https://www.esrb.org/ratings-guide/
From the campaign gameplay demo, I saw:
No substance references
Animated Blood - Discolored and/or unrealistic depictions of blood.
Violence - Scenes involving aggressive conflict. May contain bloodless dismemberment (but i didn’t see dismemberment).
No notable humor
No notable language
No nudity
No gambling
No sexuality
It’s likely that, when humans get shot, there will be Blood - Depictions of blood.
I would argue that, due to all the weapons in Halo Infinite having colored tracer lines, the game has Fantasy Violence - Violent actions of a fantasy nature, involving human or non-human characters in situations easily distinguishable from real life.
Note though, that all Halo games have Violence in their ESRB label. Additionally, Destiny 1 & 2 both have Violence in their ESRB label, so i guess it’s pretty difficult to get labeled Fantasy Violence. It doesn’t really matter though, for a Teen rating.
It’s possible that, if there are non-paid loot boxes, the game could get Simulated Gambling - Player can gamble without betting or wagering real cash or currency.
I think Halo Infinite will be rated Teen - Content is generally suitable for ages 13 and up. May contain violence, suggestive themes, crude humor, minimal blood, simulated gambling, and/or infrequent use of strong language.
Adding splattering blood like CE might be enough to take it out of the “minimal blood” category. Additionally, the flood may be enough to take it to Blood and Gore - Depictions of blood or the mutilation of body parts.
Note that Halo 1-3 had blood and gore on their ESRB label, while Halo OSDT, Reach, and 4 only had Blood (but still rated M). They toned down the blood for Halo 5 and got a T rating (but still have Blood on the label, must be “minimal” enough). Thus, removing the flood gets rid of the gore, but they also have to tone down the blood to get a T rating, it seems.
So, we may be seeing Prometheans instead of the Flood as Halo Infinite’s “big twist”. I hope they’ll be distinguished from other Forerunner stuff, so we can still have the classic standard of four factions.
With multiplayer and microtransactions, Halo Infinite will also get:
In-Game Purchases - Contains in-game offers to purchase digital goods or premiums with real world currency, including but not limited to bonus levels, skins, music, virtual coins and other forms of in-game currency, subscriptions, season passes and upgrades (e.g., to disable ads).
Users Interact - Indicates possible exposure to unfiltered/uncensored user-generated content, including user-to-user communications and media sharing via social media and networks.
These are additional tags that don’t seem to affect the rating, but are added below the main label to let people know if those noteworthy features are in the game.