Today, Apple will release macOS High Sierra 10.13.6 Supplemental Update—an update the company says will fix the widely reported performance throttling problem with the new 2018 MacBook Pro.

Since the device's launch about a week ago, some users reported that sustained, heavy utilization of both the CPU and the GPU caused the 15-inch MacBook Pro's Intel Core i9 processor to drop below its base clock frequency, negatively impacting performance for some demanding workloads.

Apple says this was a firmware issue introduced after the company did its own internal benchmarks but before the device made it into consumers' hands. Here is the statement from an Apple spokesperson on the issue and the firmware update meant to resolve it:

Following extensive performance testing under numerous workloads, we've identified that there is a missing digital key in the firmware that impacts the thermal management system and could drive clock speeds down under heavy thermal loads on the new MacBook Pro. A bug fix is included in today's macOS High Sierra 10.13.6 Supplemental Update and is recommended. We apologize to any customer who has experienced less than optimal performance on their new systems. Customers can expect the new 15-inch MacBook Pro to be up to 70% faster, and the 13-inch MacBook Pro with Touch Bar to be up to 2X faster, as shown in the performance results on our website.

Once we've installed the new firmware, we will run a series of benchmarks and update our main review with a revised recommendation (look for that by the end of this week).

Update: We re-tested the MacBook Pro and shared our results. The update fixed the problem for the most part, but there is still some throttling in extreme edge cases.

What happened

The first report came from a video by gadget YouTuber Dave Lee . Based on tests with Adobe Premiere, he claimed that the Core i9 CPU in the new MacBook Pro was throttling to a degree that it was outperformed by a 2017 MacBook Pro. He concluded that the CPU was too much for the MacBook Pro's thermal management system to handle.

AppleInsider and some others chimed in to agree, while other publications and YouTube personalities shared conflicting benchmarks suggesting the problem was not as severe as initially claimed.

There were some problems with the reports we saw this week, though. First, Lee used Adobe Premiere to do his testing, but any Mac video editor will tell you that Adobe Premiere is not ideally optimized on Macs. The next widely circulated report came from AppleInsider, which demonstrated notable CPU throttling on the MacBook Pro's Core i9 by running several Cinebench R15 benchmarks in rapid succession. However, The Verge editor Dieter Bohn reached out to the company behind Cinebench (which also makes 3D modeling software Cinema 4D) to ask whether we can expect the software to accurately measure performance on this hardware. He got this response back:

Cinema 4D is compatible and optimized to utilize all these chips have to offer. Unfortunately, our Cinebench application has not been upgraded to measure the performance in a meaningful way. The development team is aware and will be addressing this in the future.

Geekbench developer John Poole got his hands on both the Core i7 and Core i9 configurations, and he tweeted that he was running benchmarks that showed the Core i9 running more slowly than the Core i7 in some situations. Poole did see consistently superior performance from the i9 in single-core tests.

It's often difficult to benchmark a product that has just hit the market accurately, but in this case, there was more going on than usual.

What we found

We held off on covering the initial reports so we could make sure we tested the issue ourselves in the course of preparing our review. We also hoped to talk to Apple about it.

We did find that something odd was happening when testing, though. Many benchmarks like Geekbench test short bursts of performance, and those showed performance more or less in line with expectations. But heavy-duty tasks that hit both the GPU and CPU continually over a period of time—like repeatedly running both CPU and GPU benchmarks simultaneously for several minutes straight, or running numerous ongoing Xcode simulations while also rendering a large 4K video in Final Cut—showed not just marked drops in overall performance, but also wildly fluctuating clock speeds.

Below are the results of some of our tests comparing a 2016 MacBook Pro and our review unit of the 2018 MacBook Pro.

Samuel Axon



Samuel Axon

Samuel Axon

Samuel Axon

Samuel Axon

That's not normal, and it's not something I would expect to see from Apple. Worse yet, while reports on YouTube and social media claimed that it only affected the Intel Core i9 configuration, we have since learned that it affects all 2018 MacBook Pros.

Initial reports suggested that this issue was due to a fundamental limitation of the MacBook Pro's chassis—that tapping the full performance of Intel's latest processors would not be possible without a redesign of these computers, at least until Intel brings these high-end chips down to 10nm. But it seemed unlikely that Apple was deliberately shipping a hampered product and hoping no one would notice.

What’s next

In fact, it looks like Apple was initially as baffled as the users who encountered this throttling issue. Earlier this week, the company talked to members of the press and influencers (Ars included) who encountered the throttling to try and replicate their workloads and identify what was happening. The firmware issue was introduced into the mix after Apple performed its own internal tests to assess performance and the efficiency of the CPU and the thermal management system.

Apple succeeded in replicating some of those workloads, like the one described in Dave Lee's video, and the company measured improved performance after the new firmware update.

However, we remain eager to test this ourselves. It's possible that the firmware update will markedly improve performance as Apple has promised but that the MacBook Pro's thermal management system will still not be up to the task of drawing optimal performance from the Core i9 CPU in particular. While the i9-8950HK in the 15-inch model's top configuration has the same Thermal Design Point (TDP) as the i7-8850H one step down, the latter has a configurable TDP down of 35W, and the i9 doesn't. Further, a max turbo frequency of 4.8GHz is aggressive. When Apple first designed this chassis, Intel was likely telling the company that this generation of CPUs would be down to 10nm, but that did not turn out to be the case. The verdict is not in yet.

We're hoping for strong, mostly consistent performance after the firmware update, but we still don't know for sure whether this MacBook Pro design can fully accommodate that CPU. In any case, we'll certainly share our findings later this week.