Also as Markdown.
The label
Data replies, /v2/sports, /v2/events and /v2/bookmakers carry an ETag: a label of the decompressed content, with -gz inside the quotes on the gzip copy. It changes when, and only when, those bytes change. /v2/pricing and /v2/openapi.json carry the body's SHA-256 instead.
The 304
Send the ETag back as If-None-Match. If the body would be the same, the reply is 304 Not Modified. It has an empty body and costs nothing, and it still counts toward the flood cap. Keep the rows you have. A call the balance can't cover is refused 402 even with If-None-Match.
Pacing
Keyed replies carry Cache-Control: private, max-age=2, must-revalidate. Poll at the pace your product needs: an unchanged board costs you only a 304.
Every statement here follows the published contract. The API reference has the full detail.