diff --git a/src/ahttpx/__init__.py b/src/ahttpx/__init__.py
index 478a50b..cc779d6 100644
--- a/src/ahttpx/__init__.py
+++ b/src/ahttpx/__init__.py
@@ -6,7 +6,7 @@
 from ._parsers import *  # HTTPParser, HTTPStream, ProtocolError
 from ._pool import *  # Connection, ConnectionPool, Transport
 from ._quickstart import *  # get, post, put, patch, delete
-from ._response import *  # Response
+from ._response import *  # StatusCode, Response
 from ._request import *  # Method, Request
 from ._streams import *  # ByteStream, DuplexStream, FileStream, Stream
 from ._server import *  # serve_http, run
@@ -47,6 +47,7 @@
     "Request",
     "run",
     "serve_http",
+    "StatusCode",
     "Stream",
     "Text",
     "timeout",
diff --git a/src/ahttpx/_client.py b/src/ahttpx/_client.py
index 45c46b9..46c9bb9 100644
--- a/src/ahttpx/_client.py
+++ b/src/ahttpx/_client.py
@@ -35,7 +35,7 @@ def build_request(
         self,
         method: Method | str,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ) -> Request:
         return Request(
@@ -49,7 +49,7 @@ async def request(
         self,
         method: Method | str,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ) -> Response:
         request = self.build_request(method, url, headers=headers, content=content)
@@ -61,7 +61,7 @@ async def stream(
         self,
         method: Method | str,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ) -> Response:
         request = self.build_request(method, url, headers=headers, content=content)
@@ -70,14 +70,14 @@ async def stream(
     async def get(
         self,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
     ):
         return await self.request("GET", url, headers=headers)
 
     async def post(
         self,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ):
         return await self.request("POST", url, headers=headers, content=content)
@@ -85,7 +85,7 @@ async def post(
     async def put(
         self,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ):
         return await self.request("PUT", url, headers=headers, content=content)
@@ -93,7 +93,7 @@ async def put(
     async def patch(
         self,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ):
         return await self.request("PATCH", url, headers=headers, content=content)
@@ -101,7 +101,7 @@ async def patch(
     async def delete(
         self,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
     ):
         return await self.request("DELETE", url, headers=headers)
 
diff --git a/src/ahttpx/_headers.py b/src/ahttpx/_headers.py
index dade805..857754f 100644
--- a/src/ahttpx/_headers.py
+++ b/src/ahttpx/_headers.py
@@ -169,6 +169,12 @@ def copy_update(self, update: "Headers" | typing.Mapping[str, str] | None) -> "H
 
         return Headers(h)
 
+    def as_byte_pairs(self) -> list[tuple[bytes, bytes]]:
+        return [
+            (k.encode('ascii'), v.encode('ascii'))
+            for k, v in self.items()
+        ]
+
     def __getitem__(self, key: str) -> str:
         match = key.lower()
         for k, v in self._dict.items():
diff --git a/src/ahttpx/_pool.py b/src/ahttpx/_pool.py
index a322c84..c4838da 100644
--- a/src/ahttpx/_pool.py
+++ b/src/ahttpx/_pool.py
@@ -185,7 +185,7 @@ async def request(
         self,
         method: Method | str,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ) -> Response:
         url = self._origin.join(url)
@@ -198,7 +198,7 @@ async def stream(
         self,
         method: Method | str,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ) -> Response:
         url = self._origin.join(url)
@@ -211,10 +211,7 @@ async def _send_head(self, request: Request) -> None:
         target = request.url.target.encode('ascii')
         protocol = b'HTTP/1.1'
         await self._parser.send_method_line(method, target, protocol)
-        headers = [
-            (k.encode('ascii'), v.encode('ascii'))
-            for k, v in request.headers.items()
-        ]
+        headers = request.headers.as_byte_pairs()
         await self._parser.send_headers(headers)
 
     async def _send_body(self, request: Request) -> None:
diff --git a/src/ahttpx/_quickstart.py b/src/ahttpx/_quickstart.py
index 8b6e12f..045b9f1 100644
--- a/src/ahttpx/_quickstart.py
+++ b/src/ahttpx/_quickstart.py
@@ -12,14 +12,14 @@
 
