diff --git a/swh/objstorage/api/server.py b/swh/objstorage/api/server.py
--- a/swh/objstorage/api/server.py
+++ b/swh/objstorage/api/server.py
@@ -175,8 +175,7 @@
 
     # retro compatibility configuration settings
     app["config"] = config
-    _cfg = config["objstorage"]
-    app["objstorage"] = get_objstorage(_cfg["cls"], _cfg["args"])
+    app["objstorage"] = get_objstorage(**config["objstorage"])
 
     app.router.add_route("GET", "/", index)
     app.router.add_route("POST", "/check_config", check_config)
@@ -237,20 +236,14 @@
 
     missing_keys = []
     vcfg = cfg["objstorage"]
-    for key in ("cls", "args"):
-        v = vcfg.get(key)
-        if v is None:
-            missing_keys.append(key)
-
-    if missing_keys:
-        raise KeyError(
-            "Invalid configuration; missing %s config entry"
-            % (", ".join(missing_keys),)
-        )
-
-    cls = vcfg.get("cls")
+    if "cls" not in vcfg:
+        raise KeyError("Invalid configuration; missing cls config entry")
+
+    cls = vcfg["cls"]
     if cls == "pathslicing":
-        args = vcfg["args"]
+        # Backwards-compatibility: either get the deprecated `args` from the
+        # objstorage config, or use the full config itself to check for keys
+        args = vcfg.get("args", vcfg)
         for key in ("root", "slicing"):
             v = args.get(key)
             if v is None:
@@ -258,7 +251,7 @@
 
         if missing_keys:
             raise KeyError(
-                "Invalid configuration; missing args.%s config entry"
+                "Invalid configuration; missing %s config entry"
                 % (", ".join(missing_keys),)
             )
 
diff --git a/swh/objstorage/factory.py b/swh/objstorage/factory.py
--- a/swh/objstorage/factory.py
+++ b/swh/objstorage/factory.py
@@ -4,6 +4,7 @@
 # See top-level LICENSE file for more information
 
 from typing import Callable, Dict, Union
+import warnings
 
 from swh.objstorage.api.client import RemoteObjStorage
 from swh.objstorage.backends.generator import RandomGeneratorObjStorage
@@ -59,15 +60,15 @@
     _STORAGE_CLASSES_MISSING["swift"] = e.args[0]
 
 
-def get_objstorage(cls, args):
+def get_objstorage(cls: str, args=None, **kwargs):
     """ Create an ObjStorage using the given implementation class.
 
