High Concurrency clusters are designed for multi-user environments where many users run queries at the same time. According to the Databricks community reference, these clusters support SQL, Python, and R, but do not support Scala.

This limitation exists because High Concurrency clusters run each user’s code in separate, isolated processes to ensure better security and stable performance. Scala runs on the JVM and cannot be isolated this way, so it is not supported.

Therefore, any language combination that includes Scala is not supported on High Concurrency clusters. This is why options containing Scala (such as SQL and Scala, Python and Scala, or Scala and R) are invalid.

Reference: https://community.databricks.com/t5/data-engineering/when-to-use-high-concurrency-clusters-what-are-the-benefits/m-p/26520#M18553