diff --git a/sdk/lib/opentelemetry/sdk/trace/span_processor.rb b/sdk/lib/opentelemetry/sdk/trace/span_processor.rb
index c5c7c7e17..089c9b3b2 100644
--- a/sdk/lib/opentelemetry/sdk/trace/span_processor.rb
+++ b/sdk/lib/opentelemetry/sdk/trace/span_processor.rb
@@ -23,6 +23,8 @@ class SpanProcessor
         #  started span.
         def on_start(span, parent_context); end
 
+        # The on_ending is an experimental feature and may have breaking changes.
+        #
         # Called when a {Span} is ending, after the end timestamp has been set
         # but before span becomes immutable. This allows for updating the span
         # by setting attributes or adding links and events.