How to Plan for EVM Chain Upgrades and Hard Forks

EVM chain upgrades and hard forks are scheduled, non-backward-compatible changes to a blockchain's protocol. Unlike soft forks, which are backward-compatible, a hard fork requires all node operators to upgrade their client software to the new version to remain on the canonical chain. For developers, this means your smart contracts, dApps, and infrastructure must be tested and potentially adjusted to ensure compatibility and security post-upgrade. Major examples include Ethereum's London (EIP-1559) and Shanghai (staking withdrawals) upgrades, which introduced fundamental changes to transaction pricing and consensus mechanics.

Proactive planning begins with monitoring official channels. Subscribe to announcements from the core development teams of the chains you build on, such as the Ethereum Foundation's blog.ethereum.org or the respective forums for Layer 2s like Arbitrum or Optimism. These sources publish Ethereum Improvement Proposals (EIPs) and release notes for client software like Geth, Erigon, and Nethermind. Key information to track includes the fork block number, a detailed changelog of EIPs included, and the final versions of client software that support the upgrade.

Your technical audit should focus on the specific EIPs being activated. For instance, if an upgrade modifies opcode gas costs (like EIP-2929) or introduces new precompiled contracts, you must analyze how these changes impact your smart contract's execution logic and gas expenditure. Use a development framework like Hardhat or Foundry to run your test suite against a local fork of the chain that simulates the post-upgrade state. This can reveal breaking changes in dependencies, such as library contracts that use deprecated opcodes or assumptions about block structure that are no longer valid.

Infrastructure readiness is critical. Node operators and RPC providers must upgrade their clients. If you run your own nodes, schedule the client software update to complete before the fork block. For services like Alchemy or Infura, confirm their upgrade timeline and any required actions on your part. Update your dApp's front-end libraries (like ethers.js or web3.js) to versions compatible with any new JSON-RPC methods introduced by the upgrade. Plan for a maintenance window around the fork block, as network instability or temporary forks can occur.

Finally, establish a rollback and communication plan. Despite thorough testing, unforeseen issues can arise. Be prepared to pause critical contract functions via pause mechanisms or migrate liquidity if necessary. Communicate clearly with your users about the upgrade schedule, expected downtime, and any actions they need to take. A well-documented post-mortem after the upgrade can improve your process for the next event. Consistent, methodical planning transforms network upgrades from a point of risk into a routine operational procedure.

An EVM chain upgrade or hard fork is a non-backwards-compatible protocol change that requires all network participants to update their client software. These upgrades introduce new features, improve performance, or implement critical security fixes. For developers building on chains like Ethereum, Arbitrum, or Polygon, failing to plan for these events can lead to downtime, broken smart contracts, and lost funds. This guide outlines the essential steps for proactive preparation, from monitoring announcements to executing a post-upgrade validation plan.

The planning process begins with active monitoring of official communication channels. Subscribe to the core development forums and announcement blogs for your specific chain. For Ethereum, this includes the Ethereum Foundation Blog and the Ethereum Cat Herders. For Layer 2s, follow their official documentation and Discord/Social channels. Track the Ethereum Improvement Proposal (EIP) process, as finalized EIPs define the technical specifications of the upgrade. Key information to gather includes the fork block number, client software versions, and a detailed migration guide.

For node operators and infrastructure providers, testing is critical. Once the new client software (e.g., Geth, Erigon, Nethermind) is released, run it on a testnet that has already implemented the upgrade. This allows you to verify that your node syncs correctly and that your monitoring and alerting systems function with the new software. Test your failover procedures and ensure your deployment scripts are updated. For consensus-layer upgrades (like Ethereum's Beacon Chain), coordinate closely with your validator client setup.

Smart contract and dApp developers must analyze the EIPs included in the fork to assess impact. Some upgrades, like EIP-1559 (London) or EIP-4844 (Dencun), introduce new opcodes or change gas mechanics, which can affect contract logic and transaction costs. Use tools like Hardhat or Foundry to run your test suite against a local fork of the chain that simulates the post-upgrade state. Pay special attention to contracts that rely on block properties (like block.difficulty), gas price estimation, or precompiled contracts that may have been modified.

