Yes, with no separate plan and no agency setup step. Sign up like anyone else and add each client as a store, from your Google connection or your manager account. Optimize works on every store the same way.
Every account can put its own brand on reports, and you pay the same 5% of each client's Google Ads spend, all on one card.
The full detail: For agencies.
See it on your own accounts
Free plan, no card: see everything Optimize would change before you pay.