diff --git a/README.md b/README.md
index fe2b68d..8b55b19 100644
--- a/README.md
+++ b/README.md
@@ -243,6 +243,50 @@ client.voice_in_trunks().update(created)
 client.voice_in_trunks().delete(created.id)
 ```
 
+#### SIP Registration (2026-04-16)
+
+A Voice In Trunk can also authenticate inbound calls via SIP registration
+credentials generated by DIDWW. The SDK auto-cascades the dependent fields
+the server requires:
+
+* setting `enabled_sip_registration = True` clears any previously-set
+  `host` / `port` (the server rejects them with 422 otherwise);
+* setting `host` to a non-`None` value flips `enabled_sip_registration`
+  back to `False` and forces `use_did_in_ruri = False` so the server
+  accepts the disable PATCH.
+
+The server generates `incoming_auth_username` and `incoming_auth_password`
+and surfaces them in the response when SIP registration is enabled.
+
+```python
+sip = SipConfiguration()
+sip.enabled_sip_registration = True
+sip.use_did_in_ruri = True
+sip.cnam_lookup = True
+
+trunk = VoiceInTrunk()
+trunk.name = "Office (registered)"
+trunk.configuration = sip
+created = client.voice_in_trunks().create(trunk).data
+
+# created.configuration.incoming_auth_username — server-generated
+# created.configuration.incoming_auth_password — server-generated
+```
+
+To disable SIP registration on an existing trunk, just set `host` — the
+cascade flips `enabled_sip_registration` to `False` and `use_did_in_ruri`
+to `False` automatically:
+
+```python
+disable = SipConfiguration()
+disable.host = "sip.example.com"
+
+trunk = VoiceInTrunk()
+trunk.id = "trunk-uuid"
+trunk.configuration = disable
+client.voice_in_trunks().update(trunk)
+```
+
 ### Voice In Trunk Groups
 
 ```python
diff --git a/examples/README.md b/examples/README.md
index 08b072a..86ae736 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -34,6 +34,7 @@ DIDWW_API_KEY=your_api_key python examples/balance.py
 | [`trunks.py`](trunks.py) | Creates SIP and PSTN trunks, prints details, then deletes them. |
 | [`regions.py`](regions.py) | Lists regions, filters by country, and fetches a specific region. |
 | [`voice_in_trunks.py`](voice_in_trunks.py) | Lists voice in trunks with their configurations and POP details. |
+| [`voice_in_trunk_sip_registration.py`](voice_in_trunk_sip_registration.py) | End-to-end SIP registration flow: create with `enabled_sip_registration=True`, rename, disable by setting `host`, re-enable by toggling the flag. The SDK keeps the dependent fields (`host`, `port`, `use_did_in_ruri`) aligned with the server's validation rules automatically. |
 | [`orders.py`](orders.py) | Lists orders, creates a DID order, and cancels it. |
 | [`orders_available_dids.py`](orders_available_dids.py) | Orders a specific available DID using included DID group SKU. |
 | [`orders_reservation_dids.py`](orders_reservation_dids.py) | Reserves a DID and then places an order from that reservation. |
diff --git a/examples/voice_in_trunk_sip_registration.py b/examples/voice_in_trunk_sip_registration.py
new file mode 100644
index 0000000..74cf93d
--- /dev/null
+++ b/examples/voice_in_trunk_sip_registration.py
@@ -0,0 +1,81 @@
+"""End-to-end SIP registration flow on /voice_in_trunks (API 2026-04-16):
+create with sip_registration enabled → rename → disable by setting `host`
+→ re-enable by toggling the flag. Demonstrates how the SDK keeps the
+dependent fields (`host`, `port`, `use_did_in_ruri`) aligned with the
+server's validation rules. The sandbox trunk is left in place after the
+script completes.
+
+Usage: DIDWW_API_KEY=xxx python examples/voice_in_trunk_sip_registration.py
+"""
+import time
+from client_factory import create_client
+from didww.resources.configuration.sip import SipConfiguration
+from didww.resources.voice_in_trunk import VoiceInTrunk
+from didww.enums import CliFormat, Codec, TransportProtocol
+
+client = create_client()
+
+print("=== Python SDK — SIP registration flow ===")
+
+# 1) Create with sip_registration enabled.
+print("\n[1/4] Create with sip_registration enabled...")
+sip = SipConfiguration()
+sip.enabled_sip_registration = True
+sip.use_did_in_ruri = True
+sip.cnam_lookup = False
+sip.codec_ids = [Codec.PCMU, Codec.PCMA]
+sip.transport_protocol_id = TransportProtocol.UDP
+
+trunk = VoiceInTrunk()
+trunk.name = f"py-sip-registration-{int(time.time())}"
+trunk.priority = 1
+trunk.weight = 100
+trunk.cli_format = CliFormat.E164
+trunk.ringing_timeout = 30
+trunk.configuration = sip
+
+created = client.voice_in_trunks().create(trunk).data
+trunk_id = created.id
+print(f"  id={trunk_id}")
+print(f"  incoming_auth_username={created.configuration.incoming_auth_username!r}")
+print(f"  incoming_auth_password={created.configuration.incoming_auth_password!r}")
+
+# 2) Rename — single-field PATCH.
+print("\n[2/4] Rename trunk...")
+created.name = f"py-renamed-{int(time.time())}"
+client.voice_in_trunks().update(created)
+print(f"  name={created.name}")
+
+# 3) Disable sip_registration by setting `host`.
+print("\n[3/4] Disable by setting host...")
+disable = SipConfiguration()
+disable.host = "203.0.113.10"
+update = VoiceInTrunk()
+update.id = trunk_id
+update.configuration = disable
+client.voice_in_trunks().update(update)
+fresh = client.voice_in_trunks().find(trunk_id).data
+print(f"  enabled_sip_registration={fresh.configuration.enabled_sip_registration!r}")
+print(f"  use_did_in_ruri={fresh.configuration.use_did_in_ruri!r}")
+print(f"  host={fresh.configuration.host!r}")
+print(f"  incoming_auth_username={fresh.configuration.incoming_auth_username!r}")
+
+# 4) Re-enable sip_registration. The SDK should send host=None / port=None on
+#    the wire so the server clears the values it had persisted.
+print("\n[4/4] Re-enable by toggling enabled_sip_registration...")
+re_enable = SipConfiguration()
+re_enable.enabled_sip_registration = True
+re_enable.use_did_in_ruri = True
+update = VoiceInTrunk()
+update.id = trunk_id
+update.configuration = re_enable
+try:
+    client.voice_in_trunks().update(update)
+    fresh = client.voice_in_trunks().find(trunk_id).data
+    print(f"  enabled_sip_registration={fresh.configuration.enabled_sip_registration!r}")
+    print(f"  host={fresh.configuration.host!r}")
+    print(f"  incoming_auth_username={fresh.configuration.incoming_auth_username!r}")
+    print(f"\n=== PASS — trunk {trunk_id} left in sandbox ===")
+except Exception as e:
+    print(f"  ✗ FAIL: {e}")
+    print(f"\n=== FAIL at re-enable — trunk {trunk_id} left in sandbox ===")
diff --git a/pyproject.toml b/pyproject.toml
index 5703f87..4d06c2f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "didww"
-version = "3.0.0"
+version = "3.1.0"
 description = "Python SDK for DIDWW API v3"
 readme = "README.md"
 requires-python = ">=3.9"
diff --git a/src/didww/enums.py b/src/didww/enums.py
index 7640ae6..236f551 100644
--- a/src/didww/enums.py
+++ b/src/didww/enums.py
@@ -132,6 +132,21 @@ class DiversionRelayPolicy(str, Enum):
     TEL = "tel"
 
