Increased System Data after macOS 27.0.1 upgrade

What you are seeing is expected, and is the new normal. You do not need to take any action.

"System Data" comprises your data, but they are typically hidden files that Spotlight cannot assign to a specific category like Documents or Applications. Examples include Outlook attachments, iOS updates, Cloud storage caches, etc. Starting with macOS 27 Golden Gate, System Data also includes what macOS used to call ‘purgeable’ storage – system caches, Time Machine snapshots and some other data, though the user had no control over the purging.

On macOS 27, separate ‘purgeable’ space is no longer reported, and instead those data are now considered as used space. They are also now included in System Data, accounting for the apparent increase you (and others) have noticed. You didn't lose space, macOS just categorizes things differently now than on Tahoe.

More detail on this change in this User Tip:

System Data and Free Space Changes in Gol… - Apple Community

The best advice is to just ignore the System Data category. ‘System Data’ is merely a catch-all category for files that Spotlight cannot assign to specific categories like Applications, Documents, Photos, etc. In fact, what is now shown as System Data used to be reported as ‘Other’, Apple changed the label in macOS 12 Monterey. System Data probably sounds better, but Other was closer to reality. 

RamikK wrote:

I’m wondering if this is normal or if I should be concerned. System Data has ballooned after the upgrade…

100% normal.

Here’s what Storage reports:

That display is wildly inaccurate. Don't even go there. It will just confuse you.

I know macOS 27 introduced Apple Intelligence, but 44GB of System Data seems like a lot, especially right after an OS upgrade.

Did I mention being confused. Note that "System Data" has absolutely nothing to do with system data. Make sense? I hope not.

Is this expected behavior immediately after upgrading?

Absolutely.

Could it be temporary stuff like caches, indexing, or post-install cleanup that will settle down over the next few days? Or is this just the new normal with macOS 27?

This is the new normal. Don't try to download any "clean up" tools. They will only cause problems.

Thanks to everyone who replied! Just to make sure I understand correctly: on macOS 15.8, did I effectively have more free space only “on paper” in the Storage settings? In other words, was that extra 60+ GB already occupied by purgeable data, but simply not shown as used in the storage bar? And now, in macOS 27.0.1, is that space finally being counted as used and displayed under System Data?

neuroanatomist wrote:

On macOS 27, separate ‘purgeable’ space is no longer reported, and instead those data are now considered as used space.

FWIW on my MBP M5 macOS 27.0.1 I first did see 'purgeable' and then a few hours later during the same boot session after doing some Safari and LibreOffice work with some slightly edited .ods document it had vanished just as I was about to reboot and check if it was still there:

RamikK wrote:

on macOS 15.8, did I effectively have more free space only “on paper” in the Storage settings?

Yes. This has been a problem for several years. Most people only notice it when they run out of free storage and the system refuses to download a system update. Because the whole world is addicted to those system updates, they positively freak out when that happens. They aren't concerned about their data being corrupted. It's the update from Apple that they value so much.

In other words, was that extra 60+ GB already occupied by purgeable data, but simply not shown as used in the storage bar?

Don't attempt to rationalize or figure out how Apple calculates these things. No one outside Apple can possibly know that. And after a few exchanges with people who are inside Apple, you start to realize that they don't understand it any better.

And now, in macOS 27.0.1, is that space finally being counted as used and displayed under System Data?

No! System Data doesn't exist. It's a fantasy. Don't look at the display that shows it to you. It's like those people years ago that believed soap operas were real. It is possible to have the operating system tell you material values like used and free storage, but it's pretty difficult to find out where to do that. It usually involves the command line. Most of the pretty displays range from sleight of hand to outright fantasy. Don't be fooled by the 3 gigabyte monte.

Matti Haveri wrote:

FWIW on my MBP M5 macOS 27.0.1 I first did see 'purgeable' and then a few hours later during the same boot session after doing some Safari and LibreOffice work with some slightly edited .ods document it had vanished just as I was about to reboot and check if it was still there:

That's why I caution people about trying to replicate Apple's math or explain how it works. But it's all just a fantasy.