diff --git a/build.json b/build.json
index 51e70d53..cc78030e 100644
--- a/build.json
+++ b/build.json
@@ -1,7 +1,7 @@
 {
   "variable": {
     "PYTHON_VERSION": {
-      "default": "3.9.13"
+      "default": "3.11.3"
     },
     "PGSQL_VERSION": {
       "default": "15"
diff --git a/stack/base/Dockerfile b/stack/base/Dockerfile
index 00257807..5b7cc270 100644
--- a/stack/base/Dockerfile
+++ b/stack/base/Dockerfile
@@ -59,12 +59,13 @@ COPY pip.conf "${CONDA_DIR}/pip.conf"
 # Upgrade pip and mamba to latest
 # Update async_generator, certipy to satisfy `pip check`
 # https://github.com/aiidalab/aiidalab-docker-stack/issues/490
+# Update zstandard, without this the `mamba install` command fails for unknown reason.
 # Install aiida-core and other shared requirements.
-RUN mamba update -y pip async_generator certipy && \
+RUN mamba update -y pip zstandard async_generator certipy && \
      mamba install --yes \
+     mamba=1.5 \
      aiida-core==${AIIDA_VERSION} \
      mamba-bash-completion \
-     traitlets=5.9.0 \
      && mamba clean --all -f -y && \
      fix-permissions "${CONDA_DIR}"
 
diff --git a/stack/lab/Dockerfile b/stack/lab/Dockerfile
index 3bcb97bd..0c2d29cd 100644
--- a/stack/lab/Dockerfile
+++ b/stack/lab/Dockerfile
@@ -77,7 +77,7 @@ WORKDIR "/home/${NB_USER}"
 
 RUN  mkdir -p /home/${NB_USER}/apps
 
-# When a Jupyter notebook server looses a connection to the frontend,
+# NOTE1: When a Jupyter notebook server looses a connection to the frontend,
 # it keeps the messages in a buffer. If there is a background thread running
 # and trying to update the frontend, the buffer grows indefinitely,
 # eventually consuming all available RAM.
@@ -87,8 +87,10 @@ RUN  mkdir -p /home/${NB_USER}/apps
 # but that may come with other problems for people with flaky internet connections.
 # Instead, here we configure Jupyter to kill all kernels that have been alive for
 # more than 12 hours. We also close all inactive terminals after 10 minutes.
+# NOTE2: show_banner=False disables the banner for upgrading to Notebook 7.
 ENV NOTEBOOK_ARGS \
      "--NotebookApp.default_url='/apps/apps/home/start.ipynb'" \
+     "--NotebookApp.show_banner=False" \
      "--ContentsManager.allow_hidden=True" \
      "--MappingKernelManager.buffer_offline_messages=True" \
      "--MappingKernelManager.cull_busy=True" \