 
+class DiversionInjectMode(str, Enum):
+    """Diversion header injection mode for SIP INVITE. (API 2026-04-16)"""
+    NONE = "none"
+    DID_NUMBER = "did_number"
+
+
+class NetworkProtocolPriority(str, Enum):
+    """SIP network protocol priority. (API 2026-04-16)"""
+    FORCE_IPV4 = "force_ipv4"
+    FORCE_IPV6 = "force_ipv6"
+    ANY = "any"
+    PREFER_IPV4 = "prefer_ipv4"
+    PREFER_IPV6 = "prefer_ipv6"
+
+
 class StirShakenMode(str, Enum):
     DISABLED = "disabled"
     ORIGINAL = "original"
diff --git a/src/didww/mixins.py b/src/didww/mixins.py
new file mode 100644
index 0000000..17a0313
--- /dev/null
+++ b/src/didww/mixins.py
@@ -0,0 +1,25 @@
+"""Reusable mixins shared across resource hierarchies."""
+
+
+class RedactsSensitiveAttributes:
+    """Provides a `__repr__` that masks values of attribute keys listed in
+    ``_sensitive_attrs`` so credentials never leak through default
+    ``print()`` / logging / unhandled exception output.
+
+    The wire payload is unaffected — the host class's serializer (e.g.
+    ``to_jsonapi``) still emits the real values.
+
+    Used by ``TrunkConfiguration`` and ``AuthenticationMethod``, which
+    both expose an ``_attributes`` dict and a ``_sensitive_attrs``
+    frozenset that subclasses extend.
+    """
+
+    _sensitive_attrs = frozenset()
+
+    def __repr__(self):
+        parts = []
+        for key, value in self._attributes.items():
+            if key in self._sensitive_attrs and value is not None:
+                value = "[FILTERED]"
+            parts.append(f"{key}={value!r}")
+        return f"{self.__class__.__name__}({', '.join(parts)})"
diff --git a/src/didww/resources/authentication_method.py b/src/didww/resources/authentication_method.py
index e15fb8a..2af571d 100644
--- a/src/didww/resources/authentication_method.py
+++ b/src/didww/resources/authentication_method.py
@@ -1,7 +1,13 @@
-class AuthenticationMethod:
+from didww.mixins import RedactsSensitiveAttributes
+
+
+class AuthenticationMethod(RedactsSensitiveAttributes):
     """Base class for polymorphic VoiceOutTrunk authentication methods."""
     _type = None
     _type_map = {}
+    # Subclasses extend `_sensitive_attrs` (inherited from
+    # RedactsSensitiveAttributes) to mark credential-bearing keys; the
+    # mixin's `__repr__` masks their values with `[FILTERED]`.
 
     def __init__(self, **kwargs):
         self._attributes = kwargs
@@ -61,6 +67,7 @@ class IpOnlyAuthenticationMethod(AuthenticationMethod):
 
 class CredentialsAndIpAuthenticationMethod(AuthenticationMethod):
     _type = "credentials_and_ip"
+    _sensitive_attrs = frozenset({"username", "password"})
 
     allowed_sip_ips = _plain("allowed_sip_ips")
     tech_prefix = _plain("tech_prefix")
diff --git a/src/didww/resources/configuration/base.py b/src/didww/resources/configuration/base.py
index 15e5ef8..1b322d3 100644
--- a/src/didww/resources/configuration/base.py
+++ b/src/didww/resources/configuration/base.py
@@ -1,6 +1,17 @@
-class TrunkConfiguration:
+from didww.mixins import RedactsSensitiveAttributes
+
+
+class TrunkConfiguration(RedactsSensitiveAttributes):
     _type = None
     _type_map = {}
+    # Set of attribute keys that are deserialized from server responses
+    # but MUST NOT be sent in POST/PATCH request bodies. Subclasses should
+    # extend this set to mark server-generated read-only fields. The server
+    # rejects writes to these keys with 400 Param not allowed.
+    _read_only_attrs = frozenset()
+    # Subclasses extend `_sensitive_attrs` (inherited from
+    # RedactsSensitiveAttributes) to mark credential-bearing keys; the
+    # mixin's `__repr__` masks their values with `[FILTERED]`.
 
     def __init__(self, attributes=None):
         self._attributes = attributes or {}
@@ -12,9 +23,14 @@ def _set_attr(self, key, value):
         self._attributes[key] = value
 
     def to_jsonapi(self):
+        attrs = {
+            k: v
+            for k, v in self._attributes.items()
+            if k not in self._read_only_attrs
+        }
         return {
             "type": self._type,
-            "attributes": dict(self._attributes),
+            "attributes": attrs,
         }
 
     @classmethod
diff --git a/src/didww/resources/configuration/sip.py b/src/didww/resources/configuration/sip.py
index 9e6dd13..af9d0b5 100644
--- a/src/didww/resources/configuration/sip.py
+++ b/src/didww/resources/configuration/sip.py
@@ -1,8 +1,10 @@
 from didww.resources.configuration.base import TrunkConfiguration
 from didww.enums import (
     Codec,
+    DiversionInjectMode,
     DiversionRelayPolicy,
     MediaEncryptionMode,
+    NetworkProtocolPriority,
     ReroutingDisconnectCode,
     RxDtmfFormat,
     SstRefreshMethod,
@@ -36,14 +38,41 @@ def _enum_list(key, cls):
 
 class SipConfiguration(TrunkConfiguration):
     _type = "sip_configurations"
+    # Server-generated SIP registration credentials. The API rejects any
+    # write attempt with 400 Param not allowed, so they are deserialized
+    # from responses (readable via the property) but stripped from
+    # POST/PATCH request bodies. (API 2026-04-16)
+    _read_only_attrs = frozenset({
+        "incoming_auth_username",
+        "incoming_auth_password",
+    })
+    _sensitive_attrs = frozenset({
+        "auth_password",
+        "incoming_auth_username",
+        "incoming_auth_password",
+    })
 
     username               = _plain("username")
-    host                   = _plain("host")
     port                   = _plain("port")
     auth_enabled           = _plain("auth_enabled")
     resolve_ruri           = _plain("resolve_ruri")
     auth_user              = _plain("auth_user")
     auth_password          = _plain("auth_password")
+
+    # `host` cascades dependent fields whose constraints are server-enforced
+    # (API 2026-04-16): setting host to a non-null value implies
+    # enabled_sip_registration = False and use_did_in_ruri = False.
+    @property
+    def host(self):
+        return self._attr("host")
+
+    @host.setter
+    def host(self, value):
+        if value is not None:
+            self._set_attr("enabled_sip_registration", False)
+            self._set_attr("use_did_in_ruri", False)
+        self._set_attr("host", value)
+
     auth_from_user         = _plain("auth_from_user")
     auth_from_domain       = _plain("auth_from_domain")
     sst_enabled            = _plain("sst_enabled")
@@ -59,16 +88,57 @@ class SipConfiguration(TrunkConfiguration):
     max_30x_redirects      = _plain("max_30x_redirects")
     allowed_rtp_ips        = _plain("allowed_rtp_ips")
 
