A metering layer, a rating layer and an invoicing layer — plus a CRM contract model that can express commitment-plus-overage. Most consumption businesses meter through their warehouse and Stripe; only about a fifth run a purpose-built metering engine such as Metronome, Orb, Lago or Ordway.
Tier configuration itself is largely solved — commitment-plus-overage, stair-step, volume, unlock-the-lower-tier are all standard. The hard part is downstream: recognising revenue against consumption, forecasting a number sellers don't control, and giving CS a view of burn-down before the customer sees the invoice.
Every claim above comes from work LeanScale published. These are the sources.