diff --git a/openedx/core/djangoapps/content_libraries/tests/test_content_libraries.py b/openedx/core/djangoapps/content_libraries/tests/test_content_libraries.py
index c23679cb18..599dfd9a60 100644
--- a/openedx/core/djangoapps/content_libraries/tests/test_content_libraries.py
+++ b/openedx/core/djangoapps/content_libraries/tests/test_content_libraries.py
@@ -3,7 +3,9 @@ Tests for Blockstore-based Content Libraries
 """
 from uuid import UUID
 from unittest.mock import patch
+from urllib.parse import urlparse, parse_qsl
 
+import json
 import ddt
 from django.conf import settings
 from django.contrib.auth.models import Group
@@ -11,6 +13,9 @@ from django.test.client import Client
 from django.test.utils import override_settings
 from organizations.models import Organization
 from rest_framework.test import APITestCase
+from web_fragments.fragment import Fragment
+from webob import Response
+from xblock.core import XBlock
 
 from openedx.core.djangoapps.content_libraries.libraries_index import LibraryBlockIndexer, ContentLibraryIndexer
 from openedx.core.djangoapps.content_libraries.tests.base import (
@@ -20,6 +25,7 @@ from openedx.core.djangoapps.content_libraries.tests.base import (
     URL_BLOCK_RENDER_VIEW,
     URL_BLOCK_GET_HANDLER_URL,
     URL_BLOCK_XBLOCK_HANDLER,
+    URL_LIB_BLOCK_OLX,
 )
 from openedx.core.djangoapps.content_libraries.constants import VIDEO, COMPLEX, PROBLEM, CC_4_BY, ALL_RIGHTS_RESERVED
 from openedx.core.djangolib.blockstore_cache import cache
@@ -903,3 +909,164 @@ class ContentLibraryXBlockValidationTest(APITestCase):
         self.assertEqual(response.json(), {
             'detail': f"XBlock {valid_not_found_key} does not exist, or you don't have permission to view it.",
         })
+
+
+class AltBlock(XBlock):
+    """Class for testing LabXchange XBlock type overrides."""
+    @XBlock.handler
+    def student_view_user_state(self, request, suffix=""):
+        """
+        Returns a JSON response for testing.
+        """
+        view_state = {
+            "id": str(self.location),
+            "block_type": str(self.location.block_type),
+            "override_type": str(self.__class__),
+        }
+        return Response(
+            json.dumps(view_state),
+            content_type='application/json',
+            charset='UTF-8',
+        )
+
+    def student_view(self, context=None):
+        """
+        Returns an HTML fragment for testing.
+        """
+        return Fragment(f"<div data-usage='{self.location}' data-block-type='{self.location.block_type}'>"
+                        "<div class='AltBlock-wrapper'/></div>")
+
+
+@ddt.ddt
+@elasticsearch_test
+class ContentLibrariesXBlockTypeOverrideTest(ContentLibrariesRestApiTest):
+    """
+    Tests for Blockstore-based Content Libraries XBlock API,
+    where the expected XBlock type returned is overridden in the request.
+    """
+    BLOCK_DATA = (
+        ('block-wo-override', {}, 'video'),
+        ('block-w-override', {'lx_block_types': '1'}, 'alt-block'),
+    )
+
+    def setUp(self):
+        super().setUp()
+        if settings.ENABLE_ELASTICSEARCH_FOR_TESTS:
+            ContentLibraryIndexer.remove_all_items()
+            LibraryBlockIndexer.remove_all_items()
+
+        self.olx = """
+        <video display_name="Test Block Type Overrides"
+            youtube_id_1_0="rE42zZ-3wNo"
+            transcripts="{&quot;en&quot;: &quot;transcript.srt&quot;}" />
+        """.strip()
+
+    def create_block(self, slug, block_type='video'):
+        """
+        Add a new library containing a block, using the given slug to keep them unique.
+        """
+        lib = self._create_library(slug=slug, title='Test Block Type Overrides', library_type=COMPLEX)
+        block = self._add_block_to_library(lib['id'], block_type, slug)
+        self._set_library_block_olx(block['id'], self.olx)
+        self._commit_library_changes(lib['id'])
+        return block['id']
+
+    @ddt.data(*BLOCK_DATA)
+    @ddt.unpack
+    @patch("openedx.core.djangoapps.xblock.rest_api.views.LX_BLOCK_TYPES_OVERRIDE", {'video': 'alt-block'})
+    @XBlock.register_temp_plugin(AltBlock, 'alt-block')
+    def test_block_type_metadata(self, slug, api_args, expected_type):
+        """
+        Check that the metadata API returns the overridden block type.
+        """
+        block_key = self.create_block(f"metadata-{slug}")
+        response = self.client.get(
+            URL_BLOCK_METADATA_URL.format(block_key=block_key),
+            api_args,
+        )
+        assert response.data['block_id'] == str(block_key)
+        assert response.data['block_type'] == expected_type
