diff --git a/docs/user/index.rst b/docs/user/index.rst
index 617e8b30571..11e2c10a45a 100644
--- a/docs/user/index.rst
+++ b/docs/user/index.rst
@@ -51,6 +51,7 @@ Read the Docs: documentation simplified
    /reference/cdn
    /reference/sitemaps
    /reference/404-not-found
+   /reference/llms
    /reference/robots
 
 .. toctree::
diff --git a/docs/user/reference/features.rst b/docs/user/reference/features.rst
index b6bf1884c1b..a62754aaa6b 100644
--- a/docs/user/reference/features.rst
+++ b/docs/user/reference/features.rst
@@ -59,6 +59,11 @@ Feature reference
   We provide a default 404 page,
   but you can also customize it.
 
+⏩️ :doc:`/reference/llms`
+  ``llms.txt`` files communicate expectations to LLM-focused crawlers.
+  We provide a default file,
+  but you can also customize it.
+
 ⏩️ :doc:`/reference/robots`
   `robots.txt` files allow you to customize how your documentation is indexed in search engines.
   We provide a default robots.txt file,
diff --git a/docs/user/reference/llms.rst b/docs/user/reference/llms.rst
new file mode 100644
index 00000000000..457485538a5
--- /dev/null
+++ b/docs/user/reference/llms.rst
@@ -0,0 +1,54 @@
+``llms.txt`` support
+====================
+
+The `llms.txt` files describe how large language model crawlers can use your documentation.
+They're useful for:
+
+* Signaling which parts of your site should be avoided by AI-focused crawlers.
+* Documenting how models can attribute your content.
+* Sharing links (like a sitemap) that help LLM-powered crawlers discover content responsibly.
+
+Read the Docs automatically generates one for you with a configuration that works for most projects.
+By default, the automatically created ``llms.txt``:
+
+* Hides versions which are set to :ref:`Hidden <versions:Version states>` from being indexed by LLM crawlers.
+* Allows crawling of all other versions.
+
+.. warning::
+
+   ``llms.txt`` files are a signal to cooperating crawlers,
+   but they aren't a guarantee that your pages will not be ingested.
+   If you require *private* documentation, please see :doc:`/commercial/sharing`.
+
+How it works
+------------
+
+You can customize this file to add more rules to it.
+The ``llms.txt`` file will be served from the **default version** of your project.
+This is because the ``llms.txt`` file is served at the top-level of your domain,
+so we must choose a version to find the file in.
+The **default version** is the best place to look for it.
+
+Tool integration
+----------------
+
+Documentation tools will have different ways of generating an ``llms.txt`` file.
+We have examples for some of the most popular tools below.
+
+.. tabs::
+
+   .. tab:: Sphinx
+
+      Sphinx uses the `html_extra_path`_ configuration value to add static files to its final HTML output.
+      You need to create a ``llms.txt`` file and put it under the path defined in ``html_extra_path``.
+
+   .. tab:: MkDocs
+
+      MkDocs needs the ``llms.txt`` to be at the directory defined by the `docs_dir`_ configuration value.
+
+.. _html_extra_path: https://www.sphinx-doc.org/en/master/usage/configuration.html#confval-html_extra_path
+.. _docs_dir: https://www.mkdocs.org/user-guide/configuration/#docs_dir
+
+.. seealso::
+
+   :doc:`/reference/robots`
diff --git a/readthedocs/proxito/README.rst b/readthedocs/proxito/README.rst
index f6b76033130..d4f5894754a 100644
--- a/readthedocs/proxito/README.rst
+++ b/readthedocs/proxito/README.rst
@@ -144,6 +144,8 @@ What can/can't be cached?
 
