Apple rolled out Software Update 1.0 for its newest-generation MacBook Air (mid-2013), which addresses most notably, the unstable WLAN performance. A bug in the software causes Wi-Fi connections to drop or slow down, and the update fixes that. It also addresses a rare screen-flickering bug, and one that causes audio levels to jump during video playback. Apple's slick change-log reads as:
This update fixes an issue that in rare instances may cause an intermittent loss in wireless connectivity, an issue with Adobe Photoshop which may cause occasional screen flickering, and an issue which may cause audio volume to fluctuate during video playback.
Your supported MacBook Air should auto-update whenever it's next scheduled to look up for updates; though if you're in a hurry, you can find the 3.5 MB update here.