Create a formal upgrade runbook for your team or project. This document should list the exact steps for deployment, including a timeline, responsible persons, and rollback procedures. Schedule a mainnet dress rehearsal on the day of the upgrade: monitor block explorers, your own nodes, and key transaction flows. After the upgrade block is mined, immediately verify that your applications are functioning. Check RPC endpoints, indexers, and any off-chain services that depend on chain data. Post-upgrade, continue monitoring for at least 24-48 hours for any latent issues.

EVM chain upgrades are proposed, discussed, and finalized through each network's specific governance process. For Ethereum mainnet, this occurs via the Ethereum Improvement Proposal (EIP) process on the Ethereum Magicians forum and subsequent decisions by core developers. For Layer 2s (e.g., Arbitrum, Optimism) and other EVM chains (e.g., Polygon, Avalanche C-Chain), you must follow their respective governance forums and GitHub repositories. The goal is to identify which EIPs are being bundled into an upcoming hard fork, often named (e.g., Prague/Electra, Dencun).

Establish a routine to monitor key information sources. For Ethereum, the primary source is the AllCoreDevs meeting notes and recordings, where implementation timelines are set. Subscribe to the Ethereum Cat Herders blog for summaries. For other chains, follow their official engineering blogs and Discord announcements. Critical data points to track include: the final EIP list, the targeted mainnet block number or timestamp for activation, and the release versions of client software (Geth, Nethermind, Erigon, Besu) that will include the changes.

Upgrades are typically announced weeks or months in advance. The timeline usually progresses from testnet deployments (e.g., Sepolia, Holesky) to mainnet. You must note the activation block/height on each testnet, as this is your primary environment for pre-mainnet testing. A common mistake is only planning for the mainnet date; your internal testing schedule must be anchored to the first testnet deployment, which gives you the earliest opportunity to validate your systems.

For developers, monitoring isn't passive. When new EIPs are confirmed, you must analyze their technical impact. For example, EIP-1153 (Transient Storage) introduces new opcodes (TLOAD/TSTORE), while EIP-4788 (Beacon block root in EVM) exposes a new precompile. This analysis dictates whether your smart contracts, front-end tooling, or infrastructure code requires modifications. Create a checklist for each EIP affecting your stack.

Automate alerts where possible. Use GitHub watch functions on client repositories to monitor release tags. Tools like the Chainlist often update with new fork information. For comprehensive, programmatic monitoring, you can use the Chainscore Upgrades API, which provides a normalized feed of upcoming hard forks across multiple EVM chains, including confirmed block numbers and affected EIPs, saving you from manual tracking across disparate sources.

Begin by mapping your application's dependencies against the upgrade's Ethereum Improvement Proposals (EIPs). For a major upgrade like the London hard fork (EIP-1559), you needed to assess impacts on transaction fee estimation, wallet integrations, and block reward calculations. Create a checklist of your application's touchpoints with the EVM: - Gas estimation and fee payment logic - Reliance on specific opcode behavior or gas costs - Dependencies on block structure fields (e.g., baseFeePerGas) - Interactions with consensus or validator-related precompiles. This mapping reveals which components require immediate attention.

Next, conduct a targeted code audit and testing. For instance, if an upgrade introduces a new precompile or modifies an existing one (like EIP-1962 for BLS12-381 operations), you must test any contract that interacts with it. Use a forked testnet of the new protocol version. Tools like Hardhat or Foundry allow you to fork the mainnet state and simulate the upgrade environment. Write specific tests that trigger the modified EVM behavior, such as sending transactions with the new fee structure or calling updated opcodes, to verify your contracts handle them correctly and gas usage remains within expected bounds.

Finally, evaluate impacts on your off-chain infrastructure and tooling. Upgrades often require updates to node client software (Geth, Erigon, Nethermind), indexers (The Graph), and RPC providers. If your dApp's backend relies on specific RPC method responses or event logs that may change, you must update your integration code. For example, the Paris upgrade (The Merge) changed the difficulty opcode to return 0 and introduced new JSON-RPC fields like finalized block tags. Plan for a coordinated update of your node infrastructure, monitoring systems, and any services that parse blockchain data to ensure continuity post-upgrade.

Testing on a devnet or testnet fork allows you to validate the upgrade's core mechanics in isolation. A devnet is a purpose-built, private Ethereum network where you have full control over the genesis block, validators, and upgrade schedule. This is ideal for initial integration testing of your smart contracts and infrastructure. Tools like Hardhat, Foundry, and Anvil make spinning up a local devnet straightforward. For example, you can use Hardhat's network configuration to fork the Sepolia testnet at a specific block and then simulate the upcoming upgrade rules.

