When selecting OrderDescending, the output get's written as OrderAscending. Extract: .DateHistogram("someAggregation", mpy => mpy .Field("someField") .Interval("year") .OrderDescending("_key") raw output: "date_histogram": { "field": "someField", "interval": "year", "format": "yyyy-MM-dd", "order": { "_key": "asc" } }