The New Relic Java agent is compatible with Scala, and supports New Relic API calls, annotations, and custom instrumentation. All information below is supplemental to New Relic's Java agent installation directions.
For Heroku, see Java agent with Scala on Heroku.
Instrument Scala to use the New Relic API class or annotations.
Add the following information to your Scala configuration file:
Import the NewRelic class and use it in your application:
import com.newrelic.api.agent.NewRelic ... NewRelic.setTransactionName(null, "/myTransaction");
For more about the Java agent API and its functionality, see the Java agent API introduction.
If you use Kamon, take a look at the New Relic Kamon reporter.