Very little is known about Thief 4 as Eidos and Square Enix have kept quiet. At least fans know to expect third-person views in the game, at least during archery.
Theof the playtest at Eidos Montreal was spotted by (translated) where they mention a mixture of the third-person view is used when Garrett is travelling, climbing and using archery. This image at least proves it true for archery.
Are you looking forward to Thief 4, videogamer?