Respawn Entertainment has posted a new job listings on Gamasutra seeking to fill staff positions for Titanfall and an "unannounced title". The four positions include a visual FX artist, a senior level designer, and a senior & mid-level software engineer.
There are no clues in the entries themselves that hint as to what the unannounced title may be, save for a cryptic requirement about "breathing life into the gameplay world and helping define the moment to moment player experience."
There's a strong possibility that the unknown title is Titanfall 2, a project that has been all but officially announced. Both Electronic Arts and Respawn hope to make Titanfall a lucrative franchise. However, even if it is Titanfall 2, there are many questions about whether the game will include a real single player mode or not, or if it might feature an open world.
Titanfall is Respawn's first and currently only game release. It was launched back in March 2014 to great fanfare. The game was very influential, as games have taken pages from its unique mech-and-parkour gameplay, most notably Black Ops III.