Transparent single crystals of Cs8[Si6O16] have been obtained by a high‐temperature reaction at 900 °C in an arc‐welded niobium crucible. The structure of Cs8[Si6O16] was solved and refined from single crystal X‐ray diffraction data: new structure type, P$\bar{1}$, Z = 2, a = 9.3544(3) Å, b = 11.1152(4) Å, c = 13.5035(5) Å, α = 101.311(3)°, β = 100.958(3)°, γ = 114.121(3)°, R1 = 0.032. The structure of Cs8[Si6O16] contains isolated dimeric cyclotrisilicate anions [Si6O16]8– that are separated by cesium atoms.The anion consists of six vertex‐sharing [SiO4] tetrahedra which form three interconnected rings: two rings consisting of three tetrahedra share edges with the opposite sides of a square of four [SiO4] thetrahedra. With respect to the plane of the four‐membered rings the triangles strike a trans‐type arrangement. [Si6O16]8– is the first example of the third possible structural arrangement in the class of unbranched dimeric cyclotrisilicate anions.