Copies of the OS X Lion Golden Master — that is, the commercial release — have arrived at Apple Retail stores on hard drives, ready to be installed into staff workstations and demo computers, MacRumors reports.

There will be no retail boxed copy of Lion, with the new operating system only available via the Mac App Store, requiring users to install the most recent version of Snow Leopard first.

An overnight is expected to begin tomorrow after the store closes, other sources report. An overnight is an Apple term used to describe a lock-in of sorts where employees stay in the store overnight to learn about new products and prepare for the next day’s launch.

If the sources are right, it looks like we’ll be set for a Lion launch on Wednesday. There’s no accompanying word as to whether the heavily-rumored Macbook Air refresh will drop on the same day as Lion or several days afterwards.