At that time there was still examination whether a thin, sharply swept wing or a pure delta layout would be of more advantage and additionally it was desired to adopt a tailplane with a thin aerofoil. This led within the OKB to the decision to construct simultaneously test-beds for both wing layouts.
First prototype to be finished was swept-wing one. Originally intended for the AM-5A engine, it was designated Ye-1 (E-1). But during the design stage more powerful afterburning AM-9B became available. Airframe was modified to accommodate the new engine, and aircraft materialized as Ye-2.