+    # API 2026-04-16 SIP registration + protocol attributes.
+    #
+    # Server-side validation rules for `enabled_sip_registration`:
+    #   * When True, the trunk's `host` and `port` must be left blank
+    #     (server returns 422 otherwise).
+    #   * When disabling sip registration on an existing trunk, the same
+    #     PATCH must also set `host` to a non-blank value and
+    #     `use_did_in_ruri` to False, or the server returns 422.
+    use_did_in_ruri          = _plain("use_did_in_ruri")
+    cnam_lookup              = _plain("cnam_lookup")
+
+    # `enabled_sip_registration` cascades dependent fields whose constraints
+    # are server-enforced (API 2026-04-16):
+    #   * True  -> host = None, port = None (always — a PATCH against an
+    #              existing trunk that has host/port persisted on the
+    #              server side MUST explicitly nullify them or the server
+    #              rejects with 422).
+    #   * False -> use_did_in_ruri = False (server requires it disabled
+    #              whenever sip_registration is disabled).
+    @property
+    def enabled_sip_registration(self):
+        return self._attr("enabled_sip_registration")
+
+    @enabled_sip_registration.setter
+    def enabled_sip_registration(self, value):
+        if value is True:
+            self._set_attr("host", None)
+            self._set_attr("port", None)
+        elif value is False:
+            self._set_attr("use_did_in_ruri", False)
+        self._set_attr("enabled_sip_registration", value)
+
+
+    # Read-only: server-generated when SIP registration is enabled.
+    # Deserialized from responses but stripped on serialize via
+    # `_read_only_attrs` above (API rejects writes with 400 Param not allowed).
+    incoming_auth_username = property(lambda self: self._attr("incoming_auth_username"))
+    incoming_auth_password = property(lambda self: self._attr("incoming_auth_password"))
+
     codec_ids                     = _enum_list("codec_ids", Codec)
     rerouting_disconnect_code_ids = _enum_list("rerouting_disconnect_code_ids", ReroutingDisconnectCode)
 
-    transport_protocol_id = _enum("transport_protocol_id", TransportProtocol)
-    rx_dtmf_format_id     = _enum("rx_dtmf_format_id", RxDtmfFormat)
-    tx_dtmf_format_id     = _enum("tx_dtmf_format_id", TxDtmfFormat)
-    sst_refresh_method_id = _enum("sst_refresh_method_id", SstRefreshMethod)
-    media_encryption_mode = _enum("media_encryption_mode", MediaEncryptionMode)
-    stir_shaken_mode      = _enum("stir_shaken_mode", StirShakenMode)
-    diversion_relay_policy = _enum("diversion_relay_policy", DiversionRelayPolicy)
+    transport_protocol_id      = _enum("transport_protocol_id", TransportProtocol)
+    rx_dtmf_format_id          = _enum("rx_dtmf_format_id", RxDtmfFormat)
+    tx_dtmf_format_id          = _enum("tx_dtmf_format_id", TxDtmfFormat)
+    sst_refresh_method_id      = _enum("sst_refresh_method_id", SstRefreshMethod)
+    media_encryption_mode      = _enum("media_encryption_mode", MediaEncryptionMode)
+    stir_shaken_mode           = _enum("stir_shaken_mode", StirShakenMode)
+    diversion_relay_policy     = _enum("diversion_relay_policy", DiversionRelayPolicy)
+    diversion_inject_mode      = _enum("diversion_inject_mode", DiversionInjectMode)
+    network_protocol_priority  = _enum("network_protocol_priority", NetworkProtocolPriority)
 
