Submission Headers
We supports HTTP headers on the submitBlock endpoint (POST /relay/v1/builder/blocks) per the helix sourcecode.
Encoding and Compression
Standard HTTP headers control payload format:
| Header | Values | Description |
|---|---|---|
Content-Type | application/json, application/octet-stream | JSON or SSZ encoding. SSZ is recommended. |
Content-Encoding | gzip, zstd | Compress the payload body. zstd is preferred for better compression ratio and speed. |
Custom Headers
| Header | Values | Description |
|---|---|---|
x-api-key | API key string | Authenticate with a registered API key. Skips BLS signature verification for known builders, reducing processing latency. |
x-submission-type | default, dehydrated | Specifies the submission type. dehydrated enables block delta submissions. |
x-sequence | Integer | Sequence number for all submissions. Used to reject stale submissions and for cancellations. |
x-hydrate | Any value | When present, instructs the relay to return the hydrated (full) block in the response after applying deltas. Useful for debugging dehydrated submissions. |
API Keys
API keys are issued per builder public key. A valid x-api-key header allows:
- Skipping BLS signature verification (lower latency)
- Access to block delta submissions on mainnet
- Access to builder-direct endpoints (where available)
Contact us to request an API key.