diff --git a/README.md b/README.md
index 1a4a7c39c..34651c19a 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,13 @@ The autogenerated OSAL user's guide can be viewed at <https://github.com/nasa/cF
 
 ## Version History
 
+### Development Build: v6.0.0-rc4+dev66
+
+- Fix UtAssert_StringBufCompare SEGV when -1 for size passed in (on CentOS 7)
+- Enable format check workflow on push to all branches
+- Update Copyright Headers
+- Standardize version.h 
+- See <https://github.com/nasa/osal/pull/1239> and <https://github.com/nasa/cFS/445>
 ### Development Build: v6.0.0-rc4+dev54
 
 - Revert development version identifier to 99 for revision number
diff --git a/src/os/inc/osapi-version.h b/src/os/inc/osapi-version.h
index da055e244..3e6a9355d 100644
--- a/src/os/inc/osapi-version.h
+++ b/src/os/inc/osapi-version.h
@@ -34,7 +34,7 @@
 /*
  * Development Build Macro Definitions
  */
-#define OS_BUILD_NUMBER   54
+#define OS_BUILD_NUMBER   66
 #define OS_BUILD_BASELINE "v6.0.0-rc4"
 
 /*