Detailed description of how Object.Destroy() and Object.DestroyImmediate() behaves in Unity 6.3 with destroyCancellationToken. There is a script you can use in your environment to test the behavior.

DestroyCancellationTokeTest.cs

using System.Threading;
using UnityEngine;


public class DestroyCancellationTokeTest : MonoBehaviour
{
    private CancellationToken _token;

    private void Awake()
    {
        Log($"Awake(), default state: {_token.CanBeCanceled} {_token.IsCancellationRequested}");
    }

    private void OnEnable()
    {
        _token = destroyCancellationToken;
        Log($"OnEnable(), created state: {_token.CanBeCanceled} {_token.IsCancellationRequested}");
        Log($"OnEnable(), are equal: {_token == destroyCancellationToken}");

        _token.Register(() => { this.Log($"Registered synchron callback: {this._token.CanBeCanceled} {this._token.IsCancellationRequested}"); }, true);
        _token.Register(() => { this.Log($"Registered not synchron callback: {this._token.CanBeCanceled} {this._token.IsCancellationRequested}"); }, false);
        _token.Register(() => { this.Log($"Registered not synchron2 callback: {this._token.CanBeCanceled} {this._token.IsCancellationRequested}"); }, false);
        _token.Register(() => { this.Log($"Registered synchron2 callback: {this._token.CanBeCanceled} {this._token.IsCancellationRequested}"); }, true);
    }

    private void Start()
    {
        Log($"Start(), before destroy call: {_token.CanBeCanceled} {_token.IsCancellationRequested}");
        
        // # Behavior of Object.Destroy() in Unity 6.3:
        // # 1. this.OnDisable() called immediately, before next line.
        // # 2. Next line after Destroy() is executed with `this != null`.
        // # All next steps are delayed. 
        // # 3. Internally `_token.IsCancellationRequested` is set to `true`.
        // # 4. Calls token's registered callbacks in **REVERSE** order.
        // # 5. Calls this.OnDestroy().
        // # NOTE: Unity's null check `this == null` **NEVER** returns true in this chain.
        // # NOTE: After Destroy() is called no other callbacks (Update, LateUpdate) will be invoked despite delayed execution of steps 3,4,5.
        Destroy(this); 
        
        // # Behavior of Object.DestroyImmediate() in Unity 6.3:
        // # 1. this.OnDisable() called immediately, before next line. `this != null` and `isCancelled == false`.
        // # 2. Internally `_token.IsCancellationRequested` is set to `true`.
        // # 3. Calls registered callbacks in **REVERSE** order. `this != null` and `isCancelled == true`.
        // # 4. Calls this.OnDestroy() immediately, before next line. `this != null` and `isCancelled == true`.
        // # 5. Next line after DestroyImmediate() is executed, finally `this == null`.
        // DestroyImmediate(this); 
        Log($"Start(), after destroy call: {_token.CanBeCanceled} {_token.IsCancellationRequested}");
    }

    private void Update()
    {
        Log($"Update() {_token.CanBeCanceled} {_token.IsCancellationRequested}");
    }

    private void LateUpdate()
    {
        Log($"LateUpdate() {_token.CanBeCanceled} {_token.IsCancellationRequested}");
    }

    private void OnDisable()
    {
        Log($"OnDisable() {_token.CanBeCanceled} {_token.IsCancellationRequested}");
    }

    private void OnDestroy()
    {
        Log($"OnDestroy() {_token.CanBeCanceled} {_token.IsCancellationRequested}");
    }

    private void Log(string message)
    {
        Debug.Log($"[DestroyCancellationTokeTest] {message}, {(this == null ? "THIS IS NULL" : "")}");
    }
}

Docs.md

Behavior of Object.Destroy() in Unity 6.3:

1. this.OnDisable() called immediately, before next line.
2. Next line after Destroy() is executed with this != null. All next steps are delayed.
3. Internally _token.IsCancellationRequested is set to true.
4. Calls token's registered callbacks in REVERSE order.
5. Calls this.OnDestroy(). NOTE: Unity's null check this == null NEVER returns true in this chain. NOTE: After Destroy() is called no other callbacks (Update, LateUpdate) will be invoked despite delayed execution of steps 3,4,5.

Behavior of Object.DestroyImmediate() in Unity 6.3:

1. this.OnDisable() called immediately, before next line. this != null and isCancelled == false.
2. Internally _token.IsCancellationRequested is set to true.
3. Calls registered callbacks in REVERSE order. this != null and isCancelled == true.
4. Calls this.OnDestroy() immediately, before next line. this != null and isCancelled == true.
5. Next line after DestroyImmediate() is executed, finally this == null.

Docs_ChatGPT.md

Unity Object Destruction Semantics (Unity 6.3) summary by ChatGPT

Scope: This document describes observable behavior of Object.Destroy and Object.DestroyImmediate in Unity 6.3.
Any implementation details are explicitly marked and must not be relied upon as API guarantees.

Important: All null checks mentioned here refer to Unity’s overloaded
UnityEngine.Object == null, not CLR reference null.

---

Object.Destroy()

Summary

Disable immediately, destroy later (end of frame).

Immediate effects (during the call)

• OnDisable() is invoked immediately, before Destroy() returns.
• After the call returns, the object is still considered alive:
  • this != null evaluates to true.
  • Script execution continues normally.

Deferred effects (destruction finalization)

• The object is marked for destruction and finalized later in the same frame.
• During finalization:
  • OnDestroy() is invoked.
  • After this point, this == null evaluates to true.

Execution guarantees

• After Destroy() is called:
  • No further lifecycle callbacks (Update, LateUpdate, etc.) will be invoked.
  • The object should be treated as logically dead, even though destruction is deferred.

Implementation details (non-contractual)

• Internally, Unity cancels the object’s lifetime token and invokes its registered callbacks.
• Callback invocation order has been observed to be reverse registration order.
• These details are not part of Unity’s public API and may change.

---

Object.DestroyImmediate()

Summary

Destroy immediately and synchronously.

Immediate effects (during the call)

• OnDisable() is invoked immediately.
• The object is destroyed synchronously.
• OnDestroy() is invoked before DestroyImmediate() returns.

After the call returns

• The object is fully destroyed.
• this == null evaluates to true.
• Any further access to the object must be treated as invalid.

Implementation details (non-contractual)

• Lifetime cancellation and registered callbacks are triggered during the call.
• Observed behavior places these callbacks before OnDestroy().
• This ordering is not guaranteed by the API.

---

Practical Guidelines

• Prefer Destroy() in gameplay code.
• Use DestroyImmediate() only when explicitly required (e.g. editor tooling).
• Never rely on:
  • Internal cancellation tokens
  • Callback ordering
  • Exact timing beyond what is documented above
• After calling Destroy():
  • Do not expect further updates
  • Do not schedule work assuming the object will survive the frame

---

Rule of Thumb

• Destroy() → disable now, destroy later
• DestroyImmediate() → destroy now