 
 TrunkConfiguration.register("sip_configurations", SipConfiguration)
diff --git a/tests/fixtures/voice_in_trunks/create_sip_with_rerouting.yaml b/tests/fixtures/voice_in_trunks/create_sip_with_rerouting.yaml
index 4fe9b07..2a11ac2 100644
--- a/tests/fixtures/voice_in_trunks/create_sip_with_rerouting.yaml
+++ b/tests/fixtures/voice_in_trunks/create_sip_with_rerouting.yaml
@@ -1,7 +1,6 @@
 interactions:
 - request:
-    body: '{"data":{"type":"voice_in_trunks","attributes":{"configuration":{"type":"sip_configurations","attributes":{"username":"username","host":"203.0.113.110","sst_refresh_method_id":1,"port":5060,"codec_ids":[9,10,8,7,6],"rerouting_disconnect_code_ids":[56,58,59,60,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,86,87,88,89,90,91,92,96,97,98,99,101,102,103,104,105,106,107,108,1505],"media_encryption_mode":"zrtp","stir_shaken_mode":"pai","allowed_rtp_ips":["203.0.113.1"]}},"name":"hello,
-      test sip trunk"}}}'
+    body: '{"data":{"type":"voice_in_trunks","attributes":{"configuration":{"type":"sip_configurations","attributes":{"username":"username","enabled_sip_registration":false,"use_did_in_ruri":false,"host":"203.0.113.110","sst_refresh_method_id":1,"port":5060,"codec_ids":[9,10,8,7,6],"rerouting_disconnect_code_ids":[56,58,59,60,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,86,87,88,89,90,91,92,96,97,98,99,101,102,103,104,105,106,107,108,1505],"media_encryption_mode":"zrtp","stir_shaken_mode":"pai","allowed_rtp_ips":["203.0.113.1"],"diversion_relay_policy":"as_is","diversion_inject_mode":"did_number","network_protocol_priority":"force_ipv4","cnam_lookup":true}},"name":"hello, test sip trunk"}}}'
     headers:
       Accept:
       - application/vnd.api+json
@@ -13,49 +12,7 @@ interactions:
     uri: https://sandbox-api.didww.com/v3/voice_in_trunks
   response:
     body:
-      string: "{\n  \"data\": {\n    \"id\": \"a80006b6-4183-4865-8b99-7ebbd359a762\"\
-        ,\n    \"type\": \"voice_in_trunks\",\n    \"attributes\": {\n      \"priority\"\
-        : 1,\n      \"capacity_limit\": null,\n      \"weight\": 65535,\n      \"\
-        name\": \"hello, test sip trunk\",\n      \"cli_format\": \"e164\",\n    \
-        \  \"cli_prefix\": null,\n      \"description\": null,\n      \"ringing_timeout\"\
-        : null,\n      \"configuration\": {\n        \"type\": \"sip_configurations\"\
-        ,\n        \"attributes\": {\n          \"username\": \"username\",\n    \
-        \      \"host\": \"203.0.113.110\",\n          \"port\": 5060,\n        \
-        \  \"codec_ids\": [\n            9,\n            10,\n            8,\n   \
-        \         7,\n            6\n          ],\n          \"rx_dtmf_format_id\"\
-        : 1,\n          \"tx_dtmf_format_id\": 1,\n          \"resolve_ruri\": false,\n\
-        \          \"auth_enabled\": false,\n          \"auth_user\": null,\n    \
-        \      \"auth_password\": null,\n          \"auth_from_user\": null,\n   \
-        \       \"auth_from_domain\": null,\n          \"sst_enabled\": false,\n \
-        \         \"sst_min_timer\": 600,\n          \"sst_max_timer\": 900,\n   \
-        \       \"sst_accept_501\": true,\n          \"sip_timer_b\": 8000,\n    \
-        \      \"dns_srv_failover_timer\": 2000,\n          \"rtp_ping\": false,\n\
-        \          \"rtp_timeout\": 30,\n          \"force_symmetric_rtp\": false,\n\
-        \          \"symmetric_rtp_ignore_rtcp\": false,\n          \"rerouting_disconnect_code_ids\"\
-        : [\n            56,\n            58,\n            59,\n            60,\n\
-        \            64,\n            65,\n            66,\n            67,\n    \
-        \        68,\n            69,\n            70,\n            71,\n        \
-        \    72,\n            73,\n            74,\n            75,\n            76,\n\
-        \            77,\n            78,\n            79,\n            80,\n    \
-        \        81,\n            82,\n            83,\n            84,\n        \
-        \    86,\n            87,\n            88,\n            89,\n            90,\n\
-        \            91,\n            92,\n            96,\n            97,\n    \
-        \        98,\n            99,\n            101,\n            102,\n      \
-        \      103,\n            104,\n            105,\n            106,\n      \
-        \      107,\n            108,\n            1505\n          ],\n          \"\
-        sst_session_expires\": null,\n          \"sst_refresh_method_id\": 1,\n  \
-        \        \"transport_protocol_id\": 1,\n          \"max_transfers\": 0,\n\
-        \          \"max_30x_redirects\": 0,\n          \"media_encryption_mode\"\
-        : \"zrtp\",\n          \"stir_shaken_mode\": \"pai\",\n          \"allowed_rtp_ips\"\
-        : [\n            \"203.0.113.1\"\n          ]\n        }\n      },\n      \"\
-        created_at\": \"2018-12-28T17:37:48.010Z\"\n    },\n    \"relationships\"\
-        : {\n      \"voice_in_trunk_group\": {\n        \"links\": {\n          \"\
-        self\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/relationships/voice_in_trunk_group\"\
-        ,\n          \"related\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/voice_in_trunk_group\"\
-        \n        }\n      },\n      \"pop\": {\n        \"links\": {\n          \"\
-        self\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/relationships/pop\"\
-        ,\n          \"related\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/pop\"\
-        \n        }\n      }\n    }\n  }\n}"
+      string: '{"data":{"id":"a80006b6-4183-4865-8b99-7ebbd359a762","type":"voice_in_trunks","attributes":{"priority":1,"capacity_limit":null,"weight":65535,"name":"hello, test sip trunk","cli_format":"e164","cli_prefix":null,"description":null,"ringing_timeout":null,"configuration":{"type":"sip_configurations","attributes":{"username":"username","enabled_sip_registration":false,"use_did_in_ruri":false,"host":"203.0.113.110","port":5060,"codec_ids":[9,10,8,7,6],"rx_dtmf_format_id":1,"tx_dtmf_format_id":1,"resolve_ruri":false,"auth_enabled":false,"auth_user":null,"auth_password":null,"auth_from_user":null,"auth_from_domain":null,"sst_enabled":false,"sst_min_timer":600,"sst_max_timer":900,"sst_accept_501":true,"sip_timer_b":8000,"dns_srv_failover_timer":2000,"rtp_ping":false,"rtp_timeout":30,"force_symmetric_rtp":false,"symmetric_rtp_ignore_rtcp":false,"rerouting_disconnect_code_ids":[56,58,59,60,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,86,87,88,89,90,91,92,96,97,98,99,101,102,103,104,105,106,107,108,1505],"sst_session_expires":null,"sst_refresh_method_id":1,"transport_protocol_id":1,"max_transfers":0,"max_30x_redirects":0,"media_encryption_mode":"zrtp","stir_shaken_mode":"pai","allowed_rtp_ips":["203.0.113.1"],"network_protocol_priority":"force_ipv4","enabled_sip_registration":false,"use_did_in_ruri":false,"diversion_relay_policy":"as_is","diversion_inject_mode":"did_number","cnam_lookup":true,"incoming_auth_username":null,"incoming_auth_password":null}},"created_at":"2018-12-28T17:37:48.010Z"},"relationships":{"voice_in_trunk_group":{"links":{"self":"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/relationships/voice_in_trunk_group","related":"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/voice_in_trunk_group"}},"pop":{"links":{"self":"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/relationships/pop","related":"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/pop"}}}}}'
