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
162 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
162 months ago
A pretty irrelevant post considering this a about Mavericks, not iOS.

No. It's not.
Score: 3 Votes (Like | Disagree)
ValSalva Avatar
162 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
162 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
162 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
162 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

apple store down feature

Here's Why the Apple Store is Going Down

Thursday November 27, 2025 1:01 pm PST by
Apple's online store is going down for a few hours on a rolling country-by-country basis right now, but do not get your hopes up for new products. Apple takes its online store down for a few hours ahead of Black Friday every year to tease/prepare for its annual gift card offer with the purchase of select products. The store already went down and came back online in Australia and New Zealand, ...
iPhone Pocket Short

iPhone Pocket is Now Completely Sold Out Worldwide

Tuesday November 25, 2025 7:16 am PST by
Apple recently teamed up with Japanese fashion brand ISSEY MIYAKE to create the iPhone Pocket, a limited-edition knitted accessory designed to carry an iPhone. However, it is now completely sold out in all countries where it was released. iPhone Pocket became available to order on Apple's online store starting Friday, November 14, in the United States, France, China, Italy, Japan, Singapore, ...
streaming black friday 2025

Best Black Friday Streaming Deals - Save Big on Apple TV, Disney+, Hulu, and More

Thursday November 27, 2025 1:14 pm PST by
We've been focusing on deals on physical products over the past few weeks, but Black Friday is also a great time of year to purchase a streaming membership. Some of the biggest services have great discounts for new and select returning members this week, including Apple TV, Disney+, Hulu, Paramount+, Peacock, and more. Note: MacRumors is an affiliate partner with some of these vendors. When...
New Intel Logo

Apple and Intel Rumored to Partner on Mac Chips Again in a New Way

Friday November 28, 2025 7:33 am PST by
While all Macs are now powered by Apple's custom-designed chips, a new rumor claims that Apple may rekindle its partnership with Intel, albeit in a new and limited way. Apple supply chain analyst Ming-Chi Kuo today said Intel is expected to begin shipping Apple's lowest-end M-series chip as early as mid-2027. Kuo said Apple plans to utilize Intel's 18A process, which is the "earliest...
Apple Foldable Thumb

Foldable iPhone to Debut These Three Breakthrough Features

Tuesday November 25, 2025 7:09 am PST by
Apple's first foldable iPhone is expected to launch alongside the iPhone 18 Pro models in fall 2026, and it's shaping up to include three standout features that could set it apart from the competition. The book-style foldable will reportedly feature an industry-first 24-megapixel under-display camera built into the inner display, according to a recent JP Morgan equity research report. That...
iphone air camera

iPhone Air Flop Sparks Industry Retreat From Ultra-Thin Phones

Thursday November 27, 2025 3:14 am PST by
Apple's disappointing iPhone Air sales are causing major Chinese mobile vendors to scrap or freeze their own ultra-thin phone projects, according to reports coming out of Asia. Since the ‌iPhone Air‌ launched in September, there have been reports of poor sales and manufacturing cuts, while Apple's supply chain has scaled back shipments and production. Apple supplier Foxconn has...
streaming black friday 2025

Black Friday Streaming Deals Include Big Savings on Disney+, Hulu, Apple TV, and More

Monday November 24, 2025 8:03 am PST by
We've been focusing on deals on physical products over the past few weeks, but Black Friday is also a great time of year to purchase a streaming membership. Some of the biggest services have great discounts for new and select returning members this week, including Disney+, Hulu, Paramount+, Peacock, and more. Note: MacRumors is an affiliate partner with some of these vendors. When you click a...
General Apps Messages Redux

Singapore Orders Changes to iMessage by December

Tuesday November 25, 2025 6:39 am PST by
Singapore has ordered Apple to block or filter messages on iMessage that impersonate government agencies, requiring the company to implement new anti-spoofing protections by December as part of efforts to curb rising online scams, the Straits Times reports. Singapore's Ministry of Home Affairs (MHA) said that it had issued an Implementation Directive to Apple under the Online Criminal Harms...