That's right, Google's next developer phone is a Galaxy S4 that has been turned into a Nexus device. The device will come running stock Android -- as Nexus devices usually do -- and will be unlocked with an unlocked bootloader.
The "Nexified" GS4 will be able of running on both T-Mobile and AT&T's LTE networks. It will ship with 16GB of storage and will -- as you might expect -- be available directly from Google's Play Store. Now for the bad news: Unlike the Nexus 4, which was heavily discounted by Google, this GS4 will sell for $649, starting on June 26.
It's on par for an unlocked high-end device, but so unlike the most recent Nexus devices.
It won't ship, however, with Android 4.3. Like the current GS4s, the device will sport Android 4.2.2. Considering that the device will run stock Android, though, it will probably be the first Galaxy S4 to recieve an update to 4.3.