Extreme Programming teams are in it for the long term. They work hard, and at a pace that can be sustained indefinitely. This means that they work overtime when it is effective, and that they normally work in such a way as to maximize productivity week in and week out. It’s pretty well understood these days that death march projects are neither productive nor produce quality software. XP teams are in it to win, not to die.
For more information, review the XP archetype.
(Source: Ron Jeffries)