It seems like Left 4 Dead 3 is in development after Valve Concept Artist Tristan Reidford posted a tutorial for importing assets to the company’s new Destinations platform. Reidford included a screenshot that includes his recently viewed folders and one of the files said ‘left4dead3’. After many noticed it, he quickly took the screenshot down and replaced it with a different one.
What also adds fuel to this fire is that the Left 4 Dead 2 beta has been updated many times in recent memory.
