A method for speculative object shapes comprises obtaining values for objects of a first and second shape, determining, by a processor and during runtime, a first speculative type for the first value and a second speculative type for the second value, generating, based on the first speculative type and the second speculative type, a shape tree comprising a first subtree for the first shape and a second subtree for the second shape, marking, by the processor, the first subtree as obsolete based on a determination that the first speculative type is incorrect and that the second shape is a super shape of the first shape, and transforming, in response to marking, the first object from the first shape to the second shape by: merging the first subtree into the second subtree.