Rockstar has not mentioned it once. Not in a trailer, not on a store page, not in the 26-minute showcase - which is notable, because that video had plenty of room to show it.
Why so many people assume it is in
GTA V shipped in 2013 without first-person. The mode arrived with the 2014 console re-release and turned out to be a substantial piece of work: separate animations for entering vehicles, reworked weapon handling, a whole second camera rig. Red Dead Redemption 2 then shipped with first-person in the box in 2018. Two consecutive Rockstar open worlds supporting it makes a third feel like a safe bet.
Reasons for caution
- Nothing in official footage has been shown from a first-person camera
- The character animation work on display is heavily third-person framed
- Rockstar has historically announced this mode as a feature, not left it unmentioned
The last point cuts both ways. Rockstar also holds features back deliberately, and a marketing campaign that has so far shown two characters and a state has not shown much of anything about camera options, control schemes or accessibility settings either.
What would count as confirmation
A store page feature list, a settings menu shown in footage, or an accessibility page. None of those exist yet. The PlayStation and Xbox store listings describe the game in broad terms and do not enumerate camera modes.
The honest position
Likely, given the pattern. Unstated, given the evidence. If a first-person mode is a deciding factor for you, wait for reviews rather than pre-ordering on the strength of a trend.
Anything Rockstar says on the subject goes straight into the news feed, and the videos worth re-watching frame by frame are on the trailers page.