diff --git a/.gitignore b/.gitignore
index d52b3635c..b84734b6f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -12,6 +12,7 @@ build/
 /.devcontainer
 docs*/**/_autosummary
 docs*/_build
+docs*/_collections
 docs*/**/tmp
 flaxlib_src/build
 flaxlib_src/builddir
diff --git a/docs_nnx/conf.py b/docs_nnx/conf.py
index 4b3a8c760..ac73e3f3d 100644
--- a/docs_nnx/conf.py
+++ b/docs_nnx/conf.py
@@ -65,8 +65,45 @@
   'codediff',
   'flax_module',
   'sphinx_design',
+  'sphinx_collections',
 ]
 
+# -- Sphinx-collections configuration ----------------------------------------
+# Custom function to clone optax repo and extract only the docs/api folder
+def clone_optax_api_docs(config):
+  """Clone optax repo and copy only docs/api folder."""
+  import tempfile
+  import shutil
+  from pathlib import Path
+  from git import Repo
+
+  target = Path(config['target'])
+  if target.exists():
+    return None  # Already cloned, return None to skip writing
+
+  with tempfile.TemporaryDirectory() as tmpdir:
+    Repo.clone_from(
+      'https://github.com/google-deepmind/optax.git',
+      tmpdir,
+      depth=1,
+    )
+    src = Path(tmpdir) / 'docs' / 'api'
+    shutil.copytree(src, target)
+
+  return None  # We handle file creation ourselves
+
+
+collections = {
+  'optax_api': {
+    'driver': 'function',
+    'source': clone_optax_api_docs,
+    'target': 'optax_api',  # Will be placed in _collections/optax_api
+    'write_result': False,  # We handle file creation ourselves
+    'final_clean': False,  # Keep the cloned files after build
+    'clean': False,  # Don't clean before building (we check if exists)
+  }
+}
+
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
 
diff --git a/docs_nnx/index.rst b/docs_nnx/index.rst
index b02d1ae82..296838205 100644
--- a/docs_nnx/index.rst
+++ b/docs_nnx/index.rst
@@ -200,3 +200,10 @@ Learn more
    philosophy
    contributing
    api_reference/index
+
+.. toctree::
+   :hidden:
+   :maxdepth: 2
+   :caption: Optax API
+
+   _collections/optax_api/index
diff --git a/pyproject.toml b/pyproject.toml
index 92856df13..d76983b28 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -76,6 +76,8 @@ testing = [
 docs = [
     "sphinx==6.2.1",
     "sphinx-book-theme",
+    "sphinx-collections",
+    "gitpython",
     "Pygments>=2.6.1",
     "ipykernel",
     "myst_nb",