diff --git a/lib/paho/mqtt/__init__.py b/lib/paho/mqtt/__init__.py
index 19b6a4ab..377cecc7 100644
--- a/lib/paho/mqtt/__init__.py
+++ b/lib/paho/mqtt/__init__.py
@@ -1,4 +1,4 @@
-__version__ = "2.0.0"
+__version__ = "2.1.0"
 
 
 class MQTTException(Exception):
diff --git a/lib/paho/mqtt/client.py b/lib/paho/mqtt/client.py
index f5897328..4ccc8696 100644
--- a/lib/paho/mqtt/client.py
+++ b/lib/paho/mqtt/client.py
@@ -288,7 +288,7 @@ class WebsocketConnectionError(ConnectionError):
     pass
 
 
-def error_string(mqtt_errno: MQTTErrorCode) -> str:
+def error_string(mqtt_errno: MQTTErrorCode | int) -> str:
     """Return the error string associated with an mqtt error number."""
     if mqtt_errno == MQTT_ERR_SUCCESS:
         return "No error."
@@ -465,7 +465,7 @@ def _force_bytes(s: str | bytes) -> bytes:
     return s
 
 
-def _encode_payload(payload: str | bytes | bytearray | int | float | None) -> bytes:
+def _encode_payload(payload: str | bytes | bytearray | int | float | None) -> bytes|bytearray:
     if isinstance(payload, str):
         return payload.encode("utf-8")
 
@@ -648,7 +648,7 @@ class Client:
 
     :param CallbackAPIVersion callback_api_version: define the API version for user-callback (on_connect, on_publish,...).
         This field is required and it's recommended to use the latest version (CallbackAPIVersion.API_VERSION2).
-        See each callback for description of API for each version. The file migrations.md contains details on
+        See each callback for description of API for each version. The file docs/migrations.rst contains details on
         how to migrate between version.
 
     :param str client_id: the unique client id string used when connecting to the
@@ -682,6 +682,10 @@ class Client:
 
     :param transport: use "websockets" to use WebSockets as the transport
         mechanism. Set to "tcp" to use raw TCP, which is the default.
+        Use "unix" to use Unix sockets as the transport mechanism; note that
+        this option is only available on platforms that support Unix sockets,
+        and the "host" argument is interpreted as the path to the Unix socket
+        file in this case.
 
     :param bool manual_ack: normally, when a message is received, the library automatically
         acknowledges after on_message callback returns.  manual_ack=True allows the application to
@@ -728,19 +732,21 @@ class Client:
 
     def __init__(
         self,
-        callback_api_version: CallbackAPIVersion,
-        client_id: str = "",
+        callback_api_version: CallbackAPIVersion = CallbackAPIVersion.VERSION1,
+        client_id: str | None = "",
         clean_session: bool | None = None,
         userdata: Any = None,
-        protocol: int = MQTTv311,
-        transport: Literal["tcp", "websockets"] = "tcp",
+        protocol: MQTTProtocolVersion = MQTTv311,
+        transport: Literal["tcp", "websockets", "unix"] = "tcp",
         reconnect_on_failure: bool = True,
         manual_ack: bool = False,
     ) -> None:
         transport = transport.lower()  # type: ignore
-        if transport not in ("websockets", "tcp"):
+        if transport == "unix" and not hasattr(socket, "AF_UNIX"):
+            raise ValueError('"unix" transport not supported')
+        elif transport not in ("websockets", "tcp", "unix"):
             raise ValueError(
-                f'transport must be "websockets" or "tcp", not {transport}')
+                f'transport must be "websockets", "tcp" or "unix", not {transport}')
 
         self._manual_ack = manual_ack
         self._transport = transport
@@ -764,7 +770,7 @@ class Client:
             # Help user to migrate, it probably provided a client id
             # as first arguments
             raise ValueError(
-                "Unsupported callback API version: version 2.0 added a callback_api_version, see migrations.md for details"
+                "Unsupported callback API version: version 2.0 added a callback_api_version, see docs/migrations.rst for details"
             )
         if self._callback_api_version not in CallbackAPIVersion:
             raise ValueError("Unsupported callback API version")
@@ -931,7 +937,7 @@ class Client:
         self._keepalive = value
 
     @property
-    def transport(self) -> Literal["tcp", "websockets"]:
+    def transport(self) -> Literal["tcp", "websockets", "unix"]:
         """
         Transport method used for the connection ("tcp" or "websockets").
 
@@ -953,7 +959,7 @@ class Client:
 
         This property is read-only.
         """
-        return self.protocol
+        return self._protocol
 
     @property
     def connect_timeout(self) -> float:
@@ -2032,7 +2038,7 @@ class Client:
         return self._send_subscribe(False, topic_qos_list, properties)
 
     def unsubscribe(
-        self, topic: str, properties: Properties | None = None
+        self, topic: str | list[str], properties: Properties | None = None
     ) -> tuple[MQTTErrorCode, int | None]:
         """Unsubscribe the client from one or more topics.
 
