There has not been a dedicated thread for Hotel Chicago Downtown, Autograph Collection, although the hotel has been discussed in other threads on FlyerTalk's Marriott forum. Most Autograph Collection properties, especially in major cities, have their own thread. Now this one does too.

Here's the official link with the current description, photos, map, and so on:

Marriott.com: Hotel Chicago Downtown, Autograph Collection

Let's get some confusion out of the way, right way. There's another Marriott-affiliated property, a half mile to the northeast, with a very similar name. Different hotel. Different brand ("AC" is not an abbreviation for "Autograph Collection"). Different FlyerTalk thread: FlyerTalk: AC Hotel Chicago Downtown

Hotel Chicago Downtown, Autograph Collection is one of three Autograph Collection properties in Chicago. The other two are The Blackstone, Autograph Collection (former Renaissance Blackstone) and Hotel EMC2, Autograph Collection (a boutique hotel themed to art and science). Given the success of the Autograph Collection brand and the number of distinctive full-service hotels in Chicago not affiliated with a major brand, there will probably be more in the future.

Hotel Chicago Downtown, Autograph Collection is part part of the Marina City complex, famous for its twin "corncob" towers, along the Chicago River. When the complex opened in 1967, the current hotel was an office building. The current House of Blues in the complex was a movie theater.

Through an adaptive reuse transformation in 1998, the office building became the House of Blues Hotel, a Loews Hotel. The hotel became the Hotel Sax around 2007.

Then, in early 2014, the hotel joined Marriott's Autograph Collection, becoming Hotel Chicago Downtown, Autograph Collection.

The location is excellent for business and Chicago tourism. I've never stayed there, but I've been inside several times. Shortly, after joining Autograph Collection, the hotel seemed rather odd. But when I was there in late 2017, everthing had been renovated with a modern, stylish decor.