Following yesterday's announcement, Apple has posted a beta build of OS X 10.9 (codenamed "Mavericks") to its developer site so that said developers (and interested parties with a developer account) can download it and begin testing their applications. Historically, these early developer previews haven't looked or run exactly the same as the final versions of the software. However, the system requirements—and thus the list of Mac models that will be supported by the new release—tend to remain the same from the first beta to the final release (with very few exceptions).

Assuming that this continues to be true for OS X 10.9, one MacRumors forum poster has outed the system requirements for Mavericks. Breaking with recent tradition, the list appears to be identical to the compatibility list for OS X 10.8:

The OS X v10.9 Developer Preview supports the following Macs: iMac (Mid-2007 or later)

MacBook (13-inch Aluminum, Late 2008), (13-inch, Early 2009 or later)

MacBook Pro (13-inch, Mid-2009 or later), (15-inch, Mid/Late 2007 or later), (17-inch, Late 2007 or later)

MacBook Air (Late 2008 or later)

Mac Mini (Early 2009 or later)

Mac Pro (Early 2008 or later)

Xserve (Early 2009)

Each recent OS X release has dropped support for a fairly wide swath of older Macs: OS X 10.6 dropped support for PowerPC Macs, 10.7 dropped support for Intel Macs without 64-bit CPUs, and 10.8 dropped all Macs that didn't support 64-bit EFI. According to this early list, however, any Mac that runs 10.8 should be able to upgrade to 10.9 when it comes out in the fall.

It's worth noting that not all of the listed Macs support all of OS X 10.8's features (AirDrop, which requires specific Wi-Fi capabilities, is one of the most prominent), and the same may continue to be true of some of OS X 10.9's new additions. However, users whose four, five, or even six-year-old Macs (in the case of the 2007 iMac) are still chugging along will doubtlessly appreciate the ability to run Mavericks without dropping at least a thousand dollars on new Mac hardware.