2025 MacBook Air restarts after opening lid while computer is on

The Mac doesn't typically restart silently.

This sounds more like the computer is simply logging you out from your user account after inactivity.

You can address this at System Settings... > Privacy & Security. Scroll to the bottom and click the Advanced... button. There you can disable the 'Log out automatically after inactivity' feature, or change the inactivity interval.

mpoinar wrote:

In the 3 weeks since I bought this, twice when I shut the lid and then opened it, it had restarted. Both times I only had shut it for a short time, then reopened the lid. Upon reopening, the screen was black and immediately it silently restarted - both times. I have my sound turned on but there was no sound.

What can be done so that it doesn't do this anymore? Are there settings anywhere to stop this?

First thing is you need to confirm it actually restarted and why it restarted. This is not always easy to do. It sounds like the system is having a Kernel Panic.

Usually problems like this will be related to issues with third party software. Run the third party app EtreCheck and post the complete report here so we an examine it for possible clues.

How to use the Add Text Feature When Posting an EtreCheck Report - Apple Community

The other reason is due to possible hardware issues. Disconnect all external devices just in case one of them is causing a problem.

Yes, that's exactly what I meant.

Since that is already off, one other thing comes to mind and that's automatic updates.

If you have your Mac set to automatically install software and/or macOS updates, it may be that the restarts are triggered by that action. Generally speaking, it's probably best to allow updates to install automatically, but obviously the choice is yours to make.

Check this at System Settings > General > Software Update > Automatic Updates.

There you can choose whether to download only or download and install macOS updates, application updates and/or Security Responses.

mpoinar wrote:

[...]

And will this prevent the mac from shutting down and restarting when I open the lid?

No, this won't address the shut downs at all, only the auto-start when opening the lid.

At this point I'm out of ideas as to why it is shutting down.

Under normal circumstances, shutting down is not supposed to happen simply by closing the lid of the computer. It also is not default behavior for a Mac to be silent when it reboots, though that startup chime can be silenced in System Settings. It's this particular detail that suggests to me that the Mac is simply logging you out of your user account.

A reboot would typically be accompanied by the startup chime, then the login screen would appear, and when you've logged in again your apps and previously open windows would reopen, if that is your preference.

When you log out your user but do not shut down the Mac, your applications windows are closed and the apps are quit. If you close the lid after logging out, then the screen obviously goes dark. Now when you open the lid, the Mac only has to present the login screen so there is no chime. Then after you log in, all of your apps and their windows would have to reopen, just as if you had restarted.

You can observe this behavior yourself by selecting Apple menu  > Log Out (User)... and then let the timer run out.

I would suggest running the third party app EtreCheck and posting the complete report here so we can examine it for possible clues.

How to use the Add Text Feature When Posting an EtreCheck Report- Apple Community

Also, if you have not already done so, disconnect all external devices from the laptop prior to closing the lid just in case one of those devices is causing the problem.

You are aware that the latest MacBook computers do automatically start just by lifting the lid, yes?

It's a 'feature'.

This activity can be prevented by using a specific Terminal command.

Prevent a Mac laptop from turning on when opening its lid or connecting to power - Apple Support

mpoinar wrote:

I never log out though. And I don't have to log in either. So I am not sure about what you are saying. Would it help if I disabled sleep in the terminal?

Disabling sleep isn't a bad idea, and yes, it might help.

Sleep functions have been know to cause problems for some, on the Mac mini especially.

Sounds like you have automatic login enabled.