Once and for All, Without Making My Head Spin: Can Someone Explain the Difference Between USMLE Step 2 CK and Step 3 https://uadviser.us/once-and-for-all-without-making-my-head-spin-can-someone-explain-the-difference-between-usmle-step-2-ck-and-step-3/ You take their word for it because they clearly know something you don’t. After All, it must be a completely different beast: It spans two days, contains the mysterious CCS portion, and is the final step before full licensure. It feels like facing the final boss in a video game.