PIs</strong> for headers, trailers and metadata.</li><li><strong>Call out APIs</strong> for gRPC and HTTP calls.</li><li><strong>Stats and Logging APIs</strong> for metrics and monitoring.</li></ul><figure style=width:80%><div class=wrapper-with-intrinsic-ratio style=padding-bottom:75%><a data-skipendnotes=true href=/v1.11/docs/concepts/wasm/extending.svg title="Extending Istio/Envoy"><img class=element-to-stretch src=/v1.11/docs/concepts/wasm/extending.svg alt="Extending Istio/Envoy"></a></div><figcaption>