Prospira Tweaks
The criticism quoted most often, that the system is left bare because Windows Defender was stripped out of it, stopped being true at version 0.3.1. Defender is an optional component today and it is on by default. The same goes for UAC, the prompt asking for administrator consent: it came back, and it is on by default too.
We start there because it is hard to decide whether something is worth installing when half the available opinions describe something other than what you will actually download.
What AtlasOS actually is
A modification of Windows 11, not a separate operating system.
You install it the way you install Windows, from an image, and during the install it disables and removes part of the system. Its authors call it a lightweight modification of Windows, designed for enthusiasts.
It is free and open. The code sits on GitHub, so anyone can read what it does. The project is maintained: version 0.5.0 shipped in October 2025.
The part that is easy to miss: this is not a set of switches you flip after installing. It is a system image. You make the decision once, before installing, for the whole machine.
Is AtlasOS safe?
Yes, in the sense of security patches. It skips feature updates, and that is the part worth understanding.
Their documentation says plainly that the system applies security patches and cumulative updates. You are not left unpatched.
There is a second sentence right next to it, and that is the one that matters:
Feature updates skipped to preserve optimizations.
Feature updates are the large, versioned ones that move Windows onto a new release once a year. AtlasOS does not install them, because each one would undo part of what it changed.
In practice that means you stay on the Windows release you installed Atlas on. Security patches arrive. New features, drivers that need a newer release, and whatever Microsoft ships in the big updates do not. When you do want to move to a newer release, you install from scratch.
A separate thing worth understanding: you are installing an image prepared by someone else. The code is public, but the file you download does not come from Microsoft. For some people that is a non-issue and for others it settles the question. It is worth deciding on purpose rather than in passing.
What it removes
One thing permanently. Everything else is either disabled or can be reinstalled.
Their documentation splits the changes into three groups.
Removed permanently. There is one item here and it is worth knowing: Smart App Control. The documentation is blunt about it: once it is disabled you cannot reinstall it, and getting it back means reinstalling Windows.
Disabled, but you can switch them back on. Telemetry, error reporting, Microsoft account syncing, advertisements and system tips, activity history, and the less-used context menu entries.
Applications uninstalled, and restorable. Internet Explorer, OneDrive (kept if you already use it, so nothing is lost), Edge as an option, Steps Recorder, the legacy Windows Media Player, Maths Recognizer, and a set of Store apps including Teams, Mail, Calendar, Cortana and Xbox Companion.
Most of that comes back as an optional feature. Only the one item above is gone for good.
Windows 10 or Windows 11?
Windows 11. That is what the project officially supports.
This question comes up in search constantly and the answer is short: their own site states that AtlasOS officially supports Windows 11.
Older builds for Windows 10 circulate, along with files on download portals, but they are not what the project maintains today. If you are on Windows 10 and looking at AtlasOS, the real choice is between installing Windows 11 first or hunting for an unmaintained build. The first is the sensible one.
Anticheat, CS2 and Valorant
AtlasOS says it supports all of them. We will not make that promise about our own tool, and it is worth explaining why.
Their FAQ answers this confidently, saying Atlas is the same as standard Windows and supports all functionality and all anti-cheats.
We have no grounds to dispute that and we are not going to. But here is what we say about our own software in the same situation, because it sounds different and we think it is the more useful answer.
We will not give you a guarantee. No anticheat vendor, not VAC, not Vanguard, not Ricochet, not FACEIT, not ESEA, certifies third-party tools. Nobody can promise something they do not control. What we can do is tell you exactly what gets changed, and we do.
If you play a title with a strict anticheat and the machine is your ranked machine, treat every confident reassurance with some reserve, ours included, and base the decision on what you would lose.
What cannot be undone
Reinstalling Windows is the only way back, and AtlasOS says so itself.
This is the thing to know before installing, because afterwards it is too late. Quoting their own FAQ:
AtlasOS does not provide a rollback or recovery option. You will need to reinstall Windows, just the same as you would need to reinstall Windows to install AtlasOS.
That is honestly written and it deserves credit for sitting openly in the documentation. But it means exactly what it says: the only route back is a fresh install of Windows. There is no switch, no uninstaller, no restore point from before.
If a week later you decide one particular change bothers you, the choice is between living with it and rebuilding the machine.
When AtlasOS is the right choice
Four situations where it is the right answer and paying anyone would be a waste.
You are doing a clean install anyway. New drive, new build, or a reinstall you had already planned. If you are rebuilding regardless, the cost of entry disappears.
Reinstalling Windows does not scare you. You have done it, your files are backed up, you know where the drivers are. Then the lack of a way back is an inconvenience rather than a risk.
You want the system stripped as far as it goes, and accept what that costs. Atlas can go further than any tool working on a running system, because it makes its changes during installation.
The machine is only for games. No work on it, no company documents, no software that simply has to keep working.
In those four cases, take AtlasOS. It is free, it is maintained, and you can read the code.
When it is not
One machine you also work on, or any case where you want to undo a single change.
You have one computer and you work on it. The risk of something breaking on a Wednesday morning outweighs a few frames.
You do not want to rebuild the machine. That is the entry condition, not an option.
You care about one specific change. If one thing in Windows bothers you, installing a whole system image to fix it is replacing the engine to clear a dashboard light.
The computer is shared. Somebody else works on it, studies on it, or simply expects everything to be where it was.
You want to be able to change your mind. The same point as above, worth repeating, because it is usually the one that decides it.
How our approach differs
One decision for the whole machine, against a series of small ones on the Windows you already have.
We are not going to claim we are faster, because that cannot be proven honestly. This market quotes three different figures for the same change and discredits itself doing it. The difference is elsewhere.
AtlasOS is one decision, made once, for the whole machine. Our application is a series of small decisions on the Windows you already run. We do not replace the installation image, and there is no step where you rebuild the machine.
Specifically, and only what we can point to in our own code:
We turn System Restore on rather than off. The application re-enables system restore if it was disabled, and lets you save a restore point before you start.
Scheduled tasks are disabled, not deleted. The difference is that a disabled task can be switched back on. The filter deliberately skips Defender, Windows Update and the update orchestrator, because those are not things to sweep up in bulk.
You see every change before you turn it on. Each card says what it does and what it risks, and live CPU and GPU temperatures show whether anything actually changed on your machine, not in a screenshot from somebody with different hardware.
And one thing a system image cannot reach by definition: the BIOS. Motherboard settings sit outside anything happening at the Windows level.