Upgrading Unity Projects Using a Clean Project Migration

Introduction

Unity upgrades are rarely risk-free. Over time, projects accumulate legacy settings, deprecated APIs, obsolete packages, and serialized data that no longer behaves correctly in newer versions of the engine.

While Unity Hub allows direct project upgrades, experienced teams often avoid this approach for anything beyond minor patch updates. Instead, they favor a clean migration strategy, which minimizes technical debt and exposes compatibility issues early.

What Is Clean Project Migration?

Clean Project Migration is the process of:

1. Creating a new Unity project in the target engine version
2. Installing and configuring required packages and systems first
3. Rebuilding or selectively migrating project settings
4. Copying project assets into the clean environment
5. Fixing issues and validating behavior through testing

Rather than forcing Unity to reinterpret years of legacy data, this approach lets you reintroduce only what you actually need.

Why This Technique Works

1. Eliminates Legacy Configuration

Unity serializes many settings in version-specific formats. Old graphics, physics, or input settings may technically load in a newer editor but behave incorrectly.

Starting from a clean project ensures:

• Correct default values for the new engine version
• No hidden, outdated configuration data
• Predictable behavior across platforms

2. Forces Explicit Dependency Management

By installing packages first, the team must:

• Identify all real dependencies
• Choose compatible versions intentionally
• Avoid Unity auto-installing deprecated or incompatible packages

This significantly reduces “package rot” and dependency conflicts.

3. Improves Long-Term Stability

Teams that use clean migration consistently report:

• Fewer editor crashes
• Fewer serialization issues
• Cleaner version control diffs
• Easier onboarding for new developers

When to Use Clean Project Migration

Recommended scenarios:

• Upgrading between LTS versions
• Skipping multiple Unity versions
• Switching render pipelines (Built-in → URP/HDRP)
• Projects older than ~2 years
• Projects with complex package dependencies

Not recommended for:

• Minor patch upgrades
• Late-stage production near release
• Live service games without full regression testing

Step-by-Step Migration Process

Step 1: Create a New Project

Create a new Unity project using:

• The target Unity version (LTS)
• The same template (URP, HDRP, 2D, etc.)
• The same build targets as the original project

This project becomes your clean baseline.

Step 2: Install Required Packages First

Before importing any assets:

• Install all required packages via Package Manager
• Match versions from the original project’s manifest.json
• Avoid using “latest” unless intentional

Best practice: Copy the original project’s:

Packages/manifest.json
Packages/packages-lock.json

into the new project and let Unity resolve dependencies.

Step 3: Configure Core Systems

Set up foundational systems before adding assets:

• Input System (bindings, actions)
• Render Pipeline assets (URP/HDRP)
• Addressables (if used)
• Netcode / Multiplayer configuration
• Localization systems

This ensures assets import into a correctly configured environment.

Step 4: Migrate Assets

Copy the entire:

Assets/

folder into the new project.

Unity will reimport assets using the new engine version and package stack. Expect long import times and compiler errors at this stage.

Step 5: Selectively Migrate Project Settings

Do not blindly copy the entire ProjectSettings folder.

Instead, selectively migrate only what’s necessary:

Commonly migrated files:

• TagManager.asset (Tags & Layers)
• GraphicsSettings.asset
• QualitySettings.asset
• Physics*.asset
• Input-related settings (if using legacy systems)

Settings often safer to rebuild:

• Editor preferences
• Build settings
• Platform-specific overrides

Step 6: Resolve Errors and Warnings

Address issues in this order:

1. Compilation errors
2. Package incompatibilities
3. Deprecated API usage
4. Serialization warnings

Avoid suppressing warnings unless fully understood.

Step 7: Validate the Project

Treat migration like a release candidate:

• Load all scenes
• Run gameplay flows
• Test save/load
• Verify UI navigation
• Check physics and animation behavior
• Build and run on all target platforms

Automated tests should be run if available.

Common Mistakes to Avoid

• Copying only the Assets folder without settings
• Letting Unity auto-upgrade packages blindly
• Migrating settings without understanding them
• Upgrading mid-feature development
• Skipping regression testing

Conclusion

Clean Project Migration is not the fastest way to upgrade a Unity project—but it is often the safest and most professional.

By rebuilding the project foundation first and migrating assets deliberately, teams gain:

• Stability
• Predictability
• Long-term maintainability

For large or long-lived Unity projects, this technique is often the difference between a smooth upgrade and months of hidden technical debt.