Apple today seeded build 12F26 of OS X 10.8.5 to developers, marking the sixth beta iteration of 10.8.5. The release comes exactly one week after the previous OS X 10.8.5 beta, build 12F23.
As with previous betas, the update contains no known issues and can be downloaded via Apple's Developer page or through the software update tool of the Mac App Store. It is also available to AppleSeed members with a new version of Safari.
Apple's OS X 10.8.5 beta is being tested along side the next version of the operating system, OS X Mavericks. Apple has thus far seeded four developer previews of Mavericks and plans to offer the new operating system to the public in the fall.