diff --git a/packages/opencode/src/session/index.ts b/packages/opencode/src/session/index.ts
index 55532a7946..2375d8333d 100644
--- a/packages/opencode/src/session/index.ts
+++ b/packages/opencode/src/session/index.ts
@@ -851,14 +851,4 @@ export namespace Session {
     return runPromise((svc) => svc.updatePart(part))
   }
 
-  export const updatePartDelta = fn(
-    z.object({
-      sessionID: SessionID.zod,
-      messageID: MessageID.zod,
-      partID: PartID.zod,
-      field: z.string(),
-      delta: z.string(),
-    }),
-    (input) => runPromise((svc) => svc.updatePartDelta(input)),
-  )
 }