How tier relates to AI brain

Every employee has a tier, and which AI brain tier uses is different. Interns use a light, fast brain, while team members, seniors, and team leads use progressively smarter ones. Brain credit usage also scales with tier (team-member tier uses 4x an intern's, team-lead tier uses 10x).

Sending easy work to interns and important judgment calls to higher tiers is also better for cost. You can see and change which tier uses which brain in Settings > AI brain settings. The free plan can only use intern tier; upgrading your plan unlocks higher tiers.