ModelImporter APIs removed in Unity 6.5: isFileScaleUsed, optimizeMesh and more

Unity 6.5 turned long-obsolete ModelImporter properties into compile errors. The replacement for isFileScaleUsed, normalImportMode, optimizeMesh and resampleRotations.

Status
Removed or stopped working in Unity 6.5 · Editor
Old
isFileScaleUsed, normalImportMode, optimizeMesh, resampleRotations
New
useFileScale, importNormals, optimizeMeshPolygons / optimizeMeshVertices, resampleCurves
Checked
2026-10-05, against the sources below

What changed

Editor scripts that configure model imports, usually an AssetPostprocessor, can stop compiling in Unity 6.5. Properties that had been obsolete with warnings for a long time now cause compile errors.

Unity's API Updater handles most of them; the rest follow the mapping below. optimizeMesh has no single replacement: set optimizeMeshPolygons and optimizeMeshVertices to choose which optimizations you want.

Before and after

Before
C# 
void OnPreprocessModel()
{
    var importer = (ModelImporter)assetImporter;
    importer.isFileScaleUsed = true;
    importer.optimizeMesh = true;
}
6 lines
After
C# 
void OnPreprocessModel()
{
    var importer = (ModelImporter)assetImporter;
    importer.useFileScale = true;
    importer.optimizeMeshPolygons = true;
    importer.optimizeMeshVertices = true;
}
7 lines

Fix it automatically

Paste a script into the Unity 6 Script Upgrade Checker and it applies this rename for you, along with the other safe fixes for your target version.

Open this example in the checker

Questions

Do these removals affect my game build?
Only indirectly. ModelImporter is Editor-only, so these properties appear in Editor scripts such as AssetPostprocessors. But a compile error in any Editor script stops you entering Play mode and building until it is fixed; see All compiler errors have to be fixed.
Will Unity rewrite the code for me?
Unity's API Updater offers to update most of these when the project opens. Accept it, then fix what remains by hand using the mapping on this page; optimizeMesh always needs a decision between the two new properties.

Sources

Related Unity 6 changes

Every Unity 6.x change, by version