 - ServeRobotsTXT: can be cached, we don't serve a custom robots.txt
   to any user if the default version is private.
+- ServeLLMSTXT: can be cached, we don't serve a custom llms.txt
+  to any user if the default version is private.
 - ServeSitemapXML: can be cached. It displays only public versions, for everyone.
 - ServeStaticFiles: can be cached, all files are the same for all projects and users.
 - Embed API: can be cached for public versions.
diff --git a/readthedocs/proxito/tests/base.py b/readthedocs/proxito/tests/base.py
index 869a54fe994..5bbaf4003f2 100644
--- a/readthedocs/proxito/tests/base.py
+++ b/readthedocs/proxito/tests/base.py
@@ -6,6 +6,7 @@
 from django.contrib.auth.models import User
 from readthedocs.storage import get_storage_class
 from django.test import TestCase
+from django.test.utils import override_settings
 
 from readthedocs.builds.constants import LATEST
 from readthedocs.projects.constants import PUBLIC, SSL_STATUS_VALID
@@ -13,8 +14,16 @@
 from readthedocs.proxito.views import serve
 
 
+proxito_middleware = list(settings.MIDDLEWARE) + [
+    "readthedocs.proxito.middleware.ProxitoMiddleware",
+]
+
+
 @pytest.mark.proxito
+@override_settings(ROOT_URLCONF="readthedocs.proxito.urls", MIDDLEWARE=proxito_middleware)
 class BaseDocServing(TestCase):
+    urls = "readthedocs.proxito.urls"
+
     def setUp(self):
         # Re-initialize storage
         # Various tests override either this setting or various aspects of the storage engine
diff --git a/readthedocs/proxito/tests/test_full.py b/readthedocs/proxito/tests/test_full.py
index 02486647143..853fe9c5f7d 100644
--- a/readthedocs/proxito/tests/test_full.py
+++ b/readthedocs/proxito/tests/test_full.py
@@ -952,6 +952,44 @@ def test_custom_robots_txt_private_version(self):
         )
         self.assertEqual(response.status_code, 404)
 
+    @mock.patch.object(BuildMediaFileSystemStorageTest, "exists")
+    def test_default_llms_txt(self, storage_exists):
+        storage_exists.return_value = False
+        self.project.versions.update(active=True, built=True)
+        response = self.client.get(
+            reverse("llms_txt"), headers={"host": "project.readthedocs.io"}
+        )
+        self.assertEqual(response.status_code, 200)
+        expected = dedent(
+            """
+            User-agent: *
+
+            Disallow: # Allow everything
+
+            Sitemap: https://project.readthedocs.io/sitemap.xml
+            """
+        ).lstrip()
+        self.assertContains(response, expected)
+
+    def test_custom_llms_txt(self):
+        self.project.versions.update(active=True, built=True)
+        response = self.client.get(
+            reverse("llms_txt"), headers={"host": "project.readthedocs.io"}
+        )
+        self.assertEqual(
+            response["x-accel-redirect"],
+            "/proxito/media/html/project/latest/llms.txt",
+        )
+
+    def test_custom_llms_txt_private_version(self):
+        self.project.versions.update(
+            active=True, built=True, privacy_level=constants.PRIVATE
+        )
+        response = self.client.get(
+            reverse("llms_txt"), headers={"host": "project.readthedocs.io"}
+        )
+        self.assertEqual(response.status_code, 404)
+
     def test_directory_indexes(self):
         self.project.versions.update(active=True, built=True)
 
diff --git a/readthedocs/proxito/tests/test_headers.py b/readthedocs/proxito/tests/test_headers.py
index 3ebfd019ef5..a791c50bb4d 100644
--- a/readthedocs/proxito/tests/test_headers.py
+++ b/readthedocs/proxito/tests/test_headers.py
@@ -346,6 +346,15 @@ def test_cache_headers_robots_txt_with_private_projects_not_allowed(self):
         self.assertEqual(r["CDN-Cache-Control"], "public")
         self.assertEqual(r["Cache-Tag"], "project,project:robots.txt")
 
