From the blog:

A new Big Team Battle mode has arrived in Halo Infinite. Introducing BTB: Sentry Defense!

Adjutant Resolution, one of Zeta Halo’s submonitors who you met and fought in Halo Infinite’s campaign, has decided to jump into some multiplayer action. Two of them—simply known as “sentries” in this context—are on each team; your objective is to protect your sentries and destroy the enemy’s.

Each team has 2,000 points. As damage is dealt to your sentries, the available score drops, and if you reach 0 it’s game over. Each map will have at least one Repair Field that spawns in a neutral location—in addition to providing health regeneration for your fellow Spartans and vehicles, it’ll also repair your sentries.

BTB: Sentry Defense will be playable on:

• Fragmentation
• Highpower
• Deadlock
• Oasis
• Scarr
• Command