Does SerializeField work when extending the Input System?

I am extending the new Input System with a custom Processor and Interaction.

Using a public field shows up in the Editor as expected:

public float tweakableValue = 2.5f;

However, I prefer to use SerializeField to indicate that this is set in the Editor and prevent access from other classes:

private float tweakableValue = 2.5f;

While this works perfectly well for any MonoBehaviour, it does not show up in the Input Action Editor.

Am I missing something or is this simply not supported by the new Input System?
If so, should I report a bug?

Edit: Here is an example where I extend the InputProcessor:

using UnityEngine;
using UnityEngine.InputSystem;
using UnityEditor;

namespace dyco {

/// <summary>
/// Input processor to rotate a two dimensional input by the configured degrees
/// </summary>
public class RotateProcessor : InputProcessor<Vector2> {
    [Tooltip("The angle in degrees to rotate the vector by")]
    public float RotateDegrees = 45f;

    static RotateProcessor() {

    private static void Initialize() {

    /// <summary>Rotates the given vector <paramref name="value"/> by the configured <see cref="RotateDegrees"/></summary>
    public override Vector2 Process(Vector2 value, InputControl control) {
        return value.Rotate(RotateDegrees);

How do you extend the input system? Most of Unity’s build-in classes have a dedicated custom editor created for that class. So if you derive your own class from one of them, you often have to create / extend the editor as well.