+        assert response.data['display_name'] == 'Test Block Type Overrides'
+
+    @ddt.data(*BLOCK_DATA)
+    @ddt.unpack
+    @patch("openedx.core.djangoapps.xblock.rest_api.views.LX_BLOCK_TYPES_OVERRIDE", {'video': 'alt-block'})
+    @XBlock.register_temp_plugin(AltBlock, 'alt-block')
+    def test_block_type_olx(self, slug, api_args, expected_type):
+        """
+        Check that the OLX API is unchanged when overriding the block type.
+        """
+        block_key = self.create_block(f"olx-{slug}")
+        response = self.client.get(
+            URL_LIB_BLOCK_OLX.format(block_key=block_key),
+            api_args,
+        )
+        assert response.data['olx'] == self.olx
+
+    @ddt.data(*BLOCK_DATA)
+    @ddt.unpack
+    @patch("openedx.core.djangoapps.xblock.rest_api.views.LX_BLOCK_TYPES_OVERRIDE", {'video': 'alt-block'})
+    @XBlock.register_temp_plugin(AltBlock, 'alt-block')
+    def test_block_type_render(self, slug, api_args, expected_type):
+        """
+        Check that the rendered block HTML uses the overridden block type.
+        """
+        block_key = self.create_block(f"render-{slug}")
+        response = self.client.get(
+            URL_BLOCK_RENDER_VIEW.format(block_key=block_key, view_name='student_view'),
+            api_args,
+        )
+        assert response.data['block_id'] == str(block_key)
+        assert response.data['block_type'] == expected_type
+        assert response.data['display_name'] == 'Test Block Type Overrides'
+        assert f"data-usage='{block_key}'" in response.data['content']
+        assert f"data-block-type='{expected_type}'" in response.data['content']
+        if expected_type == 'video':
+            assert 'class="video-wrapper"' in response.data['content']
+        else:
+            assert "class='AltBlock-wrapper'" in response.data['content']
+
+    @ddt.data(*BLOCK_DATA)
+    @ddt.unpack
+    @patch("openedx.core.djangoapps.xblock.rest_api.views.LX_BLOCK_TYPES_OVERRIDE", {'video': 'alt-block'})
+    @XBlock.register_temp_plugin(AltBlock, 'alt-block')
+    def test_block_type_handler(self, slug, api_args, expected_type):
+        # Check that the handler_url contains the block type override params
+        block_key = self.create_block(f"handler-{slug}")
+        response = self.client.get(
+            URL_BLOCK_GET_HANDLER_URL.format(block_key=block_key, handler_name='student_view_user_state'),
+            api_args,
+        )
+        handler_url = response.data['handler_url']
+        parsed_url = urlparse(handler_url)
+        parsed_qs = dict(parse_qsl(parsed_url.query))
+        assert parsed_qs == api_args
+
+        # Ensure the invoked handler hits the expected Block
+        if expected_type == 'video':
+            expected_response = {
+                'all_sources': [],
+                'duration': None,
+                'encoded_videos': {
+                    'youtube': {
+                        'file_size': 0,
+                        'url': 'https://www.youtube.com/watch?v=rE42zZ-3wNo',
+                    }
+                },
+                'only_on_web': False,
+                'saved_video_position': 0.0,
+                'speed': None,
+                'transcripts': {},
+            }
+        else:
+            expected_response = {
+                "id": f'lb:CL-TEST:handler-{slug}:video:handler-{slug}',
+                "block_type": 'video',
+                "override_type": "<class 'xblock.internal.AltBlockWithMixins'>",
+            }
+        response = self.client.post(handler_url).json()
+        # Can't match the Transcripts download URL exactly, but we can check that it's there and roughly correct
+        if 'transcripts' in response:
+            assert f"lb:CL-TEST:handler-{slug}:video:handler-{slug}" in response['transcripts']['en']
+            del response['transcripts']['en']
+        assert response == expected_response
diff --git a/openedx/core/djangoapps/xblock/api.py b/openedx/core/djangoapps/xblock/api.py
index 60b8a1e13b..d55d634917 100644
--- a/openedx/core/djangoapps/xblock/api.py
+++ b/openedx/core/djangoapps/xblock/api.py
@@ -10,6 +10,7 @@ Studio APIs cover use cases like adding/deleting/editing blocks.
 
 import logging
 import threading
+from urllib.parse import urlencode
 
 from django.urls import reverse
 from django.utils.translation import gettext as _
@@ -58,7 +59,7 @@ def get_runtime_system():
     return getattr(get_runtime_system, cache_name)
 
 
-def load_block(usage_key, user):
+def load_block(usage_key, user, block_type_overrides=None):
     """
     Load the specified XBlock for the given user.
 
