Yesterday American Airlines decommissioned their old award calendar. The airline confirmed to me that it was supposed to be gone for good.
However as commenter DJ pointed out yesterday evening there’s still a way to access this tool that lets you display award availability across a month by award type, something the new calendar does not offer.
If you go to American’s advanced flight search, make sure to click ‘redeem miles’ and then select the multi-city tab, your search will pull up the old calendar.
The old calendar, of course, will not display premium economy awards and won’t display American Airlines non-changeable premium cabin awards that aren’t priced via the award chart, so you may want to use both sets of booking tools in your searches.