     headers:
       Content-Type:
       - application/vnd.api+json
diff --git a/tests/fixtures/voice_in_trunks/create_with_sip_registration.yaml b/tests/fixtures/voice_in_trunks/create_with_sip_registration.yaml
new file mode 100644
index 0000000..5a3c813
--- /dev/null
+++ b/tests/fixtures/voice_in_trunks/create_with_sip_registration.yaml
@@ -0,0 +1,24 @@
+interactions:
+- request:
+    body: '{"data":{"type":"voice_in_trunks","attributes":{"configuration":{"type":"sip_configurations","attributes":{"host":null,"port":null,"enabled_sip_registration":true,"use_did_in_ruri":true,"cnam_lookup":true,"diversion_relay_policy":"as_is","diversion_inject_mode":"did_number","network_protocol_priority":"prefer_ipv4"}},"name":"sip-registration","priority":1,"weight":100,"cli_format":"e164","ringing_timeout":30}}}'
+    headers:
+      Accept:
+      - application/vnd.api+json
+      Api-Key:
+      - test-api-key
+      Content-Type:
+      - application/vnd.api+json
+      X-DIDWW-API-Version:
+      - '2026-04-16'
+    method: POST
+    uri: https://sandbox-api.didww.com/v3/voice_in_trunks
+  response:
+    body:
+      string: '{"data":{"id":"f1c5d834-1d1f-49cc-8e88-3f73c0a35b31","type":"voice_in_trunks","attributes":{"name":"sip-registration","priority":1,"weight":100,"cli_format":"e164","ringing_timeout":30,"configuration":{"type":"sip_configurations","attributes":{"username":null,"host":null,"port":null,"enabled_sip_registration":true,"use_did_in_ruri":true,"cnam_lookup":true,"diversion_relay_policy":"as_is","diversion_inject_mode":"did_number","network_protocol_priority":"prefer_ipv4","incoming_auth_username":"7e3IUOSKtroNLfM6","incoming_auth_password":"31kSndbuugzPEu8M"}}}}}'
+    headers:
+      Content-Type:
+      - application/vnd.api+json
+    status:
+      code: 201
+      message: Created
+version: 1
diff --git a/tests/fixtures/voice_in_trunks/disable_sip_registration.yaml b/tests/fixtures/voice_in_trunks/disable_sip_registration.yaml
new file mode 100644
index 0000000..400a8e2
--- /dev/null
+++ b/tests/fixtures/voice_in_trunks/disable_sip_registration.yaml
@@ -0,0 +1,24 @@
+interactions:
+- request:
+    body: '{"data":{"type":"voice_in_trunks","id":"57a939dd-1600-41a6-80b1-f624e22a1f4c","attributes":{"configuration":{"type":"sip_configurations","attributes":{"enabled_sip_registration":false,"use_did_in_ruri":false,"host":"203.0.113.10"}}}}}'
+    headers:
+      Accept:
+      - application/vnd.api+json
+      Api-Key:
+      - test-api-key
+      Content-Type:
+      - application/vnd.api+json
+      X-DIDWW-API-Version:
+      - '2026-04-16'
+    method: PATCH
+    uri: https://sandbox-api.didww.com/v3/voice_in_trunks/57a939dd-1600-41a6-80b1-f624e22a1f4c
+  response:
+    body:
+      string: '{"data":{"id":"57a939dd-1600-41a6-80b1-f624e22a1f4c","type":"voice_in_trunks","attributes":{"name":"Office","priority":1,"weight":65535,"cli_format":"e164","configuration":{"type":"sip_configurations","attributes":{"username":null,"host":"203.0.113.10","port":null,"enabled_sip_registration":false,"use_did_in_ruri":false,"cnam_lookup":true,"diversion_relay_policy":"none","diversion_inject_mode":"did_number","network_protocol_priority":"prefer_ipv4","incoming_auth_username":null,"incoming_auth_password":null}}}}}'
+    headers:
+      Content-Type:
+      - application/vnd.api+json
+    status:
+      code: 200
+      message: OK
+version: 1
diff --git a/tests/fixtures/voice_in_trunks/list.yaml b/tests/fixtures/voice_in_trunks/list.yaml
index 556f8ac..3f056aa 100644
--- a/tests/fixtures/voice_in_trunks/list.yaml
+++ b/tests/fixtures/voice_in_trunks/list.yaml
@@ -12,70 +12,7 @@ interactions:
     uri: https://sandbox-api.didww.com/v3/voice_in_trunks
   response:
     body:
-      string: "{\n  \"data\": [\n    {\n      \"id\": \"2b4b1fcf-fe6a-4de9-8a58-7df46820ba13\"\
-        ,\n      \"type\": \"voice_in_trunks\",\n      \"attributes\": {\n       \
-        \ \"priority\": 1,\n        \"capacity_limit\": null,\n        \"weight\"\
-        : 65535,\n        \"name\": \"sample trunk pstn\",\n        \"cli_format\"\
-        : \"e164\",\n        \"cli_prefix\": \"\",\n        \"description\": \"\"\
-        ,\n        \"ringing_timeout\": null,\n        \"configuration\": {\n    \
-        \      \"type\": \"pstn_configurations\",\n          \"attributes\": {\n \
-        \           \"dst\": \"442080995011\"\n          }\n        },\n        \"\
-        created_at\": \"2018-12-28T15:03:48.751Z\"\n      },\n      \"relationships\"\
-        : {\n        \"voice_in_trunk_group\": {\n          \"links\": {\n       \
-        \     \"self\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/2b4b1fcf-fe6a-4de9-8a58-7df46820ba13/relationships/voice_in_trunk_group\"\
-        ,\n            \"related\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/2b4b1fcf-fe6a-4de9-8a58-7df46820ba13/voice_in_trunk_group\"\
-        \n          },\n          \"data\": null\n        },\n        \"pop\": {\n\
-        \          \"links\": {\n            \"self\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/2b4b1fcf-fe6a-4de9-8a58-7df46820ba13/relationships/pop\"\
-        ,\n            \"related\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/2b4b1fcf-fe6a-4de9-8a58-7df46820ba13/pop\"\
-        \n          },\n          \"data\": null\n        }\n      }\n    },\n   \
-        \ {\n      \"id\": \"24cec518-da51-4274-9a4b-1aad910b996f\",\n      \"type\"\
-        : \"voice_in_trunks\",\n      \"attributes\": {\n        \"priority\": 1,\n\
-        \        \"capacity_limit\": null,\n        \"weight\": 65535,\n        \"\
-        name\": \"Sip trunk sample\",\n        \"cli_format\": \"local\",\n      \
-        \  \"cli_prefix\": \"\",\n        \"description\": \"\",\n        \"ringing_timeout\"\
-        : null,\n        \"configuration\": {\n          \"type\": \"sip_configurations\"\
-        ,\n          \"attributes\": {\n            \"username\": \"username\",\n\
-        \            \"host\": \"203.0.113.78\",\n            \"port\": 8060,\n \
-        \           \"codec_ids\": [\n              9,\n              10,\n      \
-        \        8\n            ],\n            \"rx_dtmf_format_id\": 1,\n      \
-        \      \"tx_dtmf_format_id\": 1,\n            \"resolve_ruri\": true,\n  \
-        \          \"auth_enabled\": true,\n            \"auth_user\": \"auth_user\"\
-        ,\n            \"auth_password\": \"auth_password\",\n            \"auth_from_user\"\
-        : \"\",\n            \"auth_from_domain\": \"\",\n            \"sst_enabled\"\
-        : false,\n            \"sst_min_timer\": 600,\n            \"sst_max_timer\"\
-        : 900,\n            \"sst_accept_501\": true,\n            \"sip_timer_b\"\
-        : 8000,\n            \"dns_srv_failover_timer\": 2000,\n            \"rtp_ping\"\
-        : false,\n            \"rtp_timeout\": 30,\n            \"force_symmetric_rtp\"\
-        : false,\n            \"symmetric_rtp_ignore_rtcp\": false,\n            \"\
