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📦 Update Slipstreaming

How Do You Put the Latest Windows Updates Inside the ISO, So a Fresh Install Is Already Up to Date

Install Windows, then lose an hour to "Checking for updates". Slipstreaming bakes the current cumulative update into the image itself — the PC lands on the desktop already patched.

✍️ Technical Anshu🪟 Windows 10 / 11⏱️ 7 minute read
🎥 The full custom ISO build this update step belongs to — watch it on video

Microsoft's downloadable ISO is always months behind the current patch level, so every fresh install repeats the same ritual: install, connect, download a gigabyte of cumulative updates, restart, repeat. Slipstreaming means integrating those update packages into the offline image before building the ISO. It is official, supported servicing — the same DISM machinery Windows Update itself uses — and on a custom ISO it pairs naturally with debloating and driver integration. You need the correct update files: download the latest Cumulative Update (.msu) for your exact Windows build from the Microsoft Update Catalog, plus the matching .NET update if you want it.

Settings — Windows Update, on a fresh stock install

Updates available

Cumulative Update for Windows 11 (x64-based Systems)Downloading...
.NET Framework Cumulative UpdatePending download
Windows Security platform updatePending download
...followed by a restart, then more updates~1 hour lost
Day one with a stock ISO: a queue of downloads and restarts before the PC is usable. Slipstreaming empties this queue in advance.
1

Get the Right Update Packages

  1. Find your ISO's build number (mount or check the release notes) — a cumulative update only applies to its own Windows version and architecture
  2. Open the Microsoft Update Catalog and download the latest Cumulative Update MSU for that build (x64 for 64-bit images)
  3. Put the packages in a plain folder, e.g. C:\Updates — if a separate Servicing Stack Update (SSU) is listed for your build, download it too
2

Mount the Image and Add the Packages with DISM

Open Command Prompt as Administrator:

  1. dism /Mount-Image /ImageFile:"C:\ISO\sources\install.wim" /Index:1 /MountDir:"C:\Mount"
  2. Add the updates — point DISM at the folder and it processes the packages in the right order:
  3. dism /Image:"C:\Mount" /Add-Package /PackagePath:"C:\Updates"
  4. Watch the output: every package should report "The operation completed successfully". A package meant for a different build will be rejected — that message is information, not damage
Administrator: Command Prompt — DISM Add-Package

Deployment Image Servicing and Management tool

Processing 1 of 1 — Adding package ...

[==========================100.0%==========================]

The operation completed successfully.

DISM integrating an update package into the mounted image — this is what success looks like before you even build the ISO.
3

While You Are Here: Enable .NET Framework 3.5 Offline

Older but common software still asks for .NET 3.5, and enabling it later needs the internet. Offline, it comes from the ISO's own files:

  1. With the image still mounted, run (D: is the drive/folder holding your extracted ISO's sources\sxs):
  2. dism /Image:"C:\Mount" /Enable-Feature /FeatureName:NetFx3 /All /Source:"C:\ISO\sources\sxs" /LimitAccess
  3. Now every install from this ISO has .NET 3.5 ready from the first boot
4

Clean Up, Save, and Verify

  1. Shrink the component store before saving (optional but worthwhile after several packages): dism /Image:"C:\Mount" /Cleanup-Image /StartComponentCleanup
  2. Save the image: dism /Unmount-Image /MountDir:"C:\Mount" /Commit
  3. NTLite users can skip the commands: the Updates page adds the same MSU files to the queue and applies them during processing
  4. Test the rebuilt ISO in a virtual machine and check Settings → Windows Update history — the slipstreamed build should show as the installed patch level from day one
⚠️ Two honest warnings: (1) The /ResetBase cleanup variant makes the integrated updates permanent — they can never be uninstalled afterwards, so only use it on a build you have tested. (2) An outdated ISO refreshed this way is current only on the day you build it; slipstreaming is a habit to repeat every few months, not a one-time cure.

🎥 The Complete Custom ISO Build on Video

Debloat, drivers, configuration and the final ISO — the whole workflow this update step fits into, shown live.

▶️ Watch Full Video
❓ Frequently Asked Questions (FAQ)

Do I need to install updates in a specific order?

When you point DISM's Add-Package at a folder, it evaluates dependencies and applies packages in the correct order, including a servicing stack update when one is present. Modern cumulative updates often bundle their own SSU, which is why a single current LCU is usually all you need.

Can I slipstream updates into install.esd directly?

No. ESD files are a distribution format, not a servicing format — convert install.esd to install.wim first (DISM Export-Image), service the WIM, and only convert back to ESD at the end if you need the smaller file size.

How much bigger does the ISO get after slipstreaming?

Typically a few hundred MB to around 1 GB for a cumulative update, because the new components replace old ones rather than simply adding on top. Running the component cleanup before saving keeps the growth under control.

This guide is based on the Technical Anshu video on creating your own custom Windows ISO • Stuck on a step? Ask in the video comments — you will get help 🙏