ValveTime, a Half Life fan site, claims to be in possession of concept art from Half Life 2: Episode 3. According to the site, the art was given to it by a “unknown source” rumored to be a Valve employee.
While it is still impossible to confirm if they are real or not, the pictures do seem to follow Half Life 2’s story arc. For example, we can see Alyx wearing her father’s jacket and other clothing suited for cold climate. There is also the crashed helicopter near a research facility in an arctic environment.
If you remember, Episode 2’s ending suggested the next Half Life game will take place in a frozen surrounding, so unless this is just a fan’s attempt at teasing Valve, there might be something to those pictures. See them below for yourslef.