(UPDATED APRIL 9, 2013)…Google has rolled out its new Compose and Reply experience in Gmail. The new default Compose allows you to write messages in a cleaner, simpler experience that puts the focus on your message itself, not all the features around it. The new compose experience opens a window at the bottom of your inbox. Here are some of the highlights:

• Fast: Compose messages right from your inbox
• Simple: Redesigned with a clean, streamlined look
• Powerful: Check emails as you’re typing, minimize drafts for later, and even compose two messages at once

The Compose and Reply experience is now default on IIT Gmail. For a limited time, users may switch back to the old experience at any time. Steps to opt-out from the new Compose experience are:
1. Click Compose
2. At the bottom corner of the message pane, click the More menu icon next to the Discard button.
3. Select “Switch back to old compose”

Can users opt-out permanently? No. The new Compose experience will become the only Compose and Reply experience in Gmail by late April.

Will this new Compose be available to IE8 or basic HTML users? No. The new Compose experience will not roll out to users on IE8 or using the basic HTML view.

More details on Google’s support page.