> Would love feedback on the API design

I'd suggest to drop the DSL, at the end of the day, a good old class with a constructor stored in a constant is much more more transparent:

    class PaymentService
      STRIPE_CIRCUIT = BreakerMachines::Circuit.new(
        threshold: { failures: 3, within: 1.minute },
        reset_after: 30.seconds,
        fallback: ->{ { error: "Payment queued for later" } }
      )

      def charge(amount)
        STRIPE_CIRCUIT.wrap do
          Stripe::Charge.create(amount: amount)
        end
      end
    end

Just my 2 cents though.