diff --git a/requirements.txt b/requirements.txt
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,9 +1,10 @@
 # Add here external Python modules dependencies, one per line. Module names
 # should match https://pypi.python.org/pypi names. For the full spec or
 # dependency lines, see https://pip.readthedocs.org/en/1.1/requirements.html
-vcversioner
 attrs
 attrs_strict
 hypothesis
-python-dateutil
 iso8601
+python-dateutil
+typing_extensions
+vcversioner
diff --git a/swh/model/model.py b/swh/model/model.py
--- a/swh/model/model.py
+++ b/swh/model/model.py
@@ -8,6 +8,7 @@
 from abc import ABCMeta, abstractmethod
 from enum import Enum
 from typing import Dict, List, Optional, Union
+from typing_extensions import Final
 
 import attr
 from attrs_strict import type_validator
@@ -90,6 +91,8 @@
 class Person(BaseModel):
     """Represents the author/committer of a revision or release."""
 
+    object_type: Final = "person"
+
     fullname = attr.ib(type=bytes, validator=type_validator())
     name = attr.ib(type=Optional[bytes], validator=type_validator())
     email = attr.ib(type=Optional[bytes], validator=type_validator())
@@ -134,6 +137,8 @@
 class Timestamp(BaseModel):
     """Represents a naive timestamp from a VCS."""
 
+    object_type: Final = "timestamp"
+
     seconds = attr.ib(type=int, validator=type_validator())
     microseconds = attr.ib(type=int, validator=type_validator())
 
@@ -154,6 +159,8 @@
 class TimestampWithTimezone(BaseModel):
     """Represents a TZ-aware timestamp from a VCS."""
 
+    object_type: Final = "timestamp_with_timezone"
+
     timestamp = attr.ib(type=Timestamp, validator=type_validator())
     offset = attr.ib(type=int, validator=type_validator())
     negative_utc = attr.ib(type=bool, validator=type_validator())
@@ -204,6 +211,8 @@
 class Origin(BaseModel):
     """Represents a software source: a VCS and an URL."""
 
+    object_type: Final = "origin"
+
     url = attr.ib(type=str, validator=type_validator())
 
 
@@ -212,6 +221,8 @@
     """Represents a visit of an origin at a given point in time, by a
     SWH loader."""
 
+    object_type: Final = "origin_visit"
+
     origin = attr.ib(type=str, validator=type_validator())
     date = attr.ib(type=datetime.datetime, validator=type_validator())
     status = attr.ib(
@@ -248,6 +259,8 @@
 
     """
 
+    object_type: Final = "origin_visit_status"
+
     origin = attr.ib(type=str, validator=type_validator())
     visit = attr.ib(type=int, validator=type_validator())
 
@@ -287,6 +300,8 @@
 class SnapshotBranch(BaseModel):
     """Represents one of the branches of a snapshot."""
 
+    object_type: Final = "snapshot_branch"
+
     target = attr.ib(type=bytes, validator=type_validator())
     target_type = attr.ib(type=TargetType, validator=type_validator())
 
@@ -307,6 +322,8 @@
 class Snapshot(BaseModel, HashableObject):
     """Represents the full state of an origin at a given point in time."""
 
+    object_type: Final = "snapshot"
+
     branches = attr.ib(
         type=Dict[bytes, Optional[SnapshotBranch]], validator=type_validator()
     )
@@ -330,6 +347,8 @@
 
 @attr.s(frozen=True)
 class Release(BaseModel, HashableObject):
+    object_type: Final = "release"
+
     name = attr.ib(type=bytes, validator=type_validator())
     message = attr.ib(type=Optional[bytes], validator=type_validator())
     target = attr.ib(type=Optional[Sha1Git], validator=type_validator())
@@ -380,6 +399,8 @@
 
 @attr.s(frozen=True)
 class Revision(BaseModel, HashableObject):
+    object_type: Final = "revision"
+
     message = attr.ib(type=bytes, validator=type_validator())
     author = attr.ib(type=Person, validator=type_validator())
     committer = attr.ib(type=Person, validator=type_validator())
@@ -425,6 +446,8 @@
 
 @attr.s(frozen=True)
 class DirectoryEntry(BaseModel):
+    object_type: Final = "directory_entry"
+
     name = attr.ib(type=bytes, validator=type_validator())
     type = attr.ib(type=str, validator=attr.validators.in_(["file", "dir", "rev"]))
     target = attr.ib(type=Sha1Git, validator=type_validator())
@@ -434,6 +457,8 @@
 
 @attr.s(frozen=True)
 class Directory(BaseModel, HashableObject):
+    object_type: Final = "directory"
+
     entries = attr.ib(type=List[DirectoryEntry], validator=type_validator())
     id = attr.ib(type=Sha1Git, validator=type_validator(), default=b"")
 
@@ -487,6 +512,8 @@
 
 @attr.s(frozen=True)
 class Content(BaseContent):
+    object_type: Final = "content"
+
     sha1 = attr.ib(type=bytes, validator=type_validator())
     sha1_git = attr.ib(type=Sha1Git, validator=type_validator())
     sha256 = attr.ib(type=bytes, validator=type_validator())
@@ -550,6 +577,8 @@
 
 @attr.s(frozen=True)
 class SkippedContent(BaseContent):
+    object_type: Final = "skipped_content"
+
     sha1 = attr.ib(type=Optional[bytes], validator=type_validator())
     sha1_git = attr.ib(type=Optional[Sha1Git], validator=type_validator())
     sha256 = attr.ib(type=Optional[bytes], validator=type_validator())
diff --git a/swh/model/tests/test_model.py b/swh/model/tests/test_model.py
--- a/swh/model/tests/test_model.py
+++ b/swh/model/tests/test_model.py
@@ -13,6 +13,7 @@
 import pytest
 
 from swh.model.model import (
+    BaseModel,
     Content,
     SkippedContent,
     Directory,
@@ -437,3 +438,23 @@
     snp_id = hash_to_bytes(snapshot_identifier(snp_dict))
     snp_model = Snapshot.from_dict(snp_dict)
     assert snp_model.id == snp_id
+
+
+@given(strategies.objects(split_content=True))
+def test_object_type(objtype_and_obj):
+    obj_type, obj = objtype_and_obj
+    assert obj_type == obj.object_type
+
+
+def test_object_type_is_final():
+    object_types = set()
+
+    def check_final(cls):
+        if not cls.__subclasses__():
+            assert cls.object_type not in object_types
+            object_types.add(cls.object_type)
+        else:
+            for subcls in cls.__subclasses__():
+                check_final(subcls)
+
+    check_final(BaseModel)