diff --git a/swh/core/api/serializers.py b/swh/core/api/serializers.py
--- a/swh/core/api/serializers.py
+++ b/swh/core/api/serializers.py
@@ -282,16 +282,6 @@
             if decoder:
                 return decoder(obj[b"d"])
 
-        # Support for legacy encodings
-        if b"__datetime__" in obj and obj[b"__datetime__"]:
-            return iso8601.parse_date(obj[b"s"], default_timezone=None)
-        if b"__uuid__" in obj and obj[b"__uuid__"]:
-            return UUID(obj[b"s"])
-        if b"__timedelta__" in obj and obj[b"__timedelta__"]:
-            return datetime.timedelta(**obj[b"s"])
-        if b"__arrow__" in obj and obj[b"__arrow__"]:
-            return arrow.get(obj[b"s"])
-
         # Fallthrough
         return obj
 
diff --git a/swh/core/api/tests/test_serializers.py b/swh/core/api/tests/test_serializers.py
--- a/swh/core/api/tests/test_serializers.py
+++ b/swh/core/api/tests/test_serializers.py
@@ -216,36 +216,6 @@
     assert decode_response(response) == DATA
 
 
-def test_serializers_decode_legacy_msgpack():
-    legacy_msgpack = {
-        "bytes": b"\xc4\x0e123456789\x99\xaf\xff\x00\x12",
-        "datetime_tz": (
-            b"\x82\xc4\x0c__datetime__\xc3\xc4\x01s\xd9 "
-            b"2015-03-04T18:25:13.001234+01:58"
-        ),
-        "datetime_utc": (
-            b"\x82\xc4\x0c__datetime__\xc3\xc4\x01s\xd9 "
-            b"2015-03-04T18:25:13.001234+00:00"
-        ),
-        "datetime_delta": (
-            b"\x82\xc4\r__timedelta__\xc3\xc4\x01s\x83\xa4"
-            b"days@\xa7seconds\x00\xacmicroseconds\x00"
-        ),
-        "arrow_date": (
-            b"\x82\xc4\t__arrow__\xc3\xc4\x01s\xd9 2018-04-25T16:17:53.533672+00:00"
-        ),
-        "swhtype": b"\xa4fake",
-        "swh_dict": b"\x82\xa7swhtype*\xa1d\xa4test",
-        "random_dict": b"\x81\xa7swhtype+",
-        "uuid": (
-            b"\x82\xc4\x08__uuid__\xc3\xc4\x01s\xd9$"
-            b"cdd8f804-9db6-40c3-93ab-5955d3836234"
-        ),
-    }
-    for k, v in legacy_msgpack.items():
-        assert msgpack_loads(v) == DATA[k]
-
-
 def test_serializers_encode_native_datetime():
     dt = datetime.datetime(2015, 1, 1, 12, 4, 42, 231455)
     with pytest.raises(ValueError, match="naive datetime"):
@@ -264,14 +234,6 @@
         == expected_dt
     )
 
-    # Legacy encoding
-    assert (
-        msgpack_loads(
-            b"\x82\xc4\x0c__datetime__\xc3\xc4\x01s\xba2015-01-01T12:04:42.231455"
-        )
-        == expected_dt
-    )
-
 
 def test_msgpack_extra_encoders_mutation():
     data = msgpack_dumps({}, extra_encoders=extra_encoders)