Apple today seeded build 12F20 of OS X 10.8.5 to developers, offering a fourth version of the next Mac operating system update for testing. The release comes one week after the appearance of the previous beta of OS X 10.8.5, build 12F17.

Mountainlion12f20
As with previous betas, the update comes with no known issues and can be downloaded via Apple's Developer Page or through the software update tool in the Mac App Store.

Testing on OS X 10.8.5 comes as Apple is also continuing work on its next major version of OS X, Mavericks. Apple has already seeded three developer previews of OS X Mavericks and has announced that it will launch the new operating system to the public this fall.

Update: One tipster says the update fixed the Adobe Photoshop flickering issue that was reported last last month.

Top Rated Comments

gnurf Avatar
159 months ago
A pretty irrelevant post considering this a about Mavericks, not iOS.

Except it isn't about Mavericks :)
Score: 7 Votes (Like | Disagree)
HolgerR Avatar
159 months ago
A pretty irrelevant post considering this a about Mavericks, not iOS.

No. It's not.
Score: 3 Votes (Like | Disagree)
ValSalva Avatar
159 months ago
Will there be a 10.8.6?

Yays? Nays?

I think yes. 10.8.5 will be out well before Mavericks. Then work on 10.8.6 will begin. I highly doubt there will be any 10.8.7 though.
Score: 2 Votes (Like | Disagree)
cbs20 Avatar
159 months ago
Have any of you guys any experience in how things are running with the latest 10.8.5 vs the 10.9 dev ?

I had the first 10.9 dev build installed and it runs like a dream, but things like some adobe apps breaks, but I would hate going back to 10.8 (standard) because that was dreadful too... so currently i am running windows8.1 but would prefer to get back on a speedy osx :)

So if any of you for some reason have had too much time and have a feeling of both, let me know! thanks :P

First thing you have to consider is 10.8 is a much more established OS and 10.9 is only in beta. When DP1 for 10.9 was released that was the first time anybody at Adobe could get their hands on the OS and start optimizing applications to run in 10.9. On top of that the OS is constantly changing until its final release and applications may need to be tweaked with these changes to make sure they work with the OS. You can't make a good comparison of a beta OS to an established OS. Wait until 10.9 is released and app developers release their updates and then you can judge what OS to use.
Score: 1 Votes (Like | Disagree)
Mr. Wonderful Avatar
159 months ago
^As much as I hate waiting longer for new releases, I think year and a half OS X development cycles might be a good thing for everyone. It's more time to add more significant features, and it allows more time for the current OS to become rock solid, which is great for casual users and enterprise. I know I felt like Lion never got truly stable.
Score: 1 Votes (Like | Disagree)
Garrod Avatar
159 months ago
They should do weekly iOS 7 beta seeds too.

A pretty irrelevant post considering this a about Mavericks, not iOS.
Score: 1 Votes (Like | Disagree)

Popular Stories

iPhone 17 Pro 3 4ths Perspective Aluminum Camera Module 1

New iPhone 17 Pro Details: Brighter Display, Best Battery Life, and More

Wednesday September 3, 2025 5:33 am PDT by
Apple's iPhone 17 Pro and iPhone 17 Pro Max models will feature a number of significant display, thermal, and battery improvements, according to new late-stage rumors. According to the Weibo leaker known as "Instant Digital," the iPhone 17 Pro models will feature displays with higher brightness, making it more suitable for use in direct sunlight for prolonged periods. The iPhone 16 Pro and...
iPhone 17 Pro Iridescent Feature 2

iPhone 17 Pro Clear Case Leak Reveals Three Key Changes

Sunday August 31, 2025 1:26 pm PDT by
Apple is expected to unveil the iPhone 17 series on Tuesday, September 9, and last-minute rumors about the devices continue to surface. The latest info comes from a leaker known as Majin Bu, who has shared alleged images of Apple's Clear Case for the iPhone 17 Pro and Pro Max, or at least replicas. Image Credit: @MajinBuOfficial The images show three alleged changes compared to Apple's iP...
iphone 16 pro ghost hand

iPhone 17 Pro: 5 Reasons Not to Upgrade This Year

Monday September 1, 2025 4:35 am PDT by
Apple will launch its new iPhone 17 series this month, and the iPhone 17 Pro models are expected to get a new design for the rear casing and the camera area. But more significant changes to the lineup are not expected until next year, when the iPhone 18 models arrive. If you're thinking of trading in your iPhone for this year's latest, consider the following features rumored to be coming to...
iPhone 17 Pro Iridescent Feature 2

iPhone 17 and iPhone 17 Pro Prices Estimated Ahead of Apple Event Next Week

Tuesday September 2, 2025 1:50 pm PDT by
Just one week before Apple is expected to unveil the iPhone 17 series, an analyst has shared new price estimates for the devices. Here are J.P. Morgan analyst Samik Chatterjee's price estimates for the iPhone 17 series in the United States, according to 9to5Mac: Model Starting Price Model Starting Price Change iPhone 16 $799 iPhone 17 ...
iPhone 17 Pro Dark Blue and Orange

iPhone 17 Release Date, Pre-Orders, and What to Expect

Thursday August 28, 2025 4:08 am PDT by
An iPhone 17 announcement is a dead cert for September 2025 – Apple has already sent out invites for an "Awe dropping" event on Tuesday, September 9 at the Apple Park campus in Cupertino, California. The timing follows Apple's trend of introducing new iPhone models annually in the fall. At the event, Apple is expected to unveil its new-generation iPhone 17, an all-new ultra-thin iPhone 17...
iOS 18 on iPhone Arrow Down

Apple Preparing iOS 18.7 for iPhones as iOS 26 Release Date Nears

Sunday August 31, 2025 4:35 pm PDT by
Apple is preparing to release iOS 18.7 for compatible iPhone models, according to evidence of the update in the MacRumors visitor logs. We expect iOS 18.7 to be released in September, alongside iOS 26. The update will likely include fixes for security vulnerabilities, but little else. iOS 18.7 will be one of the final updates ever released for the iPhone XS, iPhone XS Max, and iPhone XR,...
iPhone 17 Pro on Desk Centered 1

Survey: Nearly 70% of Users Plan to Upgrade to iPhone 17

Monday September 1, 2025 8:24 am PDT by
A new survey has found that nearly seven in ten iPhone owners in the United States plan to upgrade to an iPhone 17 model, signaling strong demand ahead of Apple's expected unveiling of the devices at its September 9 keynote. Smartphone price comparison platform SellCell surveyed over 2,000 U.S.-based iPhone users in August to assess upgrade interest and brand loyalty before Apple's event....