 After the success of Portal, Valve decided to make Portal 2 a standalone product, partly because of pressure from other developers within Valve who wanted to work on a Portal product. Work began almost immediately after the release of Portal. Valve committed more resources to Portal 2's development than they had for the first game; Portal had a team of seven or eight people, but Portal 2 had a team of 30 or 40. The initial team of four was expanded as subgroups formed to devise game mechanics and to plot the story. Participants in internal review processes were inspired by what they saw to join the project. According to Erik Wolpaw, some Portal 2 developers worked on the Left 4 Dead games to help them meet milestones, but returned to Portal 2, "with extra people in tow." Kim Swift, Portal's designer, left Valve for Airtight Games halfway through Portal 2's development.
