According to what said by Ready at Dawn a few months ago, The Order: 1886 uses MSAA 4x as a main anti-aliasing solution, but a tweet by Engine Programmer Matt Pettineo hints to the very solid possibility that Ready at Dawn may have added on top of the popular and quite costly technique:

You know you've been working on temporal AA too much when you start to see jittering in real life.

Temporal anti-aliasing is a technique aiming to reduce the effect of temporal aliasing, which is basically slight but disturbing flickering that happens when objects move very fast on the screen.

This seems to indicate that Ready at Dawn is probably using a solution similar in concept to Nvidia's advanced TXAA (available for instance in Watch_Dogs on PC, only for Nvidia cards), which is basically a mix of MSAA and Nvidia's own temporal filters.

That is in line with what said today by Multiplayer.it forums user Arioch82, who is known to be an Italian developer working on the game. He firmly denied the possibility of a downgrade of the game's visuals from what we previously saw:

Anyway, you're just imagining this downgrade. Things are only getting better

We're definitely going to see that for ourselves soon, as tomorrow the embargo for new previews and for the high quality version of the gameplay video showcased a few days ago will be lifted. We'll stand by and see if the nitpickers will finally be satisfied.