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  • Ethereum Interview Question: How Do Protocol Upgrades Impact Deployed Smart Contracts?

    Ava Martin

    Member

    Updated: May 27, 2025
    Views: 71

    How do Ethereum protocol upgrades, like new EIPs or hard forks, affect smart contracts that are already deployed on the network?

    In a recent Solidity interview, I was asked this and realized I’m not sure about the specifics. I’ve worked on DeFi and NFT projects, but I haven’t had to handle protocol upgrades directly.

    Do live contracts keep running as before, or do developers need to take action when Ethereum changes things like opcodes or gas costs?

    If you’ve faced this during an upgrade, how did you deal with it?

    Any advice or real-world examples would help.


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  • amanda smith

    Member • 3w

    Yep, your live Ethereum smart contracts will usually keep running after protocol upgrades like new EIPs or hard forks. The contract code itself doesn’t change. But things can still get weird if the upgrade changes how the EVM works.

    For example, if an upgrade tweaks gas costs or updates opcodes, your contract might start behaving differently. I saw this during the Istanbul hard fork. Some contracts that relied on fixed gas amounts just stopped working. It was a mess for anyone who didn’t test ahead of time.

    If your contract is pretty standard, you’re probably fine. But if you depend on specific gas costs or certain opcodes, you need to pay attention. For DeFi and NFT projects, I always recommend using upgradeable proxies or at least having a migration plan. Watch for new EIPs.

    Test your code on testnets before any mainnet upgrade. Don’t assume you’re safe—Ethereum protocol upgrades can break things, and it’s better to be prepared.

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