 async def get(
     url: URL | str,
-    headers: Headers | typing.Mapping[str, str] | None = None,
+    headers: Headers | dict[str, str] | None = None,
 ):
     async with Client() as client:
         return await client.request("GET", url=url, headers=headers)
 
 async def post(
     url: URL | str,
-    headers: Headers | typing.Mapping[str, str] | None = None,
+    headers: Headers | dict[str, str] | None = None,
     content: Content | Stream | bytes | None = None,
 ):
     async with Client() as client:
@@ -27,7 +27,7 @@ async def post(
 
 async def put(
     url: URL | str,
-    headers: Headers | typing.Mapping[str, str] | None = None,
+    headers: Headers | dict[str, str] | None = None,
     content: Content | Stream | bytes | None = None,
 ):
     async with Client() as client:
@@ -35,7 +35,7 @@ async def put(
 
 async def patch(
     url: URL | str,
-    headers: Headers | typing.Mapping[str, str] | None = None,
+    headers: Headers | dict[str, str] | None = None,
     content: Content | Stream | bytes | None = None,
 ):
     async with Client() as client:
@@ -43,7 +43,7 @@ async def patch(
 
 async def delete(
     url: URL | str,
-    headers: Headers | typing.Mapping[str, str] | None = None,
+    headers: Headers | dict[str, str] | None = None,
 ):
     async with Client() as client:
         return await client.request("DELETE", url=url, headers=headers)
diff --git a/src/ahttpx/_request.py b/src/ahttpx/_request.py
index b5f1345..8f836b5 100644
--- a/src/ahttpx/_request.py
+++ b/src/ahttpx/_request.py
@@ -6,7 +6,7 @@
 from ._headers import Headers
 from ._urls import URL
 
-__all__ = ["Request"]
+__all__ = ["Method", "Request"]
 
 
 class Method:
@@ -35,7 +35,7 @@ def __init__(
         self,
         method: Method | str,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ):
         self.method = Method(method) if not isinstance(method, Method) else method
diff --git a/src/ahttpx/_response.py b/src/ahttpx/_response.py
index d695488..c2420a7 100644
--- a/src/ahttpx/_response.py
+++ b/src/ahttpx/_response.py
@@ -7,84 +7,137 @@
 
