Windows updates are supposed to make your PC faster, safer, and more stable. But sometimes, right after installing one, you notice something unexpected: your CPU suddenly shoots up, your fans spin like a mini jet engine, and Task Manager shows Microsoft Compatibility Telemetry (CompatTelRunner.exe) hogging resources.

So what's going on? Don't worry — your PC isn't breaking down, and nothing suspicious is happening in the background. This spike is actually normal, and here's the full story behind it.

What Exactly Is Microsoft Compatibility Telemetry?

Before we dive into the "why", let's tackle the "what".

Microsoft Compatibility Telemetry is a built-in Windows process that collects diagnostic data about how your system performs. It helps Microsoft understand:

Think of it as Windows doing a "big health check" after the operating system or apps have changed.

Why CPU Usage Spikes Right After a Windows Update

Windows updates often modify thousands of system files, drivers, registry entries, and service components. After such massive changes, telemetry has a lot of catching up to do. Here's what triggers the high CPU usage:

1. Re-Scanning the Entire System

An update refreshes many core system components. Telemetry then performs a deep rescan to understand:

This can temporarily spike CPU and disk usage because Windows is basically rebuilding its internal "performance map."

2. Checking Driver & Hardware Compatibility

After any update, Windows wants to ensure your:

all still work smoothly.

This compatibility check directly involves the Telemetry process, which explains why a new NVMe or GPU update can also intensify the scan.

3. Update Success & Health Validation

Windows uses telemetry to confirm whether the update:

These validations are essential because they help Microsoft fix bugs faster in future updates.

4. Updating Machine Learning Profiles

Some Windows features rely on local ML models (startup prediction, service optimization, energy profiles). After an update, these models retrain using new data.

Telemetry feeds these models, which again leads to a burst of CPU activity.

5. Windows Search Index Rebuilding

This one surprises many users.

After updates, Windows Search often rebuilds its index, especially if Explorer, Start Menu, or the Search UI was updated. Telemetry queries the indexer to ensure the search experience remains accurate.

If you have:

this indexing can take a while.

How Long Does the High CPU Last?

Most of the time:

Your upgraded Gen4 NVMe (which is fast) makes Windows run even more background tasks aggressively, so the CPU spike might feel more "active" compared to slower drives.

When You Should Start Worrying

Telemetry usage becomes suspicious only when:

In these cases, it may point to corruption or misconfigurations.

How to Calm Telemetry Down (Without Disabling It)

You don't have to turn telemetry off — Windows relies on it heavily. Instead, these steps usually tame the spike:

Restart the Diagnostics Tracking Service

Run as Administrator:

sc stop diagtrack
sc start diagtrack
 

Rebuild the Windows Search Index 

Settings → Search → Searching Windows → Advanced → Rebuild Index 

Clean & Repair System Files

DISM /Online /Cleanup-Image /RestoreHealth
sfc /scannow
 

Manually Trigger .NET Runtime Optimization

C:\Windows\Microsoft.NET\Framework64\v4.0.30319\ngen.exe executequeueditems
 

Update Drivers (Especially for Surface Pro)

Surface firmware updates often resolve telemetry-related background spikes.

Final Thoughts

High CPU usage from Microsoft Compatibility Telemetry right after a Windows update may look scary, but it's almost always completely normal. Windows is simply re-learning your system, validating new components, and updating its performance baseline. Once the post-update housekeeping is done, everything settles back down.

If you ever want help checking what exactly is causing your spike — like reading Event Viewer logs or identifying specific telemetry tasks — just let me know.