Blocks
Block endpoints read arc.blocks. They lag the chain head by two blocks so a response is unlikely to be reorganised.
Latest
http
GET /v1/arc/blocks/latest
By height
http
GET /v1/arc/blocks/{height}height 0 is genesis. A height that has not been indexed returns 404, not an empty object. A height that was reorganised and not yet repaired returns 409 with the previous hash.