For more realistic testing, create a fork of a public testnet like Sepolia or Holesky. This replicates the live state—including existing contracts and token balances—allowing you to test interactions with deployed protocols. Using Foundry's anvil command, you can fork Sepolia and apply the new EVM rules: anvil --fork-url https://sepolia.infura.io/v3/YOUR_KEY --fork-block-number 5500000 --hardfork cancun. This command creates a local chain that behaves like Sepolia at block 5.5M but runs with the Cancun hardfork specifications, letting you execute transactions to see how your dApp behaves under the new rules.

Your test suite should be comprehensive. Focus on state-changing operations, gas estimation, and new opcode behavior. If the upgrade introduces BLOBBASEFEE (EIP-4844) or modifies SELFDESTRUCT semantics (EIP-4758), write specific tests that call functions utilizing these features. Monitor for unexpected reverts, gas cost discrepancies, and state corruption. This is also the time to test your off-chain services—indexers, bots, and front-end integrations—against the new chain behavior.

Automate the deployment and verification process. Use scripts to deploy your contract suite to the forked testnet, run your full test battery, and verify contract bytecode. Incorporate this into your CI/CD pipeline. Services like Tenderly or Chainstack offer managed forking environments that can be integrated for automated testing. The goal is to catch issues where a contract's logic becomes invalid or a transaction's gas cost exceeds block limits post-upgrade.

Finally, participate in public testnet upgrades. When the client teams (Geth, Nethermind, Besu, Erigon) release candidate versions for the hard fork on testnets, deploy your contracts there. This tests your system in a multi-client, decentralized environment with real network conditions. Observing your application's performance during the coordinated testnet upgrade is the final dress rehearsal before mainnet.

EVM chain upgrades, including hard forks and network-wide upgrades, are scheduled events that introduce new features, optimizations, or security patches. For node operators, failing to update your client software before the activation block height results in your node syncing to a different chain, causing service disruption. The process involves monitoring official announcements from the chain's core developers, understanding the specific changes in the upgrade (e.g., EIP-4844 for proto-danksharding), and planning a coordinated update for all your node clients (e.g., Geth, Erigon, Nethermind, Besu).

Your planning should start weeks before the scheduled fork block. First, identify which clients you are running and check their official repositories (like Geth on GitHub) for release notes and compatibility information. Create a rollback plan by taking a full backup of your node's data directory and noting down your current client version. For production systems, test the new client version on a staging node synced to a testnet (like Sepolia or Holesky) to identify any configuration or performance issues specific to your setup before applying changes to mainnet.

Execution should be timed to minimize downtime. For consensus clients (like Lighthouse, Prysm, Teku), updates often require a coordinated restart of both the execution and consensus clients. The standard procedure is to: 1) Stop the node services, 2) Install or deploy the new client binaries, 3) Restart the services, ensuring they are using the updated configuration flags if required. Monitor your node's logs closely for errors and verify it begins syncing blocks again. Use public block explorers and health-check endpoints to confirm your node is on the correct chain and participating correctly post-upgrade.

Post-upgrade, conduct validation checks. Confirm your node is attesting or proposing blocks (for validators), and that its reported head block matches the canonical chain. Monitor resource usage (CPU, memory, disk I/O) as new client versions can have different performance characteristics. Subscribe to client-specific Discord channels or mailing lists for immediate post-upgrade support. Document the entire process—including the client versions, upgrade time, and any issues encountered—to refine your procedure for the next network upgrade.

Proactive, multi-channel communication minimizes user disruption and builds trust. Start by creating a single source of truth, such as a dedicated blog post or documentation page, that details the upgrade's scope, timeline, and user impact. This should clearly state the hard fork block number or timestamp, expected network downtime, and any mandatory actions like updating node software or client applications. For major upgrades like Ethereum's London (EIP-1559) or Shanghai (staking withdrawals), this central resource is essential for developers, validators, and end-users.

Your communication strategy should target all relevant audiences through their preferred channels. Announce the upgrade on your project's official Twitter/X, Discord, and Telegram channels. For technical stakeholders like dApp developers and node operators, send detailed emails and post in developer forums. Use clear, non-technical language for end-users in general announcements, focusing on what they need to do (e.g., "Ensure your wallet is updated") and what they can expect (e.g., "Transactions may be delayed during the upgrade window"). Pin these messages in community channels for visibility.

