diff --git a/mpcontribs-client/mpcontribs/client/__init__.py b/mpcontribs-client/mpcontribs/client/__init__.py
index a71f7929f..7a8bab565 100644
--- a/mpcontribs-client/mpcontribs/client/__init__.py
+++ b/mpcontribs-client/mpcontribs/client/__init__.py
@@ -59,6 +59,8 @@
 from pint.errors import DimensionalityError
 from tempfile import gettempdir
 from plotly.express._chart_types import line as line_chart
+from cachetools import cached, LRUCache
+from cachetools.keys import hashkey
 
 RETRIES = 3
 MAX_WORKERS = 3
@@ -680,7 +682,9 @@ def _load(protocol, host, headers_json, project, version):
     projects = sorted(d["name"] for d in resp["data"])
     projects_json = ujson.dumps(projects)
     # expand regex-based query parameters for `data` columns
-    return _expand_params(protocol, host, version, projects_json)
+    spec = _expand_params(protocol, host, version, projects_json, apikey=headers["x-api-key"])
+    spec.http_client.session.headers.update(headers)
+    return spec
 
 
 @functools.lru_cache(maxsize=1)
@@ -714,15 +718,22 @@ def _raw_specs(protocol, host, version):
     return spec_dict
 
 
-@functools.lru_cache(maxsize=100)
-def _expand_params(protocol, host, version, projects_json):
+@cached(
+    cache=LRUCache(maxsize=100),
+    key=lambda protocol, host, version, projects_json, **kwargs: hashkey(
+        protocol, host, version, projects_json
+    )
+)
+def _expand_params(protocol, host, version, projects_json, apikey=None):
     columns = {"string": [], "number": []}
     projects = ujson.loads(projects_json)
-    query = {"project__in": projects}
+    query = {"project__in": ",".join(projects)}
     query["_fields"] = ["columns"]
     url = f"{protocol}://{host}"
     http_client = RequestsClient()
     http_client.session.headers["Content-Type"] = "application/json"
+    if apikey:
+        http_client.session.headers["X-Api-Key"] = apikey
     resp = http_client.session.get(f"{url}/projects/", params=query).json()
 
     for proj in resp["data"]:
diff --git a/mpcontribs-client/setup.py b/mpcontribs-client/setup.py
index bbf50728f..06f6be66a 100644
--- a/mpcontribs-client/setup.py
+++ b/mpcontribs-client/setup.py
@@ -38,6 +38,7 @@ def local_version(version):
         "tqdm",
         "ujson",
         "semantic-version",
+        "cachetools",
     ],
     extras_require={
         "dev": [