diff --git a/swh/model/model.py b/swh/model/model.py
--- a/swh/model/model.py
+++ b/swh/model/model.py
@@ -556,6 +556,25 @@
         )
 
 
+@attr.s(frozen=True, slots=True)
+class ExtID(BaseModel):
+    object_type: Final = "extid"
+
+    extid = attr.ib(type=bytes, validator=type_validator())
+    extid_type = attr.ib(type=str, validator=type_validator())
+    target = attr.ib(type=Sha1Git, validator=type_validator())
+    target_type = attr.ib(type=ObjectType, validator=type_validator())
+
+    @classmethod
+    def from_dict(cls, d):
+        return cls(
+            extid=d["extid"],
+            extid_type=d["extid_type"],
+            target=d["target"],
+            target_type=ObjectType(d["target_type"]),
+        )
+
+
 @attr.s(frozen=True, slots=True)
 class DirectoryEntry(BaseModel):
     object_type: Final = "directory_entry"