Read usage (headers only)

The start of the window, RFC 3339 with a time zone — 2026-08-01T00:00:00Z. A stamp without one is refused rather than guessed at, because the zone that would be assumed is ours and not yours. Defaults to the start of the billing period, so send it together with to when you are asking about a period that has closed — to on its own is measured from the current period and refuses. When you send NEITHER bound and the billing period is longer than 62 days, the default is the most recent 62 days of it rather than a refusal, because you did not choose that window; from and to in the response say so. Records go back about 399 days, to a UTC day boundary: the refusal names the exact instant, and asking from that instant works. An older from is refused rather than answered with the zeroes an expired ledger would otherwise produce. A from at or after the present instant is a 400 too: that period has not started yet.

The end of it, same format. Defaults to now — always now, so omitting it always measures up to the present instant and never to the end of a period that has closed. A to in the future is answered as now too — the response says which instant was used. The window itself may be at most 62 days: every hypervisor replays its ledger a day at a time to answer, so a longer one THAT YOU NAMED is refused rather than quietly shortened — you chose it and can narrow it. The default window is the one exception, because you did not choose it: a billing period longer than 62 days is measured over its most recent 62 and from/to report that. Two billing periods is the pair a reconciliation compares; an older period is still readable by naming both bounds.