diff --git a/src/rez/package_cache.py b/src/rez/package_cache.py
index 5e9f00e26..821cb0677 100644
--- a/src/rez/package_cache.py
+++ b/src/rez/package_cache.py
@@ -366,7 +366,7 @@ def remove_variant(self, variant):
 
         return self.VARIANT_REMOVED
 
-    def add_variants_async(self, variants, _async=False):
+    def add_variants_async(self, variants, _async=True):
         """Update the package cache by adding some or all of the given variants.
 
         This method is called when a context is created or sourced. Variants
@@ -461,6 +461,8 @@ def add_variants_async(self, variants, _async=False):
                     out_target = devnull
 
                 func = subprocess.Popen
+
+                # use subprocess.call if we are not running async since it is blocking
                 if not _async:
                     func = subprocess.call