UPGRADING.md

@@ -1,3 +1,13 @@
+# Release 2.0.3
+
+2.0.3 is a maintenance release with no public API or ABI changes. Compared
+with 2.0.2, the project now has:
+
+* AddressSanitizer and UndefinedBehaviorSanitizer coverage in CI, so the
+  regular test suite is exercised under both sanitizers.
+* A repeatable `--cmake-arg` option for `scripts/mutation_test.py`, allowing
+  mutation runs to cover alternate CMake configurations such as ThreadSanitizer.
+
 # Bug fix: the AKERR_USE_STDLIB=OFF build, and a pool-exhaustion exit code (2.0.2)
 
 `-DAKERR_USE_STDLIB=OFF` did not compile at all ([issue #12](https://source.starfort.tech/andrew/libakerror/issues/12)):