diff --git a/schemas/core.yaml b/schemas/core.yaml
index 2f8be44..4c629aa 100644
--- a/schemas/core.yaml
+++ b/schemas/core.yaml
@@ -98,6 +98,7 @@ classes:
     extends: Object
     isCoreType: true
     mixins:
+      - ActivityMixin
     properties:
       actor:
         type: WrapAS2[Object] | str | None
diff --git a/src/apmodel/mixins/activity.py b/src/apmodel/mixins/activity.py
new file mode 100644
index 0000000..9278b34
--- /dev/null
+++ b/src/apmodel/mixins/activity.py
@@ -0,0 +1,18 @@
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from apmodel.activity import Accept, Reject
+    from apmodel.core import Activity
+    from apmodel.objects import Actor
+
+
+class ActivityMixin:
+    def accept(self: "Activity", id: str, actor: "Actor") -> "Accept":
+        from apmodel.activity.accept import Accept
+
+        return Accept(id=id, actor=actor, object=self)
+
+    def reject(self: "Activity", id: str, actor: "Actor") -> "Reject":
+        from apmodel.activity.reject import Reject
+
+        return Reject(id=id, actor=actor, object=self)
diff --git a/vendor/activitystreams b/vendor/activitystreams
index a7071ff..3515da4 160000
--- a/vendor/activitystreams
+++ b/vendor/activitystreams
@@ -1 +1 @@
-Subproject commit a7071ff7473611efea933bf73c277ea73bcc79cb
+Subproject commit 3515da42e6b0f283cc53dec3cb35f1e9422b2022