How to reproduce:
1. Open the attached “IN-133098” project
2. Open the “Scene” scene
3. Enter Play mode
4. Observe the Console window

Actual result: “actual: Interpolate(5, 46, 1) = 0” is logged
Expected result: “actual: Interpolate(5, 46, 1) = 46” is logged

Reproducible with: 2.6.1 (6000.0.23f1 (1c4764c07fb4)), 2.8.2 (6000.0.67f1, 6000.3.7f1, 6000.4.0b8, 6000.5.0a6)

Reproducible on: macOS 26.2 (M1 Max)
Not reproducible on: No other environments tested

Note: Source for the expected result https://docs.unity3d.com/Packages/com.unity.splines@2.8/api/UnityEngine.Splines.Interpolators.SmoothStepFloat.html