When you've completed the game, you can start a new playthrough with developer commentary enabled. If you haven't beaten the game, be warned that some commentary may spoil puzzle solutions.

Throughout the first part of the escape sequence, you'll find commentary nodes from:

[Kim Swift] In these new areas, we weren't using the surfaces the player is familiar with. The rules for which new surfaces portals can be placed on and which surfaces are off-limits, needed to be taught. So we created this area both to show the player they have escaped into the 'guts' of the facility and to re-train them in which surfaces are valid for portal placement.

[Ellen McLain] I went to Portal's, umm... I Googled 'Portal in-game,' and I went to the trailer. And I just loved it! I loved hearing my voice! [Laughter] And as I told the production team, I have never played a computer game in my life. But I want to play this one! [Laughter]

[Realm Lovejoy] After players escape, we let them solve an old chamber in a new way. This reintroduction of a familiar space, which can now be solved in an 'incorrect' way, helps convey the sense that players are cheating the system while forging their own path through the facility.