-        rerouting_disconnect_code_ids\": null,\n            \"sst_session_expires\"\
-        : null,\n            \"sst_refresh_method_id\": 1,\n            \"transport_protocol_id\"\
-        : 1,\n            \"max_transfers\": 2,\n            \"max_30x_redirects\"\
-        : 5,\n            \"media_encryption_mode\": \"disabled\",\n            \"\
-        stir_shaken_mode\": \"disabled\",\n            \"allowed_rtp_ips\": null\n\
-        \          }\n        },\n        \"created_at\": \"2018-12-28T15:00:43.522Z\"\
-        \n      },\n      \"relationships\": {\n        \"voice_in_trunk_group\":\
-        \ {\n          \"links\": {\n            \"self\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/24cec518-da51-4274-9a4b-1aad910b996f/relationships/voice_in_trunk_group\"\
-        ,\n            \"related\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/24cec518-da51-4274-9a4b-1aad910b996f/voice_in_trunk_group\"\
-        \n          },\n          \"data\": null\n        },\n        \"pop\": {\n\
-        \          \"links\": {\n            \"self\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/24cec518-da51-4274-9a4b-1aad910b996f/relationships/pop\"\
-        ,\n            \"related\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/24cec518-da51-4274-9a4b-1aad910b996f/pop\"\
-        \n          },\n          \"data\": {\n            \"type\": \"pops\",\n \
-        \           \"id\": \"ba7ccbef-82ac-4372-9391-eac90d5c9479\"\n          }\n\
-        \        }\n      }\n    }\n  ],\n  \"included\": [\n    {\n      \"id\":\
-        \ \"837c5764-a6c3-456f-aa37-71fc8f8ca07b\",\n      \"type\": \"voice_in_trunk_groups\"\
-        ,\n      \"attributes\": {\n        \"created_at\": \"2017-11-14T15:07:25.571Z\"\
-        ,\n        \"name\": \"sample trunk group\",\n        \"capacity_limit\":\
-        \ null\n      },\n      \"relationships\": {\n        \"voice_in_trunks\"\
-        : {\n          \"links\": {\n            \"self\": \"https://sandbox-api.didww.com/v3/voice_in_trunk_groups/837c5764-a6c3-456f-aa37-71fc8f8ca07b/relationships/voice_in_trunks\"\
-        ,\n            \"related\": \"https://sandbox-api.didww.com/v3/voice_in_trunk_groups/837c5764-a6c3-456f-aa37-71fc8f8ca07b/voice_in_trunks\"\
-        \n          }\n        }\n      },\n      \"meta\": {\n        \"trunks_count\"\
-        : 2\n      }\n    },\n    {\n      \"id\": \"ba7ccbef-82ac-4372-9391-eac90d5c9479\"\
-        ,\n      \"type\": \"pops\",\n      \"attributes\": {\n        \"name\": \"\
-        DE, FRA\"\n      }\n    }\n  ],\n  \"meta\": {\n    \"total_records\": 68\n\
-        \  },\n  \"links\": {\n    \"first\": \"https://sandbox-api.didww.com/v3/voice_in_trunks?include=trunk_group%2Cpop&page%5Bnumber%5D=1&page%5Bsize%5D=4&sort=-created_at\"\
-        ,\n    \"next\": \"https://sandbox-api.didww.com/v3/voice_in_trunks?include=trunk_group%2Cpop&page%5Bnumber%5D=2&page%5Bsize%5D=4&sort=-created_at\"\
-        ,\n    \"last\": \"https://sandbox-api.didww.com/v3/voice_in_trunks?include=trunk_group%2Cpop&page%5Bnumber%5D=18&page%5Bsize%5D=4&sort=-created_at\"\
-        \n  }\n}"
+      string: '{"data":[{"id":"2b4b1fcf-fe6a-4de9-8a58-7df46820ba13","type":"voice_in_trunks","attributes":{"priority":1,"capacity_limit":null,"weight":65535,"name":"sample trunk pstn","cli_format":"e164","cli_prefix":"","description":"","ringing_timeout":null,"configuration":{"type":"pstn_configurations","attributes":{"dst":"442080995011"}},"created_at":"2018-12-28T15:03:48.751Z"},"relationships":{"voice_in_trunk_group":{"links":{"self":"https://sandbox-api.didww.com/v3/voice_in_trunks/2b4b1fcf-fe6a-4de9-8a58-7df46820ba13/relationships/voice_in_trunk_group","related":"https://sandbox-api.didww.com/v3/voice_in_trunks/2b4b1fcf-fe6a-4de9-8a58-7df46820ba13/voice_in_trunk_group"},"data":null},"pop":{"links":{"self":"https://sandbox-api.didww.com/v3/voice_in_trunks/2b4b1fcf-fe6a-4de9-8a58-7df46820ba13/relationships/pop","related":"https://sandbox-api.didww.com/v3/voice_in_trunks/2b4b1fcf-fe6a-4de9-8a58-7df46820ba13/pop"},"data":null}}},{"id":"24cec518-da51-4274-9a4b-1aad910b996f","type":"voice_in_trunks","attributes":{"priority":1,"capacity_limit":null,"weight":65535,"name":"Sip trunk sample","cli_format":"local","cli_prefix":"","description":"","ringing_timeout":null,"configuration":{"type":"sip_configurations","attributes":{"username":"username","host":"203.0.113.78","port":8060,"codec_ids":[9,10,8],"rx_dtmf_format_id":1,"tx_dtmf_format_id":1,"resolve_ruri":true,"auth_enabled":true,"auth_user":"auth_user","auth_password":"auth_password","auth_from_user":"","auth_from_domain":"","sst_enabled":false,"sst_min_timer":600,"sst_max_timer":900,"sst_accept_501":true,"sip_timer_b":8000,"dns_srv_failover_timer":2000,"rtp_ping":false,"rtp_timeout":30,"force_symmetric_rtp":false,"symmetric_rtp_ignore_rtcp":false,"rerouting_disconnect_code_ids":null,"sst_session_expires":null,"sst_refresh_method_id":1,"transport_protocol_id":1,"max_transfers":2,"max_30x_redirects":5,"media_encryption_mode":"disabled","stir_shaken_mode":"disabled","allowed_rtp_ips":null,"enabled_sip_registration":false,"use_did_in_ruri":false,"network_protocol_priority":"any","diversion_inject_mode":"none","cnam_lookup":false,"incoming_auth_username":null,"incoming_auth_password":null,"diversion_relay_policy":"none"}},"created_at":"2018-12-28T15:00:43.522Z"},"relationships":{"voice_in_trunk_group":{"links":{"self":"https://sandbox-api.didww.com/v3/voice_in_trunks/24cec518-da51-4274-9a4b-1aad910b996f/relationships/voice_in_trunk_group","related":"https://sandbox-api.didww.com/v3/voice_in_trunks/24cec518-da51-4274-9a4b-1aad910b996f/voice_in_trunk_group"},"data":null},"pop":{"links":{"self":"https://sandbox-api.didww.com/v3/voice_in_trunks/24cec518-da51-4274-9a4b-1aad910b996f/relationships/pop","related":"https://sandbox-api.didww.com/v3/voice_in_trunks/24cec518-da51-4274-9a4b-1aad910b996f/pop"},"data":{"type":"pops","id":"ba7ccbef-82ac-4372-9391-eac90d5c9479"}}}}],"included":[{"id":"837c5764-a6c3-456f-aa37-71fc8f8ca07b","type":"voice_in_trunk_groups","attributes":{"created_at":"2017-11-14T15:07:25.571Z","name":"sample trunk group","capacity_limit":null},"relationships":{"voice_in_trunks":{"links":{"self":"https://sandbox-api.didww.com/v3/voice_in_trunk_groups/837c5764-a6c3-456f-aa37-71fc8f8ca07b/relationships/voice_in_trunks","related":"https://sandbox-api.didww.com/v3/voice_in_trunk_groups/837c5764-a6c3-456f-aa37-71fc8f8ca07b/voice_in_trunks"}}},"meta":{"trunks_count":2}},{"id":"ba7ccbef-82ac-4372-9391-eac90d5c9479","type":"pops","attributes":{"name":"DE, FRA"}}],"meta":{"total_records":68},"links":{"first":"https://sandbox-api.didww.com/v3/voice_in_trunks?include=trunk_group%2Cpop&page%5Bnumber%5D=1&page%5Bsize%5D=4&sort=-created_at","next":"https://sandbox-api.didww.com/v3/voice_in_trunks?include=trunk_group%2Cpop&page%5Bnumber%5D=2&page%5Bsize%5D=4&sort=-created_at","last":"https://sandbox-api.didww.com/v3/voice_in_trunks?include=trunk_group%2Cpop&page%5Bnumber%5D=18&page%5Bsize%5D=4&sort=-created_at"}}'
     headers:
       Content-Type:
       - application/vnd.api+json
diff --git a/tests/fixtures/voice_in_trunks/update_sip.yaml b/tests/fixtures/voice_in_trunks/update_sip.yaml
index 8288494..8273faa 100644
