The bootloader is still locked, but kit Kat has root access! Install towelroot to root your at&t note 3 running kit Kat. Then search the development section for what rom you desire and follow it's instructions. Generally you'll install superuser, safestrap, and busy box. Then please don't forget to BACKUP before installing custom rom to stock slot.
Start rooting your device here.
Click the Greek a looking symbol and download the app.