@@ -2356,7 +2362,6 @@ class Client:
         self._thread_terminate = True
         if threading.current_thread() != self._thread:
             self._thread.join()
-            self._thread = None
 
         return MQTTErrorCode.MQTT_ERR_SUCCESS
 
@@ -2445,7 +2450,7 @@ class Client:
 
                 connect_callback(client, userdata, flags, rc)
 
-            * For MQTT it's v5.0::
+            * For MQTT v5.0 it's::
 
                 connect_callback(client, userdata, flags, reason_code, properties)
 
@@ -2732,7 +2737,7 @@ class Client:
 
                 disconnect_callback(client, userdata, rc)
 
-            * For MQTT it's v5.0::
+            * For MQTT v5.0 it's::
 
                 disconnect_callback(client, userdata, reason_code, properties)
 
@@ -3363,7 +3368,7 @@ class Client:
         self,
         mid: int,
         topic: bytes,
-        payload: bytes = b"",
+        payload: bytes|bytearray = b"",
         qos: int = 0,
         retain: bool = False,
         dup: bool = False,
@@ -3373,7 +3378,7 @@ class Client:
         # we assume that topic and payload are already properly encoded
         if not isinstance(topic, bytes):
             raise TypeError('topic must be bytes, not str')
-        if payload and not isinstance(payload, bytes):
+        if payload and not isinstance(payload, (bytes, bytearray)):
             raise TypeError('payload must be bytes if set')
 
         if self._sock is None:
@@ -3462,7 +3467,7 @@ class Client:
         return self._packet_queue(command, packet, 0, 0)
 
     def _send_connect(self, keepalive: int) -> MQTTErrorCode:
-        proto_ver = self._protocol
+        proto_ver = int(self._protocol)
         # hard-coded UTF-8 encoded string
         protocol = b"MQTT" if proto_ver >= MQTTv311 else b"MQIsdp"
 
@@ -4514,7 +4519,10 @@ class Client:
                         MQTT_LOG_ERR, 'Caught exception in on_connect_fail: %s', err)
 
     def _thread_main(self) -> None:
-        self.loop_forever(retry_first_connection=True)
+        try:
+            self.loop_forever(retry_first_connection=True)
+        finally:
+            self._thread = None
 
     def _reconnect_wait(self) -> None:
         # See reconnect_delay_set for details
@@ -4595,7 +4603,11 @@ class Client:
         return None
 
     def _create_socket(self) -> SocketLike:
-        sock = self._create_socket_connection()
+        if self._transport == "unix":
+            sock = self._create_unix_socket_connection()
+        else:
+            sock = self._create_socket_connection()
+
         if self._ssl:
             sock = self._ssl_wrap_socket(sock)
 
@@ -4612,6 +4624,11 @@ class Client:
 
         return sock
 
+    def _create_unix_socket_connection(self) -> _socket.socket:
+        unix_socket = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+        unix_socket.connect(self._host)
+        return unix_socket
+
     def _create_socket_connection(self) -> _socket.socket:
         proxy = self._get_proxy()
         addr = (self._host, self._port)
diff --git a/lib/paho/mqtt/publish.py b/lib/paho/mqtt/publish.py
index 42435156..333c190a 100644
--- a/lib/paho/mqtt/publish.py
+++ b/lib/paho/mqtt/publish.py
@@ -24,7 +24,7 @@ import collections
 from collections.abc import Iterable
 from typing import TYPE_CHECKING, Any, List, Tuple, Union
 
-from paho.mqtt.enums import CallbackAPIVersion
+from paho.mqtt.enums import CallbackAPIVersion, MQTTProtocolVersion
 from paho.mqtt.properties import Properties
 from paho.mqtt.reasoncodes import ReasonCode
 
@@ -112,7 +112,7 @@ def multiple(
     will: MessageDict | None = None,
     auth: AuthParameter | None = None,
     tls: TLSParameter | None = None,
-    protocol: int = paho.MQTTv311,
+    protocol: MQTTProtocolVersion = paho.MQTTv311,
     transport: Literal["tcp", "websockets"] = "tcp",
     proxy_args: Any | None = None,
 ) -> None:
@@ -240,7 +240,7 @@ def single(
     will: MessageDict | None = None,
     auth: AuthParameter | None = None,
     tls: TLSParameter | None = None,
-    protocol: int = paho.MQTTv311,
+    protocol: MQTTProtocolVersion = paho.MQTTv311,
     transport: Literal["tcp", "websockets"] = "tcp",
     proxy_args: Any | None = None,
 ) -> None:
diff --git a/lib/paho/mqtt/reasoncodes.py b/lib/paho/mqtt/reasoncodes.py
index 6b30cb83..243ac96f 100644
--- a/lib/paho/mqtt/reasoncodes.py
+++ b/lib/paho/mqtt/reasoncodes.py
@@ -30,7 +30,7 @@ class ReasonCode:
 
     """
 
-    def __init__(self, packetType, aName="Success", identifier=-1):
+    def __init__(self, packetType: int, aName: str ="Success", identifier: int =-1):
         """
         packetType: the type of the packet, such as PacketTypes.CONNECT that
             this reason code will be used with.  Some reason codes have different
diff --git a/requirements.txt b/requirements.txt
index 590f4fc1..f2d316c2 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -24,7 +24,7 @@ Mako==1.3.3
 MarkupSafe==2.1.5
 musicbrainzngs==0.7.1
 packaging==24.0
-paho-mqtt==2.0.0
+paho-mqtt==2.1.0
 platformdirs==4.2.1
 plexapi==4.15.12
 portend==3.2.0