Tensionless string spectra on ${AdS}_3$

The spectrum of superstrings on ${AdS}_3\times S^3\times M_4$ with pure NS-NS flux is analysed for the background where the radius of the AdS space takes the minimal value $(k=1)$. Both for $M_4=S^3\times S^1$ and $M_4=T^4$ we show that there is a special set of physical states, coming from the bottom of the spectrally flowed continuous representations, which agree in precise detail with the single particle spectrum of a free symmetric product orbifold. For the case of ${AdS}_3\times S^3\times T^4$ this relies on making sense of the world-sheet theory at $k=1$, for which we make a concrete proposal. We also comment on the implications of this striking result.