A read once ABP is an arithmetic branching program with each variable occurring in at most one layer. We give the first polynomial time whitebox identity test for a polynomial computed by a sum of constantly many ROABPs. We also give a corresponding blackbox algorithm with quasi-polynomial time complexity, i.e. n O ( log n ) . The motivating special case of this model is sum of constantly many set-multilinear depth- 3 circuits. The prior results for that model were only slightly better than brute-force (i.e. exponential-time).