diff --git a/site/app.yaml b/site/app.yaml
index c0339921..837d9d01 100644
--- a/site/app.yaml
+++ b/site/app.yaml
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-runtime: go115
+runtime: go121
 service: development
 
 handlers: