Apple may have tested its most powerful chip, the M3 Ultra, in MacBook Pro models before deciding not to bring them to market. A recent leak from an internal iOS 18 build, discovered on a Chinese engineering prototype iPhone 16, includes references to unreleased 14-inch and 16-inch MacBook Pros with codenames “J514d” and “J516d”—designations believed to correspond to models equipped with the M3 Ultra chip.
These references were found in a diagnostics test folder within the internal iOS build, suggesting Apple ran performance and stability tests on these prototypes. The M3 Ultra, currently exclusive to the Mac Studio, features up to a 32-core CPU, an 80-core GPU, and supports up to 512GB of unified memory. By contrast, the MacBook Pro lineup maxes out with the M4 Max, which supports a 16-core CPU, 40-core GPU, and up to 128GB of unified memory.
Why Apple Likely Canceled the M3 Ultra MacBook Pro
Thermal and power limitations likely prevented Apple from releasing a MacBook Pro with the M3 Ultra. While the chip offers significant performance gains, it has a high thermal design power (TDP) rating—reportedly around 140W. That’s nearly double the M2 Max’s 79W. Even though the M3 Ultra’s power efficiency is improved, the thermal load would exceed what the current MacBook Pro chassis can handle.
Apple faced similar challenges in the past. The PowerBook G5 was scrapped due to thermal issues, and internal testing of M1 Pro and M1 Max chips in the Mac mini also never led to a product release. These prototypes often reach advanced stages of development but are shelved when they don’t meet the company’s standards for efficiency and real-world use.
Prototype Leak Offers Glimpse Into Apple’s Internal Testing
According to a Bilibili post by a user who analyzed the iOS 18 test files, Apple engineers used a script labeled run_murphy_g17x.sh to evaluate GPU performance under various loads and data types. That script included the J514d and J516d identifiers, following Apple’s internal naming pattern where a “d” suffix refers to models equipped with Ultra chips.
The leaker also noted Apple may have explored offering 512GB of unified memory as a differentiator for MacBook Pro models powered by the M3 Ultra. This suggests the company considered an Ultra-powered MacBook Pro in response to increasing demands around AI workloads and competition in high-performance laptops.
As reported on Bilibili, this level of prototyping is not unusual. Apple often tests hardware combinations that never ship. The M1 Max Mac mini and a canceled A9 iPad mini were both uncovered through similar internal file analysis, yet never made it to market.
Apple has not commented on the leak. For now, the M3 Ultra remains exclusive to desktop-class machines like the Mac Studio.