diff --git a/README.md b/README.md
index f15a222..1b16004 100644
--- a/README.md
+++ b/README.md
@@ -173,7 +173,7 @@ What this does:
 
 ## Public API
 
-- `init_assembly(gateway_url, api_key, agent_id=None, mode="auto", *, control_plane_url=None) -> AssemblyContext`
+- `init_assembly(gateway_url, api_key, agent_id=None, mode="auto", *, control_plane_url=None, allow_insecure=False) -> AssemblyContext`
 - Exceptions: `AssemblyError`, `AgentError`, `PolicyError`, `GatewayError`, `ConfigurationError`
 - Data models: `AgentConfig`, `AgentState`, `PolicyEvaluation`
 
@@ -206,6 +206,25 @@ Resolution order is **explicit kwarg > env-var > unset**:
 | `gateway_url` | `AA_GATEWAY_URL` |
 | `control_plane_url` | `AA_CONTROL_PLANE_URL` |
 
+### Insecure transport opt-in
+
+Agent registration dials the gateway's gRPC port over the native `register`
+call. By default a **plaintext `http://` register channel to a non-loopback
+host is refused** — the `Register` call carries the agent identity, so it must
+not travel unencrypted to a remote host. Loopback (local dev) and `https://`
+targets always pass.
+
+Pass `allow_insecure=True` to opt into plaintext to a non-loopback host, on a
+**trusted network only** (e.g. a private link where TLS terminates elsewhere).
+This mirrors the operator-control `connect(allow_insecure=...)` opt-in:
+
+```python
+init_assembly(
+    gateway_url="http://gateway.internal:7391",
+    allow_insecure=True,  # trusted-network only; leave False in production
+)
+```
+
 ## Error Handling
 
 ```python
diff --git a/agent_assembly/core/assembly.py b/agent_assembly/core/assembly.py
index f69fdda..b0d71e6 100644
--- a/agent_assembly/core/assembly.py
+++ b/agent_assembly/core/assembly.py
@@ -166,6 +166,7 @@ def init_assembly(
     spawned_by_tool: str | None = None,
     depth: int | None = None,
     enforcement_mode: EnforcementMode | None = None,
+    allow_insecure: bool = False,
 ) -> AssemblyContext:
     """Initialize the Agent Assembly SDK runtime for this process.
 
@@ -204,6 +205,15 @@ def init_assembly(
         the agent in dry-run / sandbox mode: every action proceeds (local checks
         fail open) and the gateway records would-be violations as shadow audit
         events.
+    :param allow_insecure: Opt into a plaintext (non-TLS) native ``register``
+        channel when the resolved gateway host is non-loopback (AAASM-4664).
+        Defaults to ``False`` — secure-by-default (AAASM-4655): a derived
+        plaintext ``http://`` register endpoint to a non-loopback host is
+        refused, since the ``Register`` call carries the agent identity and must
+        not travel unencrypted to a remote host. Set to ``True`` only on a
+        trusted network (loopback dev / private link), mirroring op-control's
+        ``connect(allow_insecure=...)`` semantics. Loopback and ``https://``
+        targets always pass regardless of this flag.
     """
     gateway_url = resolve_gateway_url(gateway_url)
     api_key = resolve_api_key(api_key)
@@ -267,7 +277,7 @@ def init_assembly(
                 runtime_client=runtime_client,
                 agent_id=resolved_agent_id,
                 enforcement_mode=enforcement_mode,
-                gateway_endpoint=resolve_gateway_grpc_endpoint(gateway_url),
+                gateway_endpoint=resolve_gateway_grpc_endpoint(gateway_url, allow_insecure=allow_insecure),
                 native_available=native_available,
                 team_id=team_id,
                 parent_agent_id=parent_agent_id,
diff --git a/test/unit/core/test_init_registration.py b/test/unit/core/test_init_registration.py
index 7525f4a..b33325f 100644
--- a/test/unit/core/test_init_registration.py
+++ b/test/unit/core/test_init_registration.py
@@ -513,6 +513,61 @@ def test_enforce_mode_propagates_register_failure(monkeypatch: pytest.MonkeyPatc
         )
 
 
+# A non-loopback gateway host reached over plaintext http:// — the register
+# endpoint TLS guard (AAASM-4655) fail-closes this by default, and the
+# allow_insecure opt-in (AAASM-4664) is what lets it through.
+_INSECURE_GW_URL = "http://gateway.test"
+_INSECURE_GRPC_ENDPOINT = "http://gateway.test:50051"
+
+
+def test_init_refuses_plaintext_nonloopback_register_by_default(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Omitting ``allow_insecure`` keeps init fail-closed: a plaintext http://
+    register channel to a non-loopback host is refused (AAASM-4664 preserves the
+    secure-by-default guard from AAASM-4655)."""
+    runtime_client = FakeRuntimeClient(decision="allow")
+    install_fake_core(monkeypatch, runtime_client)
+    _no_network(monkeypatch)
+    monkeypatch.setattr(core_assembly, "_register_adapters", lambda **_kwargs: [])
+
+    with pytest.raises(ConfigurationError, match="Failed to initialize assembly runtime"):
+        init_assembly(
+            gateway_url=_INSECURE_GW_URL,
+            api_key=_API_KEY,
+            agent_id="agent-insecure-default",
+            mode="sdk-only",
+        )
+    # The guard fires before register is dialed, so no registration happened.
+    assert runtime_client.register_calls == []
+
+
+def test_init_allow_insecure_permits_plaintext_nonloopback_register(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """``allow_insecure=True`` threads through to
+    ``resolve_gateway_grpc_endpoint`` and opts into a plaintext http:// register
+    channel to a non-loopback host (trusted-network only, AAASM-4664)."""
+    runtime_client = FakeRuntimeClient(decision="allow")
+    install_fake_core(monkeypatch, runtime_client)
+    _no_network(monkeypatch)
+    monkeypatch.setattr(core_assembly, "_register_adapters", lambda **_kwargs: [])
+
+    context = init_assembly(
+        gateway_url=_INSECURE_GW_URL,
+        api_key=_API_KEY,
+        agent_id="agent-insecure-optin",
+        mode="sdk-only",
+        allow_insecure=True,
+    )
+    try:
+        assert runtime_client.register_calls == [
+            ("agent-insecure-optin", "agent-insecure-optin", "python", _INSECURE_GRPC_ENDPOINT, None, None)
+        ]
+    finally:
+        context.shutdown()
+
+
 def _patched_register_adapters(adapter: _CapturingAdapter) -> object:
     """Build a stand-in for ``_register_adapters`` that drives the real
     interceptor builder and registers the capturing adapter with it."""