@@ -67,6 +68,12 @@ def load_block(usage_key, user):
     Exceptions:
         NotFound - if the XBlock doesn't exist or if the user doesn't have the
                    necessary permissions
+
+    Args:
+        usage_key(OpaqueKey): block identifier
+        user(User): user requesting the block
+        block_type_overrides(dict): optional dict of block types to override in returned block metadata:
+            {'from_block_type': 'to_block_type'}
     """
     # Is this block part of a course, a library, or what?
     # Get the Learning Context Implementation based on the usage key
@@ -85,7 +92,7 @@ def load_block(usage_key, user):
 
     runtime = get_runtime_system().get_runtime(user=user)
 
-    return runtime.get_block(usage_key)
+    return runtime.get_block(usage_key, block_type_overrides=block_type_overrides)
 
 
 def get_block_metadata(block, includes=()):
@@ -215,7 +222,7 @@ def render_block_view(block, view_name, user):  # pylint: disable=unused-argumen
     return fragment
 
 
-def get_handler_url(usage_key, handler_name, user):
+def get_handler_url(usage_key, handler_name, user, extra_params=None):
     """
     A method for getting the URL to any XBlock handler. The URL must be usable
     without any authentication (no cookie, no OAuth/JWT), and may expire. (So
@@ -232,6 +239,7 @@ def get_handler_url(usage_key, handler_name, user):
         usage_key       - Usage Key (Opaque Key object or string)
         handler_name    - Name of the handler or a dummy name like 'any_handler'
         user            - Django User (registered or anonymous)
+        extra_params    - Optional extra params to append to the handler_url (dict)
 
     This view does not check/care if the XBlock actually exists.
     """
@@ -255,8 +263,11 @@ def get_handler_url(usage_key, handler_name, user):
         'secure_token': secure_token,
         'handler_name': handler_name,
     })
+    qstring = urlencode(extra_params) if extra_params else ''
+    if qstring:
+        qstring = '?' + qstring
     # We must return an absolute URL. We can't just use
     # rest_framework.reverse.reverse to get the absolute URL because this method
     # can be called by the XBlock from python as well and in that case we don't
     # have access to the request.
-    return site_root_url + path
+    return site_root_url + path + qstring
diff --git a/openedx/core/djangoapps/xblock/rest_api/views.py b/openedx/core/djangoapps/xblock/rest_api/views.py
index 024b8baf42..520fee8d7f 100644
--- a/openedx/core/djangoapps/xblock/rest_api/views.py
+++ b/openedx/core/djangoapps/xblock/rest_api/views.py
@@ -29,11 +29,31 @@ from ..utils import validate_secure_token_for_xblock_handler
 
 User = get_user_model()
 
+LX_BLOCK_TYPES_OVERRIDE = {
+    'problem': 'lx_question',
+    'video': 'lx_video',
+    'html': 'lx_html',
+}
+
 
 class InvalidNotFound(NotFound):
     default_detail = "Invalid XBlock key"
 
 
+def _block_type_overrides(request_args):
+    """
+    If the request contains the argument `lx_block_types=1`, then
+    returns a dict of LabXchange block types, which override the default block types.
+
+    Otherwise, returns None.
+
+    FYI: This is a temporary change, added to assist LabXchange with the transition to using their custom runtime.
+    """
+    if request_args.get('lx_block_types'):
+        return LX_BLOCK_TYPES_OVERRIDE
+    return None
+
+
 @api_view(['GET'])
 @view_auth_classes(is_authenticated=False)
 @permission_classes((permissions.AllowAny, ))  # Permissions are handled at a lower level, by the learning context
@@ -41,15 +61,19 @@ def block_metadata(request, usage_key_str):
     """
     Get metadata about the specified block.
 
-    Accepts an "include" query parameter which must be a comma separated list of keys to include. Valid keys are
-    "index_dictionary" and "student_view_data".
+    Accepts the following query parameters:
+
+    * "include": a comma-separated list of keys to include.
+      Valid keys are "index_dictionary" and "student_view_data".
+    * "lx_block_types": optional boolean; set to use the LabXchange XBlock classes to load the requested block.
+      The block ID and OLX remain unchanged; they will use the original block type.
     """
     try:
         usage_key = UsageKey.from_string(usage_key_str)
     except InvalidKeyError as e:
         raise InvalidNotFound from e
 
