4A Games announced
that after working on "a number of multiplayer prototypes" for Metro: Last Light, it has decided to move the multiplayer team back onto single-player development. As a result, Metro: Last Light will not launch with a multiplayer component, though the developer isn't ruling out the possibility it will happen post-release.
"Right now we're 100% focused on the single player campaign and not thinking beyond that," reads the post. "We don't like throwing away work though, it's a project we could potentially return to after Metro: Last Light ships."
Regarding the change of heart, 4A admits: "In hindsight, it was probably a mistake to announce it when we did, but we're an enthusiastic team and wanted to be open about what we were making!"