 __all__ = ["Response"]
 
-# We're using the same set as stdlib `http.HTTPStatus` here...
-#
-# https://github.com/python/cpython/blob/main/Lib/http/__init__.py
-_codes = {
-    100: "Continue",
-    101: "Switching Protocols",
-    102: "Processing",
-    103: "Early Hints",
-    200: "OK",
-    201: "Created",
-    202: "Accepted",
-    203: "Non-Authoritative Information",
-    204: "No Content",
-    205: "Reset Content",
-    206: "Partial Content",
-    207: "Multi-Status",
-    208: "Already Reported",
-    226: "IM Used",
-    300: "Multiple Choices",
-    301: "Moved Permanently",
-    302: "Found",
-    303: "See Other",
-    304: "Not Modified",
-    305: "Use Proxy",
-    307: "Temporary Redirect",
-    308: "Permanent Redirect",
-    400: "Bad Request",
-    401: "Unauthorized",
-    402: "Payment Required",
-    403: "Forbidden",
-    404: "Not Found",
-    405: "Method Not Allowed",
-    406: "Not Acceptable",
-    407: "Proxy Authentication Required",
-    408: "Request Timeout",
-    409: "Conflict",
-    410: "Gone",
-    411: "Length Required",
-    412: "Precondition Failed",
-    413: "Content Too Large",
-    414: "URI Too Long",
-    415: "Unsupported Media Type",
-    416: "Range Not Satisfiable",
-    417: "Expectation Failed",
-    418: "I'm a Teapot",
-    421: "Misdirected Request",
-    422: "Unprocessable Content",
-    423: "Locked",
-    424: "Failed Dependency",
-    425: "Too Early",
-    426: "Upgrade Required",
-    428: "Precondition Required",
-    429: "Too Many Requests",
-    431: "Request Header Fields Too Large",
-    451: "Unavailable For Legal Reasons",
-    500: "Internal Server Error",
-    501: "Not Implemented",
-    502: "Bad Gateway",
-    503: "Service Unavailable",
-    504: "Gateway Timeout",
-    505: "HTTP Version Not Supported",
-    506: "Variant Also Negotiates",
-    507: "Insufficient Storage",
-    508: "Loop Detected",
-    510: "Not Extended",
-    511: "Network Authentication Required",
-}
+
+class StatusCode:
+    # We're using the same set as stdlib `http.HTTPStatus` here...
+    #
+    # https://github.com/python/cpython/blob/main/Lib/http/__init__.py
+    _codes = {
+        100: "Continue",
+        101: "Switching Protocols",
+        102: "Processing",
+        103: "Early Hints",
+        200: "OK",
+        201: "Created",
+        202: "Accepted",
+        203: "Non-Authoritative Information",
+        204: "No Content",
+        205: "Reset Content",
+        206: "Partial Content",
+        207: "Multi-Status",
+        208: "Already Reported",
+        226: "IM Used",
+        300: "Multiple Choices",
+        301: "Moved Permanently",
+        302: "Found",
+        303: "See Other",
+        304: "Not Modified",
+        305: "Use Proxy",
+        307: "Temporary Redirect",
+        308: "Permanent Redirect",
+        400: "Bad Request",
+        401: "Unauthorized",
+        402: "Payment Required",
+        403: "Forbidden",
+        404: "Not Found",
+        405: "Method Not Allowed",
+        406: "Not Acceptable",
+        407: "Proxy Authentication Required",
+        408: "Request Timeout",
+        409: "Conflict",
+        410: "Gone",
+        411: "Length Required",
+        412: "Precondition Failed",
+        413: "Content Too Large",
+        414: "URI Too Long",
+        415: "Unsupported Media Type",
+        416: "Range Not Satisfiable",
+        417: "Expectation Failed",
+        418: "I'm a Teapot",
+        421: "Misdirected Request",
+        422: "Unprocessable Content",
+        423: "Locked",
+        424: "Failed Dependency",
+        425: "Too Early",
+        426: "Upgrade Required",
+        428: "Precondition Required",
+        429: "Too Many Requests",
+        431: "Request Header Fields Too Large",
+        451: "Unavailable For Legal Reasons",
+        500: "Internal Server Error",
+        501: "Not Implemented",
+        502: "Bad Gateway",
+        503: "Service Unavailable",
+        504: "Gateway Timeout",
+        505: "HTTP Version Not Supported",
+        506: "Variant Also Negotiates",
+        507: "Insufficient Storage",
+        508: "Loop Detected",
+        510: "Not Extended",
+        511: "Network Authentication Required",
+    }
+
+    def __init__(self, status_code: int):
+        if status_code < 100 or status_code > 999:
+            raise ValueError("Invalid status code {status_code!r}")
+        self.value = status_code
+        self.reason_phrase = self._codes.get(status_code, "Unknown Status Code")
+
+    def is_1xx_informational(self) -> bool:
+        """
+        Returns `True` for 1xx status codes, `False` otherwise.
+        """
+        return 100 <= int(self) <= 199
+
+    def is_2xx_success(self) -> bool:
+        """
+        Returns `True` for 2xx status codes, `False` otherwise.
+        """
+        return 200 <= int(self) <= 299
+
+    def is_3xx_redirect(self) -> bool:
+        """
+        Returns `True` for 3xx status codes, `False` otherwise.
+        """
+        return 300 <= int(self) <= 399
+
+    def is_4xx_client_error(self) -> bool:
+        """
+        Returns `True` for 4xx status codes, `False` otherwise.
+        """
+        return 400 <= int(self) <= 499
+
+    def is_5xx_server_error(self) -> bool:
+        """
+        Returns `True` for 5xx status codes, `False` otherwise.
+        """
+        return 500 <= int(self) <= 599
+
+    def as_tuple(self) -> tuple[int, bytes]:
+        return (self.value, self.reason_phrase.encode('ascii'))
+
+    def __eq__(self, other) -> bool:
+        return int(self) == int(other)
+
+    def __int__(self) -> int:
+        return self.value
+
+    def __str__(self) -> str:
+        return f"{self.value} {self.reason_phrase}"
+
+    def __repr__(self) -> str:
+        return f"<StatusCode [{self.value} {self.reason_phrase}]>"
 
 
 class Response:
     def __init__(
         self,
-        status_code: int,
+        status_code: StatusCode | int,
         *,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ):
-        self.status_code = status_code
+        self.status_code = StatusCode(status_code) if not isinstance(status_code, StatusCode) else status_code
         self.headers = Headers(headers) if not isinstance(headers, Headers) else headers
         self.stream: Stream = ByteStream(b"")
 
