we consider ricci flows admitting closed and smooth tangent flows in the sense of bamler 20. the tangent flow in question can be either a tangent flow at infinity for an ancient ricci flow, or a tangent flow at a singular point for a ricci flow developing a finite-time singularity. in these cases, we show that the tangent flow is unique and the singularity is of type i. this talk is based on a joint work with zilu ma and yongjia zhang.