-    block = load_block(usage_key, request.user)
+    block = load_block(usage_key, request.user, block_type_overrides=_block_type_overrides(request.GET))
     includes = request.GET.get("include", "").split(",")
     metadata_dict = get_block_metadata(block, includes=includes)
     if 'children' in metadata_dict:
@@ -65,13 +89,17 @@ def block_metadata(request, usage_key_str):
 def render_block_view(request, usage_key_str, view_name):
     """
     Get the HTML, JS, and CSS needed to render the given XBlock.
+
+    Accepts the following query parameters:
+    * "lx_block_types": optional boolean; set to use the LabXchange XBlock classes to load the requested block.
+      The block ID and OLX remain unchanged; they will use the original block type.
     """
     try:
         usage_key = UsageKey.from_string(usage_key_str)
     except InvalidKeyError as e:
         raise InvalidNotFound from e
 
-    block = load_block(usage_key, request.user)
+    block = load_block(usage_key, request.user, block_type_overrides=_block_type_overrides(request.GET))
     fragment = _render_block_view(block, view_name, request.user)
     response_data = get_block_metadata(block)
     response_data.update(fragment.to_dict())
@@ -86,13 +114,17 @@ def get_handler_url(request, usage_key_str, handler_name):
     the given XBlock handler.
 
     The URL will expire but is guaranteed to be valid for a minimum of 2 days.
+
+    The following query parameters will be appended to the returned handler_url:
+    * "lx_block_types": optional boolean; set to use the LabXchange XBlock classes to load the requested block.
+      The block ID and OLX remain unchanged; they will use the original block type.
     """
     try:
         usage_key = UsageKey.from_string(usage_key_str)
     except InvalidKeyError as e:
         raise InvalidNotFound from e
 
-    handler_url = _get_handler_url(usage_key, handler_name, request.user)
+    handler_url = _get_handler_url(usage_key, handler_name, request.user, request.GET)
     return Response({"handler_url": handler_url})
 
 
@@ -109,6 +141,11 @@ def xblock_handler(request, user_id, secure_token, usage_key_str, handler_name,
     This endpoint has a unique authentication scheme that involves a temporary
     auth token included in the URL (see below). As a result it can be exempt
     from CSRF, session auth, and JWT/OAuth.
+
+    Accepts the following query parameters (in addition to those passed to the handler):
+
+    * "lx_block_types": optional boolean; set to use the LabXchange XBlock classes to load the requested block.
+      The block ID and OLX remain unchanged; they will use the original block type.
     """
     try:
         usage_key = UsageKey.from_string(usage_key_str)
@@ -149,7 +186,7 @@ def xblock_handler(request, user_id, secure_token, usage_key_str, handler_name,
         raise AuthenticationFailed("Invalid user ID format.")
 
     request_webob = DjangoWebobRequest(request)  # Convert from django request to the webob format that XBlocks expect
-    block = load_block(usage_key, user)
+    block = load_block(usage_key, user, block_type_overrides=_block_type_overrides(request.GET))
     # Run the handler, and save any resulting XBlock field value changes:
     response_webob = block.handle(handler_name, request_webob, suffix)
     response = webob_to_django_response(response_webob)
diff --git a/openedx/core/djangoapps/xblock/runtime/blockstore_runtime.py b/openedx/core/djangoapps/xblock/runtime/blockstore_runtime.py
index dcb59b1e6d..f48ae7d0b8 100644
--- a/openedx/core/djangoapps/xblock/runtime/blockstore_runtime.py
+++ b/openedx/core/djangoapps/xblock/runtime/blockstore_runtime.py
@@ -33,11 +33,14 @@ class BlockstoreXBlockRuntime(XBlockRuntime):
     def parse_xml_file(self, fileobj, id_generator=None):
         raise NotImplementedError("Use parse_olx_file() instead")
 
-    def get_block(self, usage_id, for_parent=None):
+    def get_block(self, usage_id, for_parent=None, block_type_overrides=None):  # pylint: disable=arguments-differ
         """
         Create an XBlock instance in this runtime.
 
-        The `usage_id` is used to find the XBlock class and data.
+        Args:
+            usage_key(OpaqueKey): identifier used to find the XBlock class and data.
+            block_type_overrides(dict): optional dict of block types to override in returned block metadata:
+                {'from_block_type': 'to_block_type'}
         """
         def_id = self.id_reader.get_definition_id(usage_id)
         if def_id is None:
@@ -46,6 +49,8 @@ class BlockstoreXBlockRuntime(XBlockRuntime):
             raise TypeError("This runtime can only load blocks stored in Blockstore bundles.")
         try:
             block_type = self.id_reader.get_block_type(def_id)
+            if block_type_overrides and block_type in block_type_overrides:
+                block_type = block_type_overrides[block_type]
         except NoSuchDefinition:
             raise NoSuchUsage(repr(usage_id))  # lint-amnesty, pylint: disable=raise-missing-from
         keys = ScopeIds(self.user_id, block_type, def_id, usage_id)