@@ -106,17 +159,13 @@ def __init__(
         # All 1xx (informational), 204 (no content), and 304 (not modified) responses
         # MUST NOT include a message-body. All other responses do include a
         # message-body, although it MAY be of zero length.
-        if status_code >= 200 and status_code != 204 and status_code != 304:
+        if not(self.status_code.is_1xx_informational() or self.status_code == 204 or self.status_code == 304):
             content_length: int | None = self.stream.size
             if content_length is None:
                 self.headers = self.headers.copy_set("Transfer-Encoding", "chunked")
             else:
                 self.headers = self.headers.copy_set("Content-Length", str(content_length))
 
-    @property
-    def reason_phrase(self):
-        return _codes.get(self.status_code, "Unknown Status Code")
-
     @property
     def body(self) -> bytes:
         if not hasattr(self, '_body'):
@@ -155,4 +204,4 @@ async def __aexit__(self,
         await self.close()
 
     def __repr__(self):
-        return f"<Response [{self.status_code} {self.reason_phrase}]>"
+        return f"<Response [{int(self.status_code)} {self.status_code.reason_phrase}]>"
diff --git a/src/ahttpx/_server.py b/src/ahttpx/_server.py
index 973da54..577d001 100644
--- a/src/ahttpx/_server.py
+++ b/src/ahttpx/_server.py
@@ -37,7 +37,7 @@ async def handle_requests(self):
                 async with Request(method, url, headers=headers, content=stream) as request:
                     try:
                         response = await self._endpoint(request)
-                        status_line = f"{request.method} {request.url.target} [{response.status_code} {response.reason_phrase}]"
+                        status_line = f"{request.method} {request.url.target} [{response.status_code} {response.status_code.reason_phrase}]"
                         logger.info(status_line)
                     except Exception:
                         logger.error("Internal Server Error", exc_info=True)
@@ -72,13 +72,9 @@ async def _recv_body(self):
     # Return the response...
     async def _send_head(self, response: Response):
         protocol = b"HTTP/1.1"
-        status = response.status_code
-        reason = response.reason_phrase.encode('ascii')
+        status, reason = response.status_code.as_tuple()
         await self._parser.send_status_line(protocol, status, reason)
-        headers = [
-            (k.encode('ascii'), v.encode('ascii'))
-            for k, v in response.headers.items()
-        ]
+        headers = response.headers.as_byte_pairs()
         await self._parser.send_headers(headers)
 
     async def _send_body(self, response: Response):
diff --git a/src/httpx/__init__.py b/src/httpx/__init__.py
index 478a50b..cc779d6 100644
--- a/src/httpx/__init__.py
+++ b/src/httpx/__init__.py
@@ -6,7 +6,7 @@
 from ._parsers import *  # HTTPParser, HTTPStream, ProtocolError
 from ._pool import *  # Connection, ConnectionPool, Transport
 from ._quickstart import *  # get, post, put, patch, delete
-from ._response import *  # Response
+from ._response import *  # StatusCode, Response
 from ._request import *  # Method, Request
 from ._streams import *  # ByteStream, DuplexStream, FileStream, Stream
 from ._server import *  # serve_http, run
@@ -47,6 +47,7 @@
     "Request",
     "run",
     "serve_http",
+    "StatusCode",
     "Stream",
     "Text",
     "timeout",
diff --git a/src/httpx/_client.py b/src/httpx/_client.py
index aaf8ad9..07091a7 100644
--- a/src/httpx/_client.py
+++ b/src/httpx/_client.py
@@ -35,7 +35,7 @@ def build_request(
         self,
         method: Method | str,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ) -> Request:
         return Request(
@@ -49,7 +49,7 @@ def request(
         self,
         method: Method | str,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ) -> Response:
         request = self.build_request(method, url, headers=headers, content=content)
@@ -61,7 +61,7 @@ def stream(
         self,
         method: Method | str,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ) -> Response:
         request = self.build_request(method, url, headers=headers, content=content)
@@ -70,14 +70,14 @@ def stream(
     def get(
         self,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
     ):
         return self.request("GET", url, headers=headers)
 
