Group 14 endohedral clusters containing a metal center inside usually possess a single cage topological structure, but here an unexpected single‐metal‐filled double‐cage cluster, [Pt@Sn17]4− (1 a) is reported. It can be seen as a combination of the more extended Pt‐filled [Pt@Sn9] cage and hollow [Sn9] cage sharing a central Sn atom, which is offset from the central position. This double‐cage species represents the largest group 14 intermetalloid cluster encapsulating a single transition metal atom. DFT calculations show that the capsule‐like architecture of [Sn17]4−, similar to that found in [Pt2@Sn17]4−, is unstable if filled with a single Pt atom and collapses to the title cluster 1 a upon geometry optimization. Deviation of the central Sn atom occurs due to the vibronic coupling as a consequence of pseudo‐Jahn‐Teller distortion leading to the bent Cs‐symmetrical structure, in contrast to the more symmetrical D2d cage previously reported in [Ni2@Sn17]4−.