diff --git a/lib/spack/spack/__init__.py b/lib/spack/spack/__init__.py
index 1fd96b7ef5..32d8192bcb 100644
--- a/lib/spack/spack/__init__.py
+++ b/lib/spack/spack/__init__.py
@@ -4,7 +4,7 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
 #: PEP440 canonical <major>.<minor>.<micro>.<devN> string
-__version__ = "0.21.0"
+__version__ = "0.21.1.dev0"
 spack_version = __version__