Create a timeline for your communications. Begin with an initial announcement 4-6 weeks before the upgrade, providing high-level details. Follow up with technical deep-dives 2-3 weeks prior, sharing migration guides and testing instructions. Issue final reminders 24-48 hours before the fork, and provide real-time updates during the upgrade process itself. After the fork is complete, publish a post-mortem or summary confirming network stability. Tools like Chainscore's Node Monitoring can provide public dashboards to show real-time network health during the transition, offering transparent verification.

A rollback contingency plan is not an admission of failure; it is a standard engineering practice for managing risk during a live network event. For EVM chains like Ethereum, Arbitrum, or Polygon, a hard fork or major upgrade can introduce unexpected behavior in smart contracts, RPC endpoints, or node software. Your plan should be a documented, executable checklist that your team can follow under pressure. It must specify the rollback trigger conditions (e.g., a critical vulnerability in a newly activated EIP, >30% of nodes failing to sync, or a broken state transition) and the authorized personnel who can initiate the process.

The technical core of the plan involves preparing and testing a rollback deployment. This typically means maintaining a deployment of your system's previous version, compatible with the pre-fork chain state, in a paused or dormant state. For a DeFi protocol, this could be a set of contract addresses on a testnet that mirrors the mainnet fork. Your CI/CD pipeline should allow you to quickly re-point frontends, oracles, and bots to these backup endpoints. Crucially, you must verify that all dependencies—like price feeds or cross-chain messaging layers—remain functional post-rollback, as they may also be affected by the chain upgrade.

Communication is a pillar of effective rollback execution. Your plan must include clear, pre-drafted templates for announcements to users on social platforms (X, Discord), governance forums, and via on-chain alerts if possible. Specify how you will instruct users to cease interactions with the new system and, if necessary, how to access funds or positions in the rolled-back environment. Transparency during this process is essential for maintaining trust, even if the rollback is ultimately not needed. Document every decision and action during the event for a post-mortem analysis.

To solidify your upgrade plan, create a formal checklist. This should include: - Pre-fork preparation: Testing your smart contracts and infrastructure on a testnet like Sepolia or Holesky, monitoring official channels like the Ethereum Foundation Blog for announcements, and updating client software (e.g., Geth, Nethermind, Erigon) to the compatible version. - Fork activation: Scheduling a maintenance window, having a rollback plan, and monitoring node sync status and RPC health. - Post-fork validation: Running integration tests, verifying new EIP functionality, and checking for any unexpected chain reorganizations.

For developers, the most critical action is comprehensive testing. Use a mainnet fork on a local testnet or a service like Tenderly or Foundry's anvil to simulate the upgrade environment. Deploy and interact with your contracts using the new client version. Pay special attention to any EIPs that modify opcode gas costs (like EIP-1884), introduce new precompiles (like EIP-2537 for BLS12-381), or change cryptographic behavior, as these are common sources of post-upgrade failures.

Node operators must prioritize client diversity and infrastructure readiness. Avoid running a supermajority client; instead, distribute your validators or RPC nodes across different clients (e.g., Geth, Nethermind, Besu) to mitigate consensus bugs. Ensure your hardware meets the new potential resource requirements, as upgrades like Ethereum's "Dencun" (EIP-4844) introduced new data blobs that affect storage and bandwidth. Automate monitoring alerts for block production and peer count drops.

Stay informed through the right channels. Follow the core development calls for the chain you're building on. For Ethereum, the Ethereum Magicians forum is a key resource for discussing EIPs. For Layer 2s or other EVM chains, monitor their official Discord servers and GitHub repositories. Understanding the rationale behind an upgrade, not just the technical specs, helps anticipate its broader ecosystem impact.

Your next step is to apply this framework to an upcoming upgrade. Identify the next scheduled hard fork for your primary chain (e.g., Ethereum's "Prague/Electra," Arbitrum's Nitro upgrade, or Polygon's mainnet fork). Walk through the checklist: set up a testnet node, read the relevant EIPs or improvement proposals, and run your dApp's test suite against the new rules. Proactive preparation is the most effective strategy for ensuring seamless transitions in the evolving EVM landscape.