+    @override_settings(ALLOW_PRIVATE_REPOS=False)
+    def test_cache_headers_llms_txt_with_private_projects_not_allowed(self):
+        r = self.client.get(
+            "/llms.txt", secure=True, headers={"host": "project.dev.readthedocs.io"}
+        )
+        self.assertEqual(r.status_code, 200)
+        self.assertEqual(r["CDN-Cache-Control"], "public")
+        self.assertEqual(r["Cache-Tag"], "project,project:llms.txt")
+
     @override_settings(ALLOW_PRIVATE_REPOS=True)
     def test_cache_headers_robots_txt_with_private_projects_allowed(self):
         r = self.client.get(
@@ -355,6 +364,15 @@ def test_cache_headers_robots_txt_with_private_projects_allowed(self):
         self.assertEqual(r["CDN-Cache-Control"], "public")
         self.assertEqual(r["Cache-Tag"], "project,project:robots.txt")
 
+    @override_settings(ALLOW_PRIVATE_REPOS=True)
+    def test_cache_headers_llms_txt_with_private_projects_allowed(self):
+        r = self.client.get(
+            "/llms.txt", secure=True, headers={"host": "project.dev.readthedocs.io"}
+        )
+        self.assertEqual(r.status_code, 200)
+        self.assertEqual(r["CDN-Cache-Control"], "public")
+        self.assertEqual(r["Cache-Tag"], "project,project:llms.txt")
+
     @override_settings(ALLOW_PRIVATE_REPOS=False)
     def test_cache_headers_robots_txt_with_private_projects_not_allowed(self):
         r = self.client.get(
diff --git a/readthedocs/proxito/urls.py b/readthedocs/proxito/urls.py
index 94ebe6ed46f..fc016af9fae 100644
--- a/readthedocs/proxito/urls.py
+++ b/readthedocs/proxito/urls.py
@@ -47,6 +47,7 @@
 from readthedocs.proxito.views.hosting import ReadTheDocsConfigJson
 from readthedocs.proxito.views.serve import ServeDocs
 from readthedocs.proxito.views.serve import ServeError404
+from readthedocs.proxito.views.serve import ServeLLMSTXT
 from readthedocs.proxito.views.serve import ServePageRedirect
 from readthedocs.proxito.views.serve import ServeRobotsTXT
 from readthedocs.proxito.views.serve import ServeSitemapXML
@@ -133,6 +134,7 @@
         name="proxito_404_handler",
     ),
     re_path(r"robots\.txt$", ServeRobotsTXT.as_view(), name="robots_txt"),
+    re_path(r"llms\.txt$", ServeLLMSTXT.as_view(), name="llms_txt"),
     re_path(r"sitemap\.xml$", ServeSitemapXML.as_view(), name="sitemap_xml"),
 ]
 
diff --git a/readthedocs/proxito/views/serve.py b/readthedocs/proxito/views/serve.py
index 085b714d082..38db34f7c6e 100644
--- a/readthedocs/proxito/views/serve.py
+++ b/readthedocs/proxito/views/serve.py
@@ -736,6 +736,107 @@ class ServeRobotsTXT(SettingsOverrideObject):
     _default_class = ServeRobotsTXTBase
 
