Unity 7 alpha vs Unity 6. What changed for game developers?

The Editor runs on CoreCLR now

Takeaway: The runtime changed, the language did not. Unity 7 alpha is Unity 6 C# running on a new engine.

What is in the alpha, and what is not

Takeaway: The alpha is the new foundation. Most things people are excited about come later, on top of it.

Is Unity 7 faster?

Takeaway: Do not upgrade for speed. Expect about the same frame times as in 6.7.

Deprecated and removed in Unity 7

Takeaway: Built-in Render Pipeline, CPU lightmaps, and Intel Macs are the three things that stop you on day one.

Code that changes

Static fields are not reset anymore

using System.Collections.Generic;
using Unity.Scripting.LifecycleManagement;

public static class EnemyCache
{
    public static readonly List<Enemy> Alive = new List<Enemy>();

    // Runs after Unity reloaded your code. Clear what domain reload used to clear.
    [AfterCodeReloadSerialization]
    static void Cleanup()
    {
        Alive.Clear();
    }
}

Asset importers have to set the main object

public class MyModelPostprocessor : AssetPostprocessor
{
    void OnPostprocessModel(GameObject root)
    {
        var extra = ScriptableObject.CreateInstance<MyData>();
        context.AddObjectToAsset("data", extra);

        // New in Unity 7. Without this line the model stays the main object.
        context.SetMainObject(extra);
    }
}

Takeaway: Search your project for static collections, AddObjectToAsset, and Assembly.Location. Those three searches find most of the work.

Should you try the alpha?