     def post(
         self,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ):
         return self.request("POST", url, headers=headers, content=content)
@@ -85,7 +85,7 @@ def post(
     def put(
         self,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ):
         return self.request("PUT", url, headers=headers, content=content)
@@ -93,7 +93,7 @@ def put(
     def patch(
         self,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ):
         return self.request("PATCH", url, headers=headers, content=content)
@@ -101,7 +101,7 @@ def patch(
     def delete(
         self,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
     ):
         return self.request("DELETE", url, headers=headers)
 
diff --git a/src/httpx/_headers.py b/src/httpx/_headers.py
index dade805..857754f 100644
--- a/src/httpx/_headers.py
+++ b/src/httpx/_headers.py
@@ -169,6 +169,12 @@ def copy_update(self, update: "Headers" | typing.Mapping[str, str] | None) -> "H
 
         return Headers(h)
 
+    def as_byte_pairs(self) -> list[tuple[bytes, bytes]]:
+        return [
+            (k.encode('ascii'), v.encode('ascii'))
+            for k, v in self.items()
+        ]
+
     def __getitem__(self, key: str) -> str:
         match = key.lower()
         for k, v in self._dict.items():
diff --git a/src/httpx/_pool.py b/src/httpx/_pool.py
index f537be8..8959159 100644
--- a/src/httpx/_pool.py
+++ b/src/httpx/_pool.py
@@ -185,7 +185,7 @@ def request(
         self,
         method: Method | str,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ) -> Response:
         url = self._origin.join(url)
@@ -198,7 +198,7 @@ def stream(
         self,
         method: Method | str,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ) -> Response:
         url = self._origin.join(url)
@@ -211,10 +211,7 @@ def _send_head(self, request: Request) -> None:
         target = request.url.target.encode('ascii')
         protocol = b'HTTP/1.1'
         self._parser.send_method_line(method, target, protocol)
-        headers = [
-            (k.encode('ascii'), v.encode('ascii'))
-            for k, v in request.headers.items()
-        ]
+        headers = request.headers.as_byte_pairs()
         self._parser.send_headers(headers)
 
     def _send_body(self, request: Request) -> None:
diff --git a/src/httpx/_quickstart.py b/src/httpx/_quickstart.py
index 1a97530..fe81a8d 100644
--- a/src/httpx/_quickstart.py
+++ b/src/httpx/_quickstart.py
@@ -12,14 +12,14 @@
 
 def get(
     url: URL | str,
-    headers: Headers | typing.Mapping[str, str] | None = None,
+    headers: Headers | dict[str, str] | None = None,
 ):
     with Client() as client:
         return client.request("GET", url=url, headers=headers)
 
 def post(
     url: URL | str,
-    headers: Headers | typing.Mapping[str, str] | None = None,
+    headers: Headers | dict[str, str] | None = None,
     content: Content | Stream | bytes | None = None,
 ):
     with Client() as client:
@@ -27,7 +27,7 @@ def post(
 
 def put(
     url: URL | str,
-    headers: Headers | typing.Mapping[str, str] | None = None,
+    headers: Headers | dict[str, str] | None = None,
     content: Content | Stream | bytes | None = None,
 ):
     with Client() as client:
@@ -35,7 +35,7 @@ def put(
 
 def patch(
     url: URL | str,
-    headers: Headers | typing.Mapping[str, str] | None = None,
+    headers: Headers | dict[str, str] | None = None,
     content: Content | Stream | bytes | None = None,
 ):
     with Client() as client:
@@ -43,7 +43,7 @@ def patch(
 
 def delete(
     url: URL | str,
-    headers: Headers | typing.Mapping[str, str] | None = None,
+    headers: Headers | dict[str, str] | None = None,
 ):
     with Client() as client:
         return client.request("DELETE", url=url, headers=headers)
diff --git a/src/httpx/_request.py b/src/httpx/_request.py
index 3cf030c..4e7d2b3 100644
--- a/src/httpx/_request.py
+++ b/src/httpx/_request.py
@@ -6,7 +6,7 @@
 from ._headers import Headers
 from ._urls import URL
 