 
+class ServeLLMSTXTBase(CDNCacheControlMixin, CDNCacheTagsMixin, ServeDocsMixin, View):
+    """Serve llms.txt from the domain's root."""
+
+    cache_response = True
+    project_cache_tag = "llms.txt"
+
+    def get(self, request):
+        """
+        Serve custom user's defined ``/llms.txt``.
+
+        If the project is delisted or is a spam project, we force a special llms.txt.
+
+        If the user added a ``llms.txt`` in the "default version" of the
+        project, we serve it directly.
+        """
+
+        project = request.unresolved_domain.project
+
+        if project.delisted:
+            return render(
+                request,
+                "llms.delisted.txt",
+                content_type="text/plain",
+            )
+
+        if "readthedocsext.spamfighting" in settings.INSTALLED_APPS:
+            from readthedocsext.spamfighting.utils import is_robotstxt_denied  # noqa
+
+            if is_robotstxt_denied(project):
+                return render(
+                    request,
+                    "llms.spam.txt",
+                    content_type="text/plain",
+                )
+
+        version_slug = project.get_default_version()
+        version = project.versions.get(slug=version_slug)
+
+        no_serve_llms_txt = any(
+            [
+                version.privacy_level == PRIVATE,
+                not version.active,
+                not version.built,
+            ]
+        )
+
+        if no_serve_llms_txt:
+            raise Http404()
+
+        structlog.contextvars.bind_contextvars(
+            project_slug=project.slug,
+            version_slug=version.slug,
+        )
+
+        try:
+            response = self._serve_docs(
+                request=request,
+                project=project,
+                version=version,
+                filename="llms.txt",
+                check_if_exists=True,
+            )
+            log.info("Serving custom llms.txt file.")
+            return response
+        except StorageFileNotFound:
+            pass
+
+        sitemap_url = "{scheme}://{domain}/sitemap.xml".format(
+            scheme="https",
+            domain=project.subdomain(),
+        )
+        context = {
+            "sitemap_url": sitemap_url,
+            "hidden_paths": self._get_hidden_paths(project),
+        }
+        return render(
+            request,
+            "llms.txt",
+            context,
+            content_type="text/plain",
+        )
+
+    def _get_hidden_paths(self, project):
+        hidden_versions = project.versions(manager=INTERNAL).public().filter(hidden=True)
+        resolver = Resolver()
+        hidden_paths = [
+            resolver.resolve_path(project, version_slug=version.slug) for version in hidden_versions
+        ]
+        return hidden_paths
+
+    def _get_project(self):
+        return self.request.unresolved_domain.project
+
+    def _get_version(self):
+        return None
+
+
+class ServeLLMSTXT(SettingsOverrideObject):
+    _default_class = ServeLLMSTXTBase
+
+
 class ServeSitemapXMLBase(CDNCacheControlMixin, CDNCacheTagsMixin, View):
     """Serve sitemap.xml from the domain's root."""
 
diff --git a/readthedocs/templates/llms.delisted.txt b/readthedocs/templates/llms.delisted.txt
new file mode 100644
index 00000000000..279b872c434
--- /dev/null
+++ b/readthedocs/templates/llms.delisted.txt
@@ -0,0 +1,4 @@
+# Delisted project, blocking large language model crawlers
+# See: https://docs.readthedocs.io/en/stable/unofficial-projects.html
+User-agent: *
+Disallow: /
diff --git a/readthedocs/templates/llms.spam.txt b/readthedocs/templates/llms.spam.txt
new file mode 100644
index 00000000000..7e2fe691dc7
--- /dev/null
+++ b/readthedocs/templates/llms.spam.txt
@@ -0,0 +1,3 @@
+# Spam project detected, blocking large language model crawlers
+User-agent: *
+Disallow: /
diff --git a/readthedocs/templates/llms.txt b/readthedocs/templates/llms.txt
new file mode 100644
index 00000000000..289b359a429
--- /dev/null
+++ b/readthedocs/templates/llms.txt
@@ -0,0 +1,15 @@
+# This llms.txt file is autogenerated by Read the Docs.
+# It describes how large language model crawlers can use your documentation.
+#
+# You can learn more about llms.txt, including how to customize it, in our documentation:
+#
+# * Our documentation on llms.txt: https://docs.readthedocs.com/platform/stable/reference/llms.html
+# * Our guide about SEO techniques: https://docs.readthedocs.com/platform/stable/guides/technical-docs-seo-guide.html
+
+User-agent: *
+{% for path in hidden_paths %}
+Disallow: {{ path }} # Hidden version
+{% empty %}
+Disallow: # Allow everything
+{% endfor %}
+Sitemap: {{ sitemap_url }}