcoded gas value.
• A recent mainnet transaction hash for each call path, to anchor estimates in real execution.
• A Crypto APIs key. The free tier needs no credit card.
• Access to a devnet or testnet running the proposed fork client. This is the hard part. Our simulator executes against the live rules of the network you target. It does not model unshipped Ethereum Improvement Proposals (EIPs).
• A clear chain scope. The simulation endpoint covers Ethereum only. For other EVM chains such as Polygon or Arbitrum One, use gas-limit estimation instead.

How it works

Step 1: Anchor to history. For each call path, fetch a recent transaction with GET /transactions/evm/{blockchain}/{network}/{transactionHash} and its internal calls with GET /transactions/evm/{blockchain}/{network}/{transactionHash}/internal. The internal view matters for forwarders, because the gas that reaches the token contract is the number a repricing squeezes. Record gas used per path.

Step 2: Simulate the current call. The transaction simulator executes an unsigned transaction against current Ethereum state without broadcasting it. Run each sweep path against a representative deposit address.

POST https://rest.cryptoapis.io/simulate-transactions/evm/ethereum/mainnet
X-API-Key: <your key>
Content-Type: application/json

Take the request body and response fields from the product documentation. We are not reproducing them here. The output you need is execution success and gas consumed for each path.

Step 3: Estimate gas limits across chains. For forwarders on chains outside Ethereum mainnet, POST /blockchain-fees/evm/{blockchain}/{network}/estimate-contract-interaction-gas-limit returns a gas-limit estimate for a contract call. POST /blockchain-fees/evm/{blockchain}/{network}/estimate-token-transfer-gas-limit covers plain ERC-20 transfers. Compare both against the values hardcoded in your sweeper service.

Step 4: Price the sweep. Pull current EIP-1559 fee data from Blockchain Fees:

GET https://rest.cryptoapis.io/blockchain-fees/evm/ethereum/mainnet/eip-1559
X-API-Key: <your key>

Multiply gas used by the fee level you actually broadcast at. Then convert the cost into the deposit currency using Market Data. The result is your break-even sweep threshold per token. Our guide to gas estimation for forwarding on EVM venues walks through that conversion.

Step 5: Compute headroom. For every hardcoded gas value, divide measured consumption by the hardcoded amount. Paths with thin headroom are your fork risk list. When a proposed repricing is published, rerun Steps 2 and 3 on a devnet running that client and compare the deltas.

Step 6: Control your node timing. On shared infrastructure, client upgrades follow the network schedule. With dedicated nodes, you run a single-tenant JSON-RPC (remote procedure call) endpoint and can coordinate client upgrade timing with our team. That matters when a fork date moves, as this one already has.

What to watch for

• State dependence. Gas consumption varies with state. Writing to an empty storage slot costs more than updating a populated one. Accessing a token contract cold costs more than accessing it warm. Simulate the worst case, such as a token's first-ever balance on a fresh deposit address, not only the common case.
• Current rules only. A clean simulation on mainnet says nothing about post-fork behavior. Treat mainnet results as the baseline and devnet results as the test.
• Thin multipliers. A sweeper that sets gas limits at estimate times 1.05 will fail first. Store multipliers in configuration, not code, so you can widen them without a deploy.
• Stuck sweeps. If out-of-gas reverts start after a fork, replacement transactions need correct nonces. GET /addresses-latest/evm/{blockchain}/{network}/{address}/next-available-nonce returns the next nonce for the sweeping address.
• Immutable forwarders. If a deployed forwarder cannot survive a repricing, the remedy is a new forwarder and a migration of deposit addresses. Start that work before activation, not after. Our payment forwarding guide covers the deployment side.
• Moving dates. Fork schedules slip. Key audit reruns to client releases and published activation blocks, not to calendar assumptions.
• Request volume. Auditing thousands of deposit addresses is a batch job. Sample by call path and token, throttle requests, and keep results so a devnet rerun compares like for like.

The Glamsterdam delay gives contract owners time they may not get again. Use it to measure what your sweep and forwarding paths consume today, find the hardcoded gas that will not survive a repricing, and reset thresholds before activation. Start with the Transaction Simulator for Ethereum paths and Blockchain Fees for gas limits on every other EVM chain you sweep.