diff --git a/docs/Architecture/LargeScale.md b/docs/Architecture/LargeScale.md
index d6419f225..80063bebd 100644
--- a/docs/Architecture/LargeScale.md
+++ b/docs/Architecture/LargeScale.md
@@ -33,7 +33,16 @@ layout: doc_page
 	* The C++ Core is extended using the python binding library [pybind11](https://github.com/pybind/pybind11) enabling high performance operation from Python.
 
 ### Cross Language Binary Compatibility
-* Sketches serialized from C++ or Python can be interpreted by compatible Java sketches and visa versa. 
+* Sketches serialized from C++ or Python can be interpreted by compatible Java sketches and visa versa.
+
+* A current library version can read serialized images of sketches from older _or_ newer library
+versions within a language. In the serialized form, sketches contain a version number which allows
+the library to deserialize sketches produced by older versions of the library.
+
+* The current version of a serialized sketch is compatible across languages
+with the caveat that a new sketch may be introduced in one language before being ported to others.
+Sketches requiring user-written custom serialize/deserialize code rely on users to port that custom
+code themselves for cross-language compatibility.
 
 ### Speed
 * These single-pass, "one-touch" algorithms are <i>fast ([see example](https://datasketches.apache.org/docs/Theta/ThetaUpdateSpeed.html))</i> to enable real-time processing capability.