--- a/tests/fixtures/voice_in_trunks/update_sip.yaml
+++ b/tests/fixtures/voice_in_trunks/update_sip.yaml
@@ -12,49 +12,7 @@ interactions:
     uri: https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762
   response:
     body:
-      string: "{\n  \"data\": {\n    \"id\": \"a80006b6-4183-4865-8b99-7ebbd359a762\"\
-        ,\n    \"type\": \"voice_in_trunks\",\n    \"attributes\": {\n      \"priority\"\
-        : 1,\n      \"capacity_limit\": null,\n      \"weight\": 65535,\n      \"\
-        name\": \"hello, updated test sip trunk\",\n      \"cli_format\": \"e164\"\
-        ,\n      \"cli_prefix\": null,\n      \"description\": \"just a description\"\
-        ,\n      \"ringing_timeout\": null,\n      \"configuration\": {\n        \"\
-        type\": \"sip_configurations\",\n        \"attributes\": {\n          \"username\"\
-        : \"new-username\",\n          \"host\": \"203.0.113.110\",\n          \"\
-        port\": 5060,\n          \"codec_ids\": [\n            9,\n            10,\n\
-        \            8,\n            7,\n            6\n          ],\n          \"\
-        rx_dtmf_format_id\": 1,\n          \"tx_dtmf_format_id\": 1,\n          \"\
-        resolve_ruri\": false,\n          \"auth_enabled\": false,\n          \"auth_user\"\
-        : null,\n          \"auth_password\": null,\n          \"auth_from_user\"\
-        : null,\n          \"auth_from_domain\": null,\n          \"sst_enabled\"\
-        : false,\n          \"sst_min_timer\": 600,\n          \"sst_max_timer\":\
-        \ 900,\n          \"sst_accept_501\": true,\n          \"sip_timer_b\": 8000,\n\
-        \          \"dns_srv_failover_timer\": 2000,\n          \"rtp_ping\": false,\n\
-        \          \"rtp_timeout\": 30,\n          \"force_symmetric_rtp\": false,\n\
-        \          \"symmetric_rtp_ignore_rtcp\": false,\n          \"rerouting_disconnect_code_ids\"\
-        : [\n            56,\n            58,\n            59,\n            60,\n\
-        \            64,\n            65,\n            66,\n            67,\n    \
-        \        68,\n            69,\n            70,\n            71,\n        \
-        \    72,\n            73,\n            74,\n            75,\n            76,\n\
-        \            77,\n            78,\n            79,\n            80,\n    \
-        \        81,\n            82,\n            83,\n            84,\n        \
-        \    86,\n            87,\n            88,\n            89,\n            90,\n\
-        \            91,\n            92,\n            96,\n            97,\n    \
-        \        98,\n            99,\n            101,\n            102,\n      \
-        \      103,\n            104,\n            105,\n            106,\n      \
-        \      107,\n            108,\n            1505\n          ],\n          \"\
-        sst_session_expires\": null,\n          \"sst_refresh_method_id\": 1,\n  \
-        \        \"transport_protocol_id\": 1,\n          \"max_transfers\": 5,\n\
-        \          \"max_30x_redirects\": 0,\n          \"media_encryption_mode\"\
-        : \"zrtp\",\n          \"stir_shaken_mode\": \"pai\",\n          \"allowed_rtp_ips\"\
-        : [\n            \"203.0.113.1\"\n          ]\n        }\n      },\n      \"\
-        created_at\": \"2018-12-28T17:37:48.010Z\"\n    },\n    \"relationships\"\
-        : {\n      \"voice_in_trunk_group\": {\n        \"links\": {\n          \"\
-        self\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/relationships/voice_in_trunk_group\"\
-        ,\n          \"related\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/voice_in_trunk_group\"\
-        \n        }\n      },\n      \"pop\": {\n        \"links\": {\n          \"\
-        self\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/relationships/pop\"\
-        ,\n          \"related\": \"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/pop\"\
-        \n        }\n      }\n    }\n  }\n}"
+      string: '{"data":{"id":"a80006b6-4183-4865-8b99-7ebbd359a762","type":"voice_in_trunks","attributes":{"priority":1,"capacity_limit":null,"weight":65535,"name":"hello, updated test sip trunk","cli_format":"e164","cli_prefix":null,"description":"just a description","ringing_timeout":null,"configuration":{"type":"sip_configurations","attributes":{"username":"new-username","host":"203.0.113.110","port":5060,"codec_ids":[9,10,8,7,6],"rx_dtmf_format_id":1,"tx_dtmf_format_id":1,"resolve_ruri":false,"auth_enabled":false,"auth_user":null,"auth_password":null,"auth_from_user":null,"auth_from_domain":null,"sst_enabled":false,"sst_min_timer":600,"sst_max_timer":900,"sst_accept_501":true,"sip_timer_b":8000,"dns_srv_failover_timer":2000,"rtp_ping":false,"rtp_timeout":30,"force_symmetric_rtp":false,"symmetric_rtp_ignore_rtcp":false,"rerouting_disconnect_code_ids":[56,58,59,60,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,86,87,88,89,90,91,92,96,97,98,99,101,102,103,104,105,106,107,108,1505],"sst_session_expires":null,"sst_refresh_method_id":1,"transport_protocol_id":1,"max_transfers":5,"max_30x_redirects":0,"media_encryption_mode":"zrtp","stir_shaken_mode":"pai","allowed_rtp_ips":["203.0.113.1"],"network_protocol_priority":"force_ipv4","enabled_sip_registration":false,"use_did_in_ruri":false,"diversion_relay_policy":"none","diversion_inject_mode":"did_number","cnam_lookup":false,"incoming_auth_username":null,"incoming_auth_password":null}},"created_at":"2018-12-28T17:37:48.010Z"},"relationships":{"voice_in_trunk_group":{"links":{"self":"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/relationships/voice_in_trunk_group","related":"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/voice_in_trunk_group"}},"pop":{"links":{"self":"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/relationships/pop","related":"https://sandbox-api.didww.com/v3/voice_in_trunks/a80006b6-4183-4865-8b99-7ebbd359a762/pop"}}}}}'
     headers:
       Content-Type:
       - application/vnd.api+json
diff --git a/tests/resources/test_voice_in_trunk.py b/tests/resources/test_voice_in_trunk.py
index 4c623fa..aac0f35 100644
--- a/tests/resources/test_voice_in_trunk.py
+++ b/tests/resources/test_voice_in_trunk.py
@@ -2,7 +2,10 @@
 from didww.enums import (
     CliFormat,
     Codec,
+    DiversionInjectMode,
+    DiversionRelayPolicy,
     MediaEncryptionMode,
+    NetworkProtocolPriority,
     ReroutingDisconnectCode,
     RxDtmfFormat,
     SstRefreshMethod,
@@ -194,6 +197,15 @@ def test_create_sip_trunk_with_rerouting_disconnect_codes(self, client):
         config.media_encryption_mode = MediaEncryptionMode.ZRTP
         config.stir_shaken_mode = StirShakenMode.PAI
         config.allowed_rtp_ips = ["203.0.113.1"]
+        # API 2026-04-16 writable attributes
+        config.diversion_relay_policy = DiversionRelayPolicy.AS_IS
+        config.diversion_inject_mode = DiversionInjectMode.DID_NUMBER
+        config.network_protocol_priority = NetworkProtocolPriority.FORCE_IPV4
+        config.cnam_lookup = True
+        # use_did_in_ruri must stay false unless enabled_sip_registration is
+        # also True (server returns 422 otherwise).  Setting it here is
+        # redundant against the default but documents the field.
+        config.use_did_in_ruri = False
 
