Comment by shusson

Answering based on my own experience transferring to an E3 from E3D. You can apply for E3 from within US, but you will not be able to travel outside the US because you won’t get a visa stamp. You will also likely want to pay for premium processing if going through USCIS. Alternatively, you can apply at a consulate outside the US, which gives you a stamp. https://americajosh.com is a good resource for E3s.