     Args:
-        cls (str): objstorage class unique key contained in the
+        cls: objstorage class unique key contained in the
             _STORAGE_CLASSES dict.
-        args (dict): arguments for the required class of objstorage
-            that must match exactly the one in the `__init__` method of the
-            class.
+        kwargs: arguments for the required class of objstorage
+                that must match exactly the one in the `__init__` method of the
+                class.
     Returns:
         subclass of ObjStorage that match the given `storage_class` argument.
     Raises:
@@ -75,7 +76,17 @@
             key.
     """
     if cls in _STORAGE_CLASSES:
-        return _STORAGE_CLASSES[cls](**args)
+        if args is not None:
+            warnings.warn(
+                'Explicit "args" key is deprecated for objstorage initialization, '
+                "use class arguments keys directly instead.",
+                DeprecationWarning,
+            )
+            # TODO: when removing this, drop the "args" backwards compatibility
+            # from swh.objstorage.api.server configuration checker
+            kwargs = args
+
+        return _STORAGE_CLASSES[cls](**kwargs)
     else:
         raise ValueError(
             "Storage class {} is not available: {}".format(
diff --git a/swh/objstorage/tests/test_multiplexer_filter.py b/swh/objstorage/tests/test_multiplexer_filter.py
--- a/swh/objstorage/tests/test_multiplexer_filter.py
+++ b/swh/objstorage/tests/test_multiplexer_filter.py
@@ -28,12 +28,13 @@
         self.tmpdir = tempfile.mkdtemp()
         pstorage = {
             "cls": "pathslicing",
-            "args": {"root": self.tmpdir, "slicing": "0:5"},
+            "root": self.tmpdir,
+            "slicing": "0:5",
         }
         base_storage = get_objstorage(**pstorage)
         base_storage.id = compute_hash
         self.storage = get_objstorage(
-            "filtered", {"storage_conf": pstorage, "filters_conf": [read_only()]}
+            "filtered", storage_conf=pstorage, filters_conf=[read_only()]
         )
         self.valid_content = b"pre-existing content"
         self.invalid_content = b"invalid_content"
diff --git a/swh/objstorage/tests/test_objstorage_api.py b/swh/objstorage/tests/test_objstorage_api.py
--- a/swh/objstorage/tests/test_objstorage_api.py
+++ b/swh/objstorage/tests/test_objstorage_api.py
@@ -26,11 +26,9 @@
         self.config = {
             "objstorage": {
                 "cls": "pathslicing",
-                "args": {
-                    "root": self.tmpdir,
-                    "slicing": "0:1/0:5",
-                    "allow_delete": True,
-                },
+                "root": self.tmpdir,
+                "slicing": "0:1/0:5",
+                "allow_delete": True,
             },
             "client_max_size": 8 * 1024 * 1024,
         }
diff --git a/swh/objstorage/tests/test_server.py b/swh/objstorage/tests/test_server.py
--- a/swh/objstorage/tests/test_server.py
+++ b/swh/objstorage/tests/test_server.py
@@ -59,17 +59,13 @@
 
 def test_load_and_check_config_invalid_configuration(tmpdir):
     """Invalid configuration raises"""
-    for data, missing_keys in [
-        ({"objstorage": {"something": "useless"}}, ["cls", "args"]),
-        ({"objstorage": {"cls": "something"}}, ["args"]),
-    ]:
-        config_path = prepare_config_file(tmpdir, content=data)
-        with pytest.raises(KeyError) as e:
-            load_and_check_config(config_path)
+    config_path = prepare_config_file(
+        tmpdir, content={"objstorage": {"something": "useless"}}
+    )
+    with pytest.raises(KeyError) as e:
+        load_and_check_config(config_path)
 
-        assert e.value.args[0] == "Invalid configuration; missing %s config entry" % (
-            ", ".join(missing_keys),
-        )
+    assert "missing cls config entry" in e.value.args[0]
 
 
 def test_load_and_check_config_invalid_configuration_level2(tmpdir):
@@ -88,10 +84,7 @@
         with pytest.raises(KeyError) as e:
             load_and_check_config(config_path)
 
-        assert (
-            e.value.args[0]
-            == "Invalid configuration; missing args.%s config entry" % key
-        )
+        assert "missing %s config entry" % key in e.value.args[0]
 
 
 def test_load_and_check_config_fine(tmpdir):
@@ -108,8 +101,26 @@
     assert cfg == config
 
 
+def test_load_and_check_config_no_args(tmpdir):
+    """pathslicing configuration with no args key loads ok"""
+    config = {
+        "objstorage": {"cls": "pathslicing", "root": "root", "slicing": "slicing"}
+    }
+
+    config_path = prepare_config_file(tmpdir, config)
+    cfg = load_and_check_config(config_path)
+    assert cfg == config
+
+
 def test_load_and_check_config_fine2(tmpdir):
-    config = {"client_max_size": "10", "objstorage": {"cls": "remote", "args": {}}}
+    config = {"client_max_size": "10", "objstorage": {"cls": "memory", "args": {}}}
+    config_path = prepare_config_file(tmpdir, config)
+    cfg = load_and_check_config(config_path)
+    assert cfg == config
+
+
+def test_load_and_check_config_only_cls(tmpdir):
+    config = {"client_max_size": "10", "objstorage": {"cls": "memory"}}
     config_path = prepare_config_file(tmpdir, config)
     cfg = load_and_check_config(config_path)
     assert cfg == config