Final answer:
Oracle Cloud Infrastructure Functions (OCI Functions) is the OCI service that allows the running of code without provisioning virtual machines, exemplifying a server-less architecture where you only pay for the compute time used.
Step-by-step explanation:
The OCI service that enables you to run code without provisioning any underlying infrastructure, such as virtual machines, is called Oracle Cloud Infrastructure Functions (OCI Functions). OCI Functions is a serverless platform that operates on a pay-as-you-go model, allowing developers to write, deploy, and run code without managing servers. This service automatically scales the compute resources to match the number of requests your function code receives. The server-less architecture of OCI Functions means you only pay for the compute time you consume, making it a cost-effective solution for running event-driven applications or services.