-__all__ = ["Request"]
+__all__ = ["Method", "Request"]
 
 
 class Method:
@@ -35,7 +35,7 @@ def __init__(
         self,
         method: Method | str,
         url: URL | str,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ):
         self.method = Method(method) if not isinstance(method, Method) else method
diff --git a/src/httpx/_response.py b/src/httpx/_response.py
index 0dc43ff..4f4fb13 100644
--- a/src/httpx/_response.py
+++ b/src/httpx/_response.py
@@ -7,84 +7,137 @@
 
 __all__ = ["Response"]
 
-# We're using the same set as stdlib `http.HTTPStatus` here...
-#
-# https://github.com/python/cpython/blob/main/Lib/http/__init__.py
-_codes = {
-    100: "Continue",
-    101: "Switching Protocols",
-    102: "Processing",
-    103: "Early Hints",
-    200: "OK",
-    201: "Created",
-    202: "Accepted",
-    203: "Non-Authoritative Information",
-    204: "No Content",
-    205: "Reset Content",
-    206: "Partial Content",
-    207: "Multi-Status",
-    208: "Already Reported",
-    226: "IM Used",
-    300: "Multiple Choices",
-    301: "Moved Permanently",
-    302: "Found",
-    303: "See Other",
-    304: "Not Modified",
-    305: "Use Proxy",
-    307: "Temporary Redirect",
-    308: "Permanent Redirect",
-    400: "Bad Request",
-    401: "Unauthorized",
-    402: "Payment Required",
-    403: "Forbidden",
-    404: "Not Found",
-    405: "Method Not Allowed",
-    406: "Not Acceptable",
-    407: "Proxy Authentication Required",
-    408: "Request Timeout",
-    409: "Conflict",
-    410: "Gone",
-    411: "Length Required",
-    412: "Precondition Failed",
-    413: "Content Too Large",
-    414: "URI Too Long",
-    415: "Unsupported Media Type",
-    416: "Range Not Satisfiable",
-    417: "Expectation Failed",
-    418: "I'm a Teapot",
-    421: "Misdirected Request",
-    422: "Unprocessable Content",
-    423: "Locked",
-    424: "Failed Dependency",
-    425: "Too Early",
-    426: "Upgrade Required",
-    428: "Precondition Required",
-    429: "Too Many Requests",
-    431: "Request Header Fields Too Large",
-    451: "Unavailable For Legal Reasons",
-    500: "Internal Server Error",
-    501: "Not Implemented",
-    502: "Bad Gateway",
-    503: "Service Unavailable",
-    504: "Gateway Timeout",
-    505: "HTTP Version Not Supported",
-    506: "Variant Also Negotiates",
-    507: "Insufficient Storage",
-    508: "Loop Detected",
-    510: "Not Extended",
-    511: "Network Authentication Required",
-}
+
+class StatusCode:
+    # We're using the same set as stdlib `http.HTTPStatus` here...
+    #
+    # https://github.com/python/cpython/blob/main/Lib/http/__init__.py
+    _codes = {
+        100: "Continue",
+        101: "Switching Protocols",
+        102: "Processing",
+        103: "Early Hints",
+        200: "OK",
+        201: "Created",
+        202: "Accepted",
+        203: "Non-Authoritative Information",
+        204: "No Content",
+        205: "Reset Content",
+        206: "Partial Content",
+        207: "Multi-Status",
+        208: "Already Reported",
+        226: "IM Used",
+        300: "Multiple Choices",
+        301: "Moved Permanently",
+        302: "Found",
+        303: "See Other",
+        304: "Not Modified",
+        305: "Use Proxy",
+        307: "Temporary Redirect",
+        308: "Permanent Redirect",
+        400: "Bad Request",
+        401: "Unauthorized",
+        402: "Payment Required",
+        403: "Forbidden",
+        404: "Not Found",
+        405: "Method Not Allowed",
+        406: "Not Acceptable",
+        407: "Proxy Authentication Required",
+        408: "Request Timeout",
+        409: "Conflict",
+        410: "Gone",
+        411: "Length Required",
+        412: "Precondition Failed",
+        413: "Content Too Large",
+        414: "URI Too Long",
+        415: "Unsupported Media Type",
+        416: "Range Not Satisfiable",
+        417: "Expectation Failed",
+        418: "I'm a Teapot",
+        421: "Misdirected Request",
+        422: "Unprocessable Content",
+        423: "Locked",
+        424: "Failed Dependency",
+        425: "Too Early",
+        426: "Upgrade Required",
+        428: "Precondition Required",
+        429: "Too Many Requests",
+        431: "Request Header Fields Too Large",
+        451: "Unavailable For Legal Reasons",
+        500: "Internal Server Error",
+        501: "Not Implemented",
+        502: "Bad Gateway",
+        503: "Service Unavailable",
+        504: "Gateway Timeout",
+        505: "HTTP Version Not Supported",
+        506: "Variant Also Negotiates",
+        507: "Insufficient Storage",
+        508: "Loop Detected",
+        510: "Not Extended",
+        511: "Network Authentication Required",
+    }
+
+    def __init__(self, status_code: int):
+        if status_code < 100 or status_code > 999:
+            raise ValueError("Invalid status code {status_code!r}")
+        self.value = status_code
+        self.reason_phrase = self._codes.get(status_code, "Unknown Status Code")
+
+    def is_1xx_informational(self) -> bool:
+        """
+        Returns `True` for 1xx status codes, `False` otherwise.
+        """
+        return 100 <= int(self) <= 199
+
+    def is_2xx_success(self) -> bool:
+        """
+        Returns `True` for 2xx status codes, `False` otherwise.
+        """
+        return 200 <= int(self) <= 299
+
+    def is_3xx_redirect(self) -> bool:
+        """
+        Returns `True` for 3xx status codes, `False` otherwise.
+        """
+        return 300 <= int(self) <= 399
+
+    def is_4xx_client_error(self) -> bool:
+        """
+        Returns `True` for 4xx status codes, `False` otherwise.
+        """
+        return 400 <= int(self) <= 499
+
+    def is_5xx_server_error(self) -> bool:
+        """
+        Returns `True` for 5xx status codes, `False` otherwise.
+        """
+        return 500 <= int(self) <= 599
+
+    def as_tuple(self) -> tuple[int, bytes]:
+        return (self.value, self.reason_phrase.encode('ascii'))
+
+    def __eq__(self, other) -> bool:
+        return int(self) == int(other)
+
+    def __int__(self) -> int:
+        return self.value
+
+    def __str__(self) -> str:
+        return f"{self.value} {self.reason_phrase}"
+
+    def __repr__(self) -> str:
+        return f"<StatusCode [{self.value} {self.reason_phrase}]>"
 
