For the patch itself, see August 13, 2009 Patch.
Classless Update banner TF2
"After setting a new standard for Lack of Class in an FPS with the addition of Jarate (the jar-based Karate), we've raised the bar on lowering the tone even further with the first ever Classless Update!"
Robin Walker

The Classless Update, officially known as The First Ever Classless Update, was the first non-class specific major update. The content focus of the update differed from previous updates; instead of introducing new weapons or achievements, the Classless Update added new hats, game modes, and maps, while also delivering a large number of bug fixes and minor tweaks to existing gameplay.

The Classless Update was released in the August 13, 2009 Patch.