diff --git a/what4-transition-system/what4-transition-system.cabal b/what4-transition-system/what4-transition-system.cabal
index 265b061c..952f5e56 100644
--- a/what4-transition-system/what4-transition-system.cabal
+++ b/what4-transition-system/what4-transition-system.cabal
@@ -20,7 +20,7 @@ common dependencies
     , lens
     , parameterized-utils  >=2.0  && <2.2
     , text
-    , what4                ^>=1.5
+    , what4                ^>=1.6
 
 library
   import:           dependencies
diff --git a/what4/CHANGES.md b/what4/CHANGES.md
index 2df6bf71..14bb5742 100644
--- a/what4/CHANGES.md
+++ b/what4/CHANGES.md
@@ -1,4 +1,4 @@
-# next (TBA)
+# 1.6 (May 2024)
 
 * Allow building with GHC 9.8.
 
diff --git a/what4/what4.cabal b/what4/what4.cabal
index 4ea6f51e..f8be582b 100644
--- a/what4/what4.cabal
+++ b/what4/what4.cabal
@@ -1,6 +1,6 @@
 Cabal-version: 2.4
 Name:          what4
-Version:       1.5.1.0.99
+Version:       1.6
 Author:        Galois Inc.
 Maintainer:    rscott@galois.com, kquick@galois.com
 Copyright:     (c) Galois, Inc 2014-2023