 
 class Response:
     def __init__(
         self,
-        status_code: int,
+        status_code: StatusCode | int,
         *,
-        headers: Headers | typing.Mapping[str, str] | None = None,
+        headers: Headers | dict[str, str] | None = None,
         content: Content | Stream | bytes | None = None,
     ):
-        self.status_code = status_code
+        self.status_code = StatusCode(status_code) if not isinstance(status_code, StatusCode) else status_code
         self.headers = Headers(headers) if not isinstance(headers, Headers) else headers
         self.stream: Stream = ByteStream(b"")
 
@@ -106,17 +159,13 @@ def __init__(
         # All 1xx (informational), 204 (no content), and 304 (not modified) responses
         # MUST NOT include a message-body. All other responses do include a
         # message-body, although it MAY be of zero length.
-        if status_code >= 200 and status_code != 204 and status_code != 304:
+        if not(self.status_code.is_1xx_informational() or self.status_code == 204 or self.status_code == 304):
             content_length: int | None = self.stream.size
             if content_length is None:
                 self.headers = self.headers.copy_set("Transfer-Encoding", "chunked")
             else:
                 self.headers = self.headers.copy_set("Content-Length", str(content_length))
 
-    @property
-    def reason_phrase(self):
-        return _codes.get(self.status_code, "Unknown Status Code")
-
     @property
     def body(self) -> bytes:
         if not hasattr(self, '_body'):
@@ -155,4 +204,4 @@ def __exit__(self,
         self.close()
 
     def __repr__(self):
-        return f"<Response [{self.status_code} {self.reason_phrase}]>"
+        return f"<Response [{int(self.status_code)} {self.status_code.reason_phrase}]>"
diff --git a/src/httpx/_server.py b/src/httpx/_server.py
index 31bec5d..4f1ca3a 100644
--- a/src/httpx/_server.py
+++ b/src/httpx/_server.py
@@ -37,7 +37,7 @@ def handle_requests(self):
                 with Request(method, url, headers=headers, content=stream) as request:
                     