The second iOS 26.4 developer beta renames the iOS bootloader.
The iOS bootloader just changed its first name, from “iBoot” to “mBoot”. Why, no one outside Apple Park knows yet.
While the second iOS 26.4 developer beta lets you test end-to-end encrypted RCS text messages with Android devices, the software contains another, more mysterious change.
Apple has changed the long-standing name of the iOS bootloader. It’s the first change since the operating system debuted nearly two decades ago.
More specifically, “iBoot” is now referred to as “mBoot”. The change came in the iOS 26.4 developer beta released on Monday.
The bootloader version number has also been changed so that it now starts at 18000. This is compared to the last version of iBoot in the first iOS 26.4 beta, which was 13822.
That’s a significant leap in version numbers, one that probably hasn’t been seen before. The meaning is not yet clear, but it is a large, unusual gap.
The new name “mBoot” can be seen through the so-called diff or detailed file comparison of the second and first developer betas of iOS 26.4. It is available on GitHub’s blacktop page.
AppleInsider has verified that the name “mBoot” is present in Monday’s iOS 26.4 developer beta. However, references to the new name are present in im4p files still labeled as “iBoot”.
Although beyond the scope of this article, the new bootloader name can be found if you have an Apple Silicon Mac running macOS 26.4 beta 2.
Apple hasn’t commented on the apparent change from “iBoot” to “mBoot” yet, and probably won’t. It remains unclear exactly what the change aims to achieve.
In short, it remains to be seen if the bootloader itself has undergone any significant architectural changes, or if it is just a new name.
But for iPhone end users, the rebranded bootloader will most likely not offer any visible or otherwise noticeable changes. This is because the iBoot subsystem effectively ensures an authenticated boot or initial load of iOS on the target device.
Crudely simplified, iBoot is there to boot the iPhone’s operating system whenever the device is turned on. The component is also used to verify the signature of the iOS kernel and perform other critical tasks related to loading iOS.
The new name “mBoot” could be a sign of upcoming hardware or software changes. Perhaps it has to do with the fact that Apple is expected to unveil at least five new products during its invite-only experience on March 4th.