Two Sigma & Citadel Onsites : Coding/System Design level ?

My Two Sigma and Citadel onsites are coming up. Can anybody who has attended these recently provide some clues on the level of coding / system design ? Is coding LC medium or hard ? Is doing LC company-tagged questions enough ? Does TS ask standard system design questions, or is it mostly around Object oriented design ? How about Citadel ? This is for a Senior/Staff engineer level role. 12 YOE TC: 350K