- Hedera is updating its Mirror Node API for smart contract calls to improve consistency and accuracy.
- The upgrade introduces modular execution and matches contract behavior between consensus nodes and mirror nodes.
- Changes include stricter account alias handling, payer balance checks, more detailed error responses, and refined gas estimates.
- Most changes take full effect by September 1, 2025, with some updates delayed until December 1, 2025.
- Developers must test and update their applications to avoid disruptions and can preview changes on Hedera’s test networks.
Hedera will launch significant updates to its Mirror Node API endpoint, specifically for smart contract calls, starting September 1, 2025. This update, outlined in HIP-1217, impacts the /api/v1/contracts/call endpoint, aiming to deliver more accurate and reliable contract execution for developers and users.
The coming changes will roll out a modular execution flow for Hedera’s Ethereum Virtual Machine (EVM). This approach aligns mirror nodes (which simulate contract execution) more precisely with consensus nodes (which finalize transactions), addressing discrepancies seen in the previous monolithic system. According to Hedera, this will result in more precise gas use estimates, improved consistency, and enhanced debugging with clearer error codes.
Among the updates, calls using a Number Alias—a special format for identifying accounts—will now fail if a Keccak-256 alias exists for a given account. This means developers must check and use the correct account alias. The evm_address field from the mirror node API or the contractAccountId field from the Hedera SDK should be used to confirm the proper alias. For ECDSA accounts, the Keccak-256 alias must be used unless a rare exception applies.
Developers should also note that contract calls may now fail with an INSUFFICIENT_PAYER_BALANCE error if the payer account does not have enough balance. New error handling will return more specific messages, such as INVALID_CONTRACT_ID, and require updates in client-side applications. For gas estimates, users will notice slight but more accurate differences, especially when deploying contracts.
Additional impacts include changes to how contract calls return default values and KYC (Know Your Customer) status, which will now reflect the true state of consensus nodes. Error codes for certain failed operations will also change, for example, returning CONTRACT_REVERT_EXECUTED instead of previously used codes.
These changes are not backward compatible, and Hedera urges developers to thoroughly test their applications in the Previewnet and Testnet environments, where the modularized flow operates at full capacity. Mirror node operators can enable this new logic early by adjusting relevant environment variables as described in the technical guidance.
Timeline details show that most updates—including error codes, gas estimates, and KYC status handling—will be fully enforced by September 1, 2025. Address resolution and payer balance validation will go live on December 1, 2025. Teams needing extra time can request temporary access to legacy functionality by contacting the relevant support via Discord (handle: reccetech).
Full technical documentation and upgrade guidance are available at the official Hedera blog and the HIP-1217 proposal.
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