diff --git a/.github/actions/setup-bo4e/action.yml b/.github/actions/setup-bo4e/action.yml
index 558f611a2..c6d758b3a 100644
--- a/.github/actions/setup-bo4e/action.yml
+++ b/.github/actions/setup-bo4e/action.yml
@@ -5,7 +5,9 @@ inputs:
   version:
     description: bo4e CLI release tag to install.
     required: false
-    default: v1.2.3
+    # v1.2.4 is the first release with the `{class.lower}` link-template
+    # accessor that the docs asset script relies on for correct API-doc anchors.
+    default: v1.2.4
 
 runs:
   using: composite
diff --git a/docs/_templates/layout.html b/docs/_templates/layout.html
new file mode 100644
index 000000000..8001c93a6
--- /dev/null
+++ b/docs/_templates/layout.html
@@ -0,0 +1,45 @@
+{% extends "!layout.html" %}
+
+{#-
+  sphinx-rtd-theme 3.1.0 removed the always-on sidebar version string. Earlier
+  releases (<= 3.0.2) rendered `<div class="version">{{ version }}</div>` under
+  the project name via the `display_version` option; 3.1.0 replaced it with a
+  version switcher that only renders on Read the Docs hosting (the
+  `READTHEDOCS or DEBUG` gate). These docs are deployed to GitHub Pages, where
+  that gate is never true, so the version disappeared entirely.
+
+  We override the theme's `sidebartitle` block to restore the classic version
+  div. The rest of the block mirrors sphinx-rtd-theme 3.1.0's `layout.html`
+  (pinned in docs/requirements.txt) so the logo, RTD switcher and search box
+  keep working. `version` is set in conf.py (SPHINX_DOCS_VERSION or the package
+  version).
+-#}
+{%- block sidebartitle %}
+
+  {%- set _logo_url = logo_url|default(pathto('_static/' + (logo or ""), 1)) %}
+  {%- set _root_doc = root_doc|default(master_doc) %}
+  <a href="{{ pathto(_root_doc) }}"{% if not theme_logo_only %} class="icon icon-home"{% endif %}>
+    {% if not theme_logo_only %}{{ project }}{% endif %}
+    {%- if logo or logo_url %}
+      <img src="{{ _logo_url }}" class="logo" alt="{{ _('Logo') }}"/>
+    {%- endif %}
+  </a>
+
+  {%- if version %}
+    <div class="version">
+      {{ version }}
+    </div>
+  {%- endif %}
+
+  {%- if READTHEDOCS or DEBUG %}
+    {%- if theme_version_selector or theme_language_selector %}
+      <div class="switch-menus">
+        <div class="version-switch"></div>
+        <div class="language-switch"></div>
+      </div>
+    {%- endif %}
+  {%- endif %}
+
+  {%- include "searchbox.html" %}
+
+{%- endblock %}
diff --git a/scripts/generate_docs_assets.py b/scripts/generate_docs_assets.py
index 4ecc6a00c..fb93d33f8 100644
--- a/scripts/generate_docs_assets.py
+++ b/scripts/generate_docs_assets.py
@@ -446,10 +446,21 @@ def _describe(env_name: str) -> str:
     is_dirty = bool(_DIRTY_RE.search(gh_version))
     docs_label = DOCS_LABEL_OVERRIDE or gh_version
 
+    # Sphinx documents each class on its Python-package page under a module
+    # anchor: `<namespace>.html#module-<namespace>.<module-file>`, where the
+    # module file is the class name lowercased (BO4E convention). `{namespace}`
+    # (bo4e-cli >= v1.2.4) is `bo4e` + the module's parent package -- `bo4e.com`
+    # for a nested schema, plain `bo4e` for a root-level one like ZusatzAttribut
+    # -- so one template covers both (the old `{module}` placeholder expanded to
+    # the schema-derived `com.Angebotsteil`, pointing at a non-existent
+    # `api/com.Angebotsteil.html`, a 404). `{namespace}` / `{class}` are expanded
+    # per-node by the CLI; only `{docs_label}` and the local path are
+    # interpolated here.
+    anchor = "{namespace}.html#module-{namespace}.{class.lower}"
     if DOCS_LABEL_OVERRIDE or not is_dirty:
-        link_template = f"https://bo4e.github.io/BO4E-python/{docs_label}/api/{{module}}.html"
+        link_template = f"https://bo4e.github.io/BO4E-python/{docs_label}/api/{anchor}"
     else:
-        link_template = f"file://{REPO_ROOT.as_posix()}/.tox/docs/tmp/html/api/{{module}}.html"
+        link_template = f"file://{REPO_ROOT.as_posix()}/.tox/docs/tmp/html/api/{anchor}"
 
     print(f"[graph] docs label:    {docs_label}")
     print(f"[graph] link template: {link_template}")