public double getVectorSimilarityThreshold() {
        if (vectorDbThresholdCase_ == 4) {
          return (java.lang.Double) vectorDbThreshold_;
        }
        return 0D;
      }
<pre>
Optional. Only returns contexts with vector similarity larger than the
threshold.
</pre>

<code>double vector_similarity_threshold = 4 [(.google.api.field_behavior) = OPTIONAL];
</code>

@return The vectorSimilarityThreshold.
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/RagRetrievalConfig.java