diff --git a/src/agentmsgs/core/types.py b/src/agentmsgs/core/types.py
new file mode 100644
index 0000000..563a839
--- /dev/null
+++ b/src/agentmsgs/core/types.py
@@ -0,0 +1,25 @@
+from __future__ import annotations
+import uuid
+import datetime
+from dataclasses import dataclass
+
+@dataclass(frozen=True, slots=True)
+class Agent:
+    id: uuid.UUID
+    name: str
+    def __hash__(self): return hash(self.id)
+    def __eq__(self, other): return isinstance(other, Agent) and self.id == other.id
+
+@dataclass(frozen=True, slots=True)
+class Message:
+    id: uuid.UUID
+    sender: Agent
+    content: str
+    seq: int
+    ts: datetime.datetime
+
+@dataclass(frozen=True, slots=True)
+class Thread:
+    id: uuid.UUID
+    participants: frozenset[Agent]
+    created_at: datetime.datetime
diff --git a/tests/test_types.py b/tests/test_types.py
new file mode 100644
index 0000000..90fbe4b
--- /dev/null
+++ b/tests/test_types.py
@@ -0,0 +1,24 @@
+import uuid
+from agentmsgs.core.types import Agent, Thread, Message
+import datetime
+
+def test_agent_identity_on_id_not_name():
+    a1 = Agent(id=uuid.uuid4(), name="Alice")
+    a2 = Agent(id=uuid.uuid4(), name="Alice")
+    assert a1 != a2  # different id => not equal even though name same
+    assert hash(a1) != hash(a2)
+
+def test_agent_hash_on_id():
+    uid = uuid.uuid4()
+    a1 = Agent(id=uid, name="Alice")
+    a2 = Agent(id=uid, name="Bob")  # same id, different name => equal per design (id is identity)
+    assert a1 == a2
+    assert hash(a1) == hash(a2)
+
+def test_thread_multiple_with_same_participants_allowed():
+    a = Agent(id=uuid.uuid4(), name="A")
+    b = Agent(id=uuid.uuid4(), name="B")
+    t1 = Thread(id=uuid.uuid4(), participants=frozenset({a,b}), created_at=datetime.datetime.now(datetime.timezone.utc))
+    t2 = Thread(id=uuid.uuid4(), participants=frozenset({a,b}), created_at=datetime.datetime.now(datetime.timezone.utc))
+    assert t1 != t2
+    assert t1.participants == t2.participants