A signature lookup can return 404 after a direct completion. Treat a missing signature as unavailable; direct response signatures are not a production verification gate.
Preserve exact request and response bytes
Build the request body once and retain the exact bytes sent by the client. Retain the raw response bytes before parsing JSON or Server-Sent Events.
Do not parse and re-serialize JSON, normalize whitespace or line endings, omit stream delimiters, or reconstruct a streamed response from parsed events. The signature covers the uncompressed response body. Request Accept-Encoding: identity, or hash the body after your HTTP client decompresses it.
Fetch and verify the signature
Set <CHAT_ID> to the id in the completion response whose exact bytes you retained.
Set <SIGNING_ALGO> to the explicit algorithm used for the matching model attestation.
For ecdsa, recover the Ethereum EIP-191 signer from text and signature, then compare it with signing_address. For ed25519, verify the UTF-8 bytes of text using signing_address as the public key. Reject unsupported algorithms.
Then require that text is exactly:
Use the model_name reported by the direct model attestation. A different string, even if it resembles the hostname or a NEAR AI Cloud gateway model ID, does not satisfy this check. If the report has no non-empty model_name, this direct response-signature format cannot be verified.
Use the manual response-signature helpers with the exact request and response bytes, this model_name, and the signer from the verified direct model attestation.
Match the model signer
Request or select a direct model attestation whose signing_address and signing_algo exactly match the signature. Verify its quote, client-generated nonce, signer binding, and required workload policy as described in direct model attestation. A matching signer does not establish that the report and completion came from the same serving instance.
Do not infer a gateway or model classification from the format of the signed text, and do not substitute a report for a different signer.
ecdsa identities are Ethereum-style signing addresses. ed25519 identities are Ed25519 public-key bytes encoded as hexadecimal. Always compare the identity together with signing_algo.