At the Apple Let's Rock Event on September 9, 2008, the iPod nano 4th Generation was officially announced.

Physical features
It returns to the narrow form factor of the 2G model, while retaining and rotating the 2-inch (51 mm) screen from the 3G model.
It is also thinner than both the 2G and 3G, measuring 90.7 mm (3.6 inches) tall by 38.7 mm (1.5 inches) wide by 6.2 mm (0.24 inch) thick, and weighing 36.8 grams (1.3 ounces).
It has a curved aluminum shell and glass screen.

The six previous colours (silver, charcoal, mint, turquoise, berry red, and rose pink) have been replaced by silver, black, purple, light blue, green, yellow, orange, red, and pink. Apple markets the new colours as "nano-chromatic".

Accelerometer
Also added is an accelerometer which allows the nano to switch between portrait and landscape display modes by just tilting the iPod left or right, shuffle songs when shaken, and access Cover Flow when tilted sideways.

User Interface
The UI has also been refreshed, adding a more stylised look in keeping with the new hardware design. It includes a new voice recording feature which starts automatically when an Apple compatible microphone is plugged in. It also includes the new "Genius" feature, introduced by Apple the same day. The Genius feature automatically creates playlists based on a selected song using an algorithm built by Apple.

Environmentally Friendly
It is additionally touted as "the most environmentally friendly iPod Apple has ever made", containing arsenic-free glass and a BFR-, mercury-, and PVC-free design. It is also claimed to be highly recyclable.

Models
The iPod Nano 4G will be shipped in cases similar to the 2G ones with the clear view in the front, and is marketed in two models: 8 GB and 16 GB.
Limited quantities of an unannounced 4 GB model have surfaced in various markets.