@0xmf I think only "last_read_id" is missing. Or am I misunderstanding the question? The stream marker stuff is documented here: https://developers.app.net/reference/resources/stream-marker/, sorry it's not complete on the response envelope page.
@hutattedonmyarm And new tokens (with the public_message:net.app.core.broadcat scope) can't update the stream marker for a broadcast channel? That's definitely a less used code path, I can check on that later tonight. It _should_ work but may not.