[esafak]

That looks like a built-in feature. I'm asking about extensibility. How do we use custom metrics transformations (libraries), for example?

[nikolay_sivko]

Currently, you can define custom SLIs (Service Level Indicators, such as service latency or error rate) for each service using PromQL queries. In the future, you'll be able to define custom metrics for each application, including explanations of their meaning, so they can be leveraged in Root Cause Analysis