ERC-7964 author Ernesto García opened a pull request on October 23 proposing a breaking change to crosschain signatures. The revision would remove a domain-fields byte from the signature header and make the verifier determine which fields belong in the main signing domain.
ERC-7964 describes an EIP-712 message covering operations on multiple chains. Each chain receives an array of operation hashes and the full message data relevant to its own operation. The standard remains Draft; it was originally created in June 2025.
Domain fields would come from the verifier
Under the revision, a verifier would declare chainFields, a bitmap describing which domain fields its chain-specific structures already bind. It would derive the remaining main-domain fields using applicationFields & ~chainFields, with the application's fields obtained through eip712Domain().
García's discussion update gives a concrete example: application fields 0x0f and chain fields 0x0c produce 0x03, leaving name and version in the main domain. The chain bitmap must include the chainId bit.
The header would still occupy 32 bytes
The proposed header contains a ten-byte magic value, a two-byte operation index and a 20-byte application address. The currently published draft instead uses a nine-byte magic value and a separate one-byte fields bitmap alongside that index and address.
The outer signature envelope would remain an ABI-encoded tuple containing the header, operation hashes and signature. Its reference verification function would gain a chainFields argument. The author says the new detector would no longer recognize the old encoding.
The pull request remains open and unmerged. It proposes a specification change; it does not establish wallet adoption or deployment.