diff --git a/specification/trace/sdk.md b/specification/trace/sdk.md
index 6a315d11b6f..063770e873f 100644
--- a/specification/trace/sdk.md
+++ b/specification/trace/sdk.md
@@ -204,6 +204,12 @@ Note: Implementation-wise, this could mean that `Tracer` instances have a
 reference to their `TracerProvider` and access configuration only via this
 reference.
 
+The SDK MUST provide a mechanism for customizing the way IDs are generated for
+both the `TraceId` and the `SpanId`.
+
+The SDK should by default randomly generate the bytes for both the `TraceId` and
+the `SpanId`.
+
 ### Shutdown
 
 This method provides a way for provider to do any cleanup required.