GAMMA is a free fan modpack. It runs on S.T.A.L.K.E.R. Anomaly. The GOG one-click version needs you to own a base game.

How much space does GAMMA need?

The wiki lists at least 150 GB free and says 175 to 200 GB is safer. The installed size is roughly 130 GB.

Which Anomaly version do I need?

The wiki install guide uses Anomaly 1.5.3 with GAMMA RC3. Always check the wiki for the current version.

Does GAMMA work on Linux?

There are separate guides and a gamma-launcher tool. Reports say the GOG one-click version does not work on Linux.

How to Install STALKER GAMMA: Step by Step Guide

G.A.M.M.A. is a free modpack for S.T.A.L.K.E.R. Anomaly that makes the game harder and more focused on survival. It is big, so a careful install saves hours. This guide follows the official GAMMA wiki for Windows and was checked on October 13, 2026. Instructions can change, so check the wiki and the community Discord for the newest version. GAMMA is a fan project and not an official product of GSC Game World.

Key takeaways

You need Anomaly 1.5.3 and the GAMMA RC3 archive, and the official wiki lists at least 150 GB of free space (175 to 200 GB is safer).
Use 7-Zip, and put the Anomaly and GAMMA folders on the same internal drive, outside Program Files, Documents, Desktop and OneDrive.
Add both folders to your antivirus exclusions first.
GOG offers a one-click GAMMA install, which needs you to own a base game.

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What you need before you start

Windows 64-bit. Other systems have their own guides.
7-Zip. WinRAR and the default Windows tool can fail on very large .7z files.
.NET Framework 3.5, the latest DirectX and the latest 64-bit Visual C++ Redistributable.
Large downloads: about 9 GB for Anomaly, 11 GB for GAMMA RC3 and 27 GB of mods. The installed size is roughly 130 GB.

Step by step

Download the Anomaly 1.5.3 archive and one mirror of the GAMMA RC3 archive from the wiki links.
Create two separate folders, one for Anomaly and one for GAMMA. They must be on the same internal drive and not inside each other.
Add both folders to your antivirus exclusions before you download or extract.
Extract Anomaly 1.5.3 into the Anomaly folder with 7-Zip.
Run AnomalyLauncher.exe, click Play until the main menu appears, then exit.
Extract the GAMMA RC3 archive into the GAMMA folder.
Open the folder called Grok's Modpack Installer and run G.A.M.M.A. Launcher.exe. The wiki says the launcher should show version 8.6. If not, update it first.
Click First Install Initialization. You need this only once.
When Mod Organizer 2 asks for the game, choose your Anomaly folder, then close it.
Leave the options at default and click Install / Update GAMMA. Wait for Installation finished.
Click Play, choose Anomaly (DX11) in Mod Organizer 2 and click Run.

The GOG one-click option

GOG added GAMMA as a one-click mod install in December 2025. A reader comment quoted the store page and said it requires owning S.T.A.L.K.E.R. 2 (Standard Edition) or Call of Pripyat (Enhanced Edition). Check the GOG page yourself. Reports say the GOG version does not work on Linux, where players use the gamma-launcher tool or a community guide.

Common mistakes

Antivirus blocks: Norton, Avast, AVG, Malwarebytes and Bitdefender can block the installer or Mod Organizer 2. Add exclusions or turn protection off only while installing, and turn it on again.
Wrong folders: installing in Program Files, Documents, Desktop or OneDrive causes permission problems.
Not enough space: plan for 175 to 200 GB. Deleting the archives in the downloads folder saves about 20 GB, but repairs need them again.
Installing over an old version: ModDB says not to install Anomaly over older versions.