Hide File Extensions not maintained since Sequoia 15.4 upgrade on M1 Mac mini and M3 MacBook Air

FWIW, they aren't hiding for me either.

Feel free to. send Apple a bug report.

Feedback - macOS - Apple

I noticed the same thing yesterday, and went through the usual steps as well with no luck. It has to be a bug. I'm fairly certain it will be corrected in one of the next few updates.

iJeffR wrote:

Ever since I have upgraded to Sequoia 15.4 on both my M1 Mac mini and my M3 MacBook Air, Finder is not hiding file extensions.

I have navigated to Finder > Preferences > Advanced and toggle the "Show all filename extensions" option to off on both machines. I have also done "Get Info" on the individual files and clicked, "Hide Extensions". Then, when I come back, the extensions are back. These files are in my iCloud Drive.

You are not alone 👍

The same behaviours and same steps were performed for files synced to iCloud

Numbers files were showing the .numbers extension, Pages with the pages extension, Keynote, QuickTime Player, TextEdit files all with appended extensions

Using a M3 MBA, M2 Mac Mini and M3 Mac Mini all with Sequoia 15.4

Each was updated on the day Off Release of 15.4, Mar 31, 2025

Theses behaviours only started after the installation of 15.4 and not before

The same behaviours and same steps were performed for files synced to iCloud

Today, April 7 and as I write this reply

Just checked again and the file extensions have since disappeared ( not showing )

You may give this some time to work itself out.

Maybe a couple of days to a week

It should not be that way but patience is a virtue

You are welcome and thank you too

As I have stated elsewhere today already, Finder is not in control of hiding file extensions other than by its Get Info panel. Depending upon how the application is written, it controls whether the file extension on saved/exported documents is shown or hidden. Presently, Apple's applications (probably not all but Pages and Numbers) are designed to show the extension. Depending upon how third-party applications are written, the same is true.

Being a UNIX operating system, macOS will behave differently than Windows or Linux distributions.

Personally, I can't find any files created by any app that have a hidden extension.

The Mac OS has never had an option to hide file extensions globally. You can choose to show all extensions in the Finder's settings, but not hide.

The Finder has never provided carte blanche default extension hiding. Not its role. Kurt Lang and I have stated our cases and we have been using macOS for decades. It is entirely the application designer's choice in the matter. Nothing is broken except your understanding of how this works.

The answer to the question is out there on the interwebs, but I'll share what worked for me. You need to be comfortable with the command-line, using the Terminal app (I recommend iTerm2, but I digress). There is a command called defaults that lets you make changes to the system defaults, without having to dig through app settings. It does come with its own learning curve, and you can always read about with man defaults in the terminal if you want to learn more about it.

The specific setting is the global attribute AppleShowAllExtensions, which should default to false. Unfortunately it seems to be getting stuck to true even if using the Finder's settings to change it. Since the attribute defaults to false, we can just "delete" it, which the Finder sees as "use the default." The command specifies the global context with the option "-g". Once the change is made you need to restart the Finder, which is what the killall command does; you should no longer see the extensions. Don't worry, the Finder automatically restarts.

defaults delete -g AppleShowAllExtensions && killall Finder

This has been bugging me for a while, finally realized that default was the answer, which I confirmed by a quick DuckDuck search to confirm I had the correct setting.

As a rule, I do not hide extensions. Several years ago, I wrote a voice-activated AppleScript solution that could hide or show a file extension on one or more selected files in the Finder. Got tired of talking to myself though.

Apple owns the operating system and the macOS team may have just decided in a vacuum to make the Finder retroactively show all hidden file extensions as a new macOS dogma. They could do that out-of-touch thing without an ounce of thought or remorse.

Been on all of the platforms you mention, for longer, and in developer, migration, and integrator roles. Lots of domestic and international travel thrown in to make things interesting.