Start here. This is the direct spoken answer to practice first.
Overview
Capability is a property demonstrated on tasks; reliability is an end-to-end property engineered around users, dependencies, and consequences.
Model capability describes the kinds of tasks a model can perform and how well it performs them under an evaluation. Application reliability describes whether the complete feature delivers acceptable behavior consistently in production. Reliability includes input handling, authorization, retrieval, model availability, output validation, latency, fallbacks, monitoring, and recovery. A capable model can sit inside an unreliable application, and a well-designed application can use a less capable model reliably for a bounded task.