diff --git a/altair/__init__.py b/altair/__init__.py
index 5bb1b9cff..8184d1722 100644
--- a/altair/__init__.py
+++ b/altair/__init__.py
@@ -1,5 +1,5 @@
 # ruff: noqa
-__version__ = "5.1.2"
+__version__ = "5.2.0dev"
 
 from typing import Any
 
diff --git a/doc/conf.py b/doc/conf.py
index 008fbd36c..b78551ca1 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -76,7 +76,7 @@
 # built documents.
 #
 # The short X.Y version.
-version = "5.1.2"
+version = "5.2.0dev"
 # The full version, including alpha/beta/rc tags.
 release = f"{version}"
 
diff --git a/doc/releases/changes.rst b/doc/releases/changes.rst
index 56c48a18a..a6b52efd1 100644
--- a/doc/releases/changes.rst
+++ b/doc/releases/changes.rst
@@ -15,7 +15,7 @@ Bug Fixes
 Backward-Incompatible Changes
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Version 5.1.2 (released Oct 4, 2023)
+Version 5.1.2 (released Oct 3, 2023)
 ----------------------------------------
 
 - Update Vega-Lite from version 5.14.1 to version 5.15.1;