         trunk = VoiceInTrunk()
         trunk.name = "hello, test sip trunk"
@@ -247,7 +259,237 @@ def test_update_voice_in_trunk_sip(self, client):
         assert sip_config.username == "new-username"
         assert sip_config.max_transfers == 5
 
+    @my_vcr.use_cassette("voice_in_trunks/create_with_sip_registration.yaml")
+    def test_create_voice_in_trunk_with_sip_registration_returns_populated_credentials(self, client):
+        """End-to-end: when the SDK sends ``enabled_sip_registration: True`` the
+        server returns 201 with server-generated ``incoming_auth_username`` and
+        ``incoming_auth_password``. The SDK must surface those populated values
+        to the caller, not None."""
+        config = SipConfiguration()
+        config.enabled_sip_registration = True
+        config.use_did_in_ruri = True
+        config.cnam_lookup = True
+        config.diversion_relay_policy = DiversionRelayPolicy.AS_IS
+        config.diversion_inject_mode = DiversionInjectMode.DID_NUMBER
+        config.network_protocol_priority = NetworkProtocolPriority.PREFER_IPV4
+
+        trunk = VoiceInTrunk()
+        trunk.name = "sip-registration"
+        trunk.priority = 1
+        trunk.weight = 100
+        trunk.cli_format = CliFormat.E164
+        trunk.ringing_timeout = 30
+        trunk.configuration = config
+
+        response = client.voice_in_trunks().create(trunk)
+        created = response.data
+        sip_config = created.configuration
+        assert isinstance(sip_config, SipConfiguration)
+        assert sip_config.enabled_sip_registration is True
+        # Server-generated credentials are populated, not None.
+        assert sip_config.incoming_auth_username
+        assert sip_config.incoming_auth_password
+
+    @my_vcr.use_cassette("voice_in_trunks/disable_sip_registration.yaml")
+    def test_disable_sip_registration_patch_serializes_all_three_fields(self, client):
+        """Disabling SIP registration is a multi-field PATCH because the
+        server returns 422 for any request that flips
+        ``enabled_sip_registration`` to false without simultaneously
+        providing a non-blank ``host`` and ``use_did_in_ruri: False``.
+        Lock those three fields in the same request body — the cassette
+        matches on body, so a future regression that drops one of them
+        fails the request match."""
+        config = SipConfiguration()
+        config.enabled_sip_registration = False
+        config.use_did_in_ruri = False
+        config.host = "203.0.113.10"
+
+        trunk = VoiceInTrunk()
+        trunk.id = "57a939dd-1600-41a6-80b1-f624e22a1f4c"
+        trunk.configuration = config
+
+        response = client.voice_in_trunks().update(trunk)
+        sip_config = response.data.configuration
+        assert isinstance(sip_config, SipConfiguration)
+        assert sip_config.enabled_sip_registration is False
+        assert sip_config.use_did_in_ruri is False
+        assert sip_config.host == "203.0.113.10"
+        assert sip_config.incoming_auth_username is None
+        assert sip_config.incoming_auth_password is None
+
     @my_vcr.use_cassette("voice_in_trunks/delete.yaml")
     def test_delete_voice_in_trunk(self, client):
         result = client.voice_in_trunks().delete("41b94706-325e-4704-a433-d65105758836")
         assert result is None
+
+    # 2026-04-16 SIP-registration attributes (API 2026-04-16).
+    #
+    # Real wire shape captured from sandbox: when sip_registration is
+    # enabled, host/port/username come back as null and the API rejects
+    # any attempt to set them, so the test fixtures below intentionally
+    # omit them.
+    def test_sip_configuration_writable_registration_attributes_serialize(self):
+        from didww.enums import DiversionInjectMode, NetworkProtocolPriority
+
+        config = SipConfiguration(
+            attributes={
+                "enabled_sip_registration": True,
+                "use_did_in_ruri": True,
+                "cnam_lookup": True,
+                "diversion_inject_mode": "did_number",
+                "network_protocol_priority": "prefer_ipv4",
+            }
+        )
+        assert config.enabled_sip_registration is True
+        assert config.use_did_in_ruri is True
+        assert config.cnam_lookup is True
+        assert config.diversion_inject_mode == DiversionInjectMode.DID_NUMBER
+        assert config.network_protocol_priority == NetworkProtocolPriority.PREFER_IPV4
+
+        payload = config.to_jsonapi()
+        assert payload["type"] == "sip_configurations"
+        assert payload["attributes"]["enabled_sip_registration"] is True
+        assert payload["attributes"]["use_did_in_ruri"] is True
+        assert payload["attributes"]["cnam_lookup"] is True
+        assert payload["attributes"]["diversion_inject_mode"] == "did_number"
+        assert payload["attributes"]["network_protocol_priority"] == "prefer_ipv4"
+
+    def test_sip_configuration_exposes_read_only_incoming_auth_credentials(self):
+        # Test fixture values; not a real credential. NOSONAR-suppressed below.
+        fake_user = "sipreg-user-1"
+        fake_pass = "s3cret-Pa55"  # NOSONAR python:S2068 -- test fixture
+        config = SipConfiguration(
+            attributes={
+                "host": None,
+                "port": None,
+                "username": None,
+                "enabled_sip_registration": True,
+                "incoming_auth_username": fake_user,
+                "incoming_auth_password": fake_pass,
+            }
+        )
+        assert config.incoming_auth_username == fake_user
+        assert config.incoming_auth_password == fake_pass
+
+    def test_sip_configuration_strips_read_only_credentials_from_write_payload(self):
+        # Simulate a caller who loaded a SIP configuration from the server
+        # (with incoming_auth_* populated) and submits it back. The server
+        # returns 400 Param not allowed if these are echoed in the request,
+        # so the SDK MUST strip them from the JSON:API payload.
+        fake_user = "sipreg-user-1"
+        fake_pass = "s3cret-Pa55"  # NOSONAR python:S2068 -- test fixture
+        config = SipConfiguration(
+            attributes={
+                "enabled_sip_registration": True,
+                "use_did_in_ruri": True,
+                "incoming_auth_username": fake_user,
+                "incoming_auth_password": fake_pass,
+            }
+        )
+        payload = config.to_jsonapi()
+        assert payload["attributes"]["enabled_sip_registration"] is True
+        assert payload["attributes"]["use_did_in_ruri"] is True
+        assert "incoming_auth_username" not in payload["attributes"]
+        assert "incoming_auth_password" not in payload["attributes"]
+
+    def test_enabling_sip_registration_clears_host_and_port(self):
+        cfg = SipConfiguration(attributes={"host": "sip.example.com", "port": 5060})
+        cfg.enabled_sip_registration = True
+        assert cfg.host is None
+        assert cfg._attr("port") is None
+        assert cfg.enabled_sip_registration is True
+
+    def test_enabling_sip_registration_emits_host_and_port_on_fresh_config(self):
+        # Regression: PATCH against an existing trunk that already has a
+        # host on the server side. The local SipConfiguration starts empty,
+        # so nothing is in the local _attributes dict. Setting
+        # enabled_sip_registration = True must still emit host=None /
+        # port=None on the wire — otherwise the server merges the new field
+        # with the persisted host and rejects with 422.
+        cfg = SipConfiguration()
+        cfg.enabled_sip_registration = True
+        attrs = cfg.to_jsonapi()["attributes"]
+        assert "host" in attrs
+        assert attrs["host"] is None
+        assert "port" in attrs
+        assert attrs["port"] is None
+        assert attrs["enabled_sip_registration"] is True
+
+    def test_disabling_sip_registration_forces_use_did_in_ruri_to_false(self):
+        cfg = SipConfiguration(
+            attributes={"enabled_sip_registration": True, "use_did_in_ruri": True}
+        )
+        cfg.enabled_sip_registration = False
+        assert cfg.enabled_sip_registration is False
+        assert cfg.use_did_in_ruri is False
+
+    def test_setting_host_disables_sip_registration_and_use_did_in_ruri(self):
+        cfg = SipConfiguration(
+            attributes={"enabled_sip_registration": True, "use_did_in_ruri": True}
+        )
+        cfg.host = "sip.example.com"
+        assert cfg.host == "sip.example.com"
+        assert cfg.enabled_sip_registration is False
+        assert cfg.use_did_in_ruri is False
+
+    def test_enabling_sip_registration_leaves_use_did_in_ruri_untouched(self):
+        cfg = SipConfiguration(
+            attributes={"enabled_sip_registration": True, "use_did_in_ruri": True}
+        )
+        cfg.enabled_sip_registration = True
+        assert cfg.use_did_in_ruri is True
+
+    def test_sip_configuration_wire_payload_reflects_cascaded_state(self):
+        # Mirror dimension: after the cascade fires from a property setter,
+        # the on-the-wire payload (to_jsonapi output) must contain the
+        # cascaded field values, not just the in-memory state.
+        cfg = SipConfiguration(attributes={
+            "enabled_sip_registration": True,
+            "use_did_in_ruri": True,
+        })
+        cfg.host = "sip.example.com"  # triggers cascade
+        attrs = cfg.to_jsonapi()["attributes"]
+        assert attrs["host"] == "sip.example.com"
+        assert attrs["enabled_sip_registration"] is False
+        assert attrs["use_did_in_ruri"] is False
+
+    def test_constructor_assignment_bypasses_cascade_for_server_response_shapes(self):
+        # Server may return a regular SIP trunk shape (host: present together
+        # with use_did_in_ruri: True). SipConfiguration(attributes=...) sets
+        # _attributes directly, bypassing the property setters — without that
+        # bypass, deserializing already-consistent server data would clobber
+        # the use_did_in_ruri value.
+        cfg = SipConfiguration(attributes={
+            "host": "sip.example.com",
+            "port": 5060,
+            "enabled_sip_registration": False,
+            "use_did_in_ruri": True,
+        })
+        assert cfg.host == "sip.example.com"
+        assert cfg._attr("port") == 5060
+        assert cfg.enabled_sip_registration is False
+        assert cfg.use_did_in_ruri is True
+
+    def test_sip_configuration_repr_redacts_credentials(self):
+        # Default __repr__ output is what shows up in default print() /
+        # logging / unhandled exception traces — none of those contexts
+        # should ever expose SIP credentials in plaintext.
+        secret_pass = "s3cret-Pa55"  # NOSONAR python:S2068 -- test fixture
+        secret_inc_pass = "srv-pass-xyz"  # NOSONAR python:S2068
+        config = SipConfiguration(
+            attributes={
+                "username": "alice",
+                "host": "sip.example.com",
+                "auth_password": secret_pass,
+                "enabled_sip_registration": True,
+                "incoming_auth_username": "srv-user-xyz",
+                "incoming_auth_password": secret_inc_pass,
+            }
+        )
+        output = repr(config)
+        assert "alice" in output
+        assert "sip.example.com" in output
+        assert secret_pass not in output
+        assert "srv-user-xyz" not in output
+        assert secret_inc_pass not in output
+        assert "[FILTERED]" in output