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The size frequency distribution of exoplanet radii between 1 and4$R_{\oplus}$ is bimodal with peaks at $\sim$1.4 $R_{\oplus}$ and $\sim$2.4$R_{\oplus}$, and a valley at $\sim$1.8$R_{\oplus}$. This radius valleyseparates two classes of planets -- usually referred to as "super-Earths" and"mini-Neptunes" -- and its origin remains debated. One model proposes thatsuper-Earths are the outcome of photo-evaporation or core-powered mass-lossstripping the primordial atmospheres of the mini-Neptunes. A contrasting modelinterprets the radius valley as a dichotomy in the bulk compositions, wheresuper-Earths are rocky planets and mini-Neptunes are water-ice rich worlds. Inthis work, we test whether the migration model is consistent with the radiusvalley and how it distinguishes these views. In the migration model, planetsmigrate towards the disk inner edge forming a chain of planets locked inresonant configurations. After the gas disk dispersal, orbital instabilities"break the chains" and promote late collisions. This model broadly matches theperiod-ratio and planet-multiplicity distributions of Kepler planets, andaccounts for resonant chains such as TRAPPIST-1, Kepler-223, and TOI-178. Here,by combining the outcome of planet formation simulations with compositionalmass-radius relationships, and assuming complete loss of primordial H-richatmospheres in late giant-impacts, we show that the migration model accountsfor the exoplanet radius valley and the intra-system uniformity("peas-in-a-pod") of Kepler planets. Our results suggest that planets withsizes of $\sim$1.4 $R_{\oplus}$ are mostly rocky, whereas those with sizes of$\sim$2.4 $R_{\oplus}$ are mostly water-ice rich worlds. Our results do notsupport an exclusively rocky composition for the cores of mini-Neptunes.

The Exoplanet Radius Valley from Gas-driven Planet Migration and Breaking of Resonant Chains