Historical observations, oldest first. At most 15360 points are used; longer histories are truncated to the most recent window. Gaps are rejected rather than filled — decide how to handle a missing observation before asking for a forecast.

Pandas offset alias for the series ('MS' month start, 'QS', 'D', 'W-SUN'). Inferred from dates when omitted.

Label for the series, echoed back in the response.

ISO dates aligned one-to-one with values. When supplied, forecast rows are dated by extending the series frequency.

Steps to forecast. Must be between 1 and 1024.

Named covariates known only over the history. Each must have the same length as values.

Named covariates known over history and forecast window, such as a calendar or a published projection. Each must have length len(values) + horizon.