 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 . 
