Delta eliminated award charts a couple of years ago off of their website. They tell you the price they give to you on any given day is ‘the price’. This makes it easier to raise prices without members knowing, and since they made a happen of changing their program without notice anyway it eliminates the need to bother informing members as the value of the SkyMiles currency changes (gets worse).
Of course no matter what Delta tells you, they still price off an award chart, it’s simply hidden from view. They have buckets of availability and each bucket corresponds to a price. With partners that availability is in a single bucket, and whenever it is available it is the same price — except that Delta now bumps up pricing for certain partner awards booked close to departure.