diff --git a/src/effect/schema/class/Mutable.ts b/src/effect/schema/class/Mutable.ts
index e69de29..d041490 100644
--- a/src/effect/schema/class/Mutable.ts
+++ b/src/effect/schema/class/Mutable.ts
@@ -0,0 +1,62 @@
+import { Schema as S } from "@effect/schema"
+import type { Annotations, Class, Struct } from "@effect/schema/Schema"
+import type { Mutable } from "effect/Types"
+import type { Constructor } from "type-fest"
+import type { StaticType } from "../../.."
+import type { HasFields, MissingSelfGeneric } from "./util"
+
+
+export type TMutableClass<
+    Self,
+    Fields extends Struct.Fields,
+    I, R, C,
+    Inherited,
+    Proto,
+> = (
+    Constructor<
+        Omit<
+            InstanceType<Class<Self, Fields, I, R, C, Inherited, Proto>>,
+            keyof Fields
+        > &
+        Mutable<Struct.Type<Fields>>,
+
+        ConstructorParameters<Class<Self, Fields, I, R, C, Inherited, Proto>>
+    > &
+
+    Omit<
+        StaticType<Class<Self, Fields, I, R, C, Inherited, Proto>>,
+        "extend"
+    > & {
+        extend<Extended = never>(identifier: string): <newFields extends Struct.Fields>(
+            fields:        newFields | HasFields<newFields>,
+            annotations?:  Annotations.Schema<Extended>,
+        ) => [Extended] extends [never]
+            ? MissingSelfGeneric<"Base.extend">
+            : TMutableClass<
+                Extended,
+                Fields & newFields,
+                I & Struct.Encoded<newFields>,
+                R | Struct.Context<newFields>,
+                C & Struct.Constructor<newFields>,
+                Self,
+                Proto
+            >
+    }
+)
+
+
+export function Mutable<
+    This extends Class<Self, Fields, I, R, C, Inherited, Proto>,
+
+    Self,
+    Fields extends Struct.Fields,
+    I, R, C,
+    Inherited,
+    Proto,
+>(
+    class_:
+        | This
+        | Class<Self, Fields, I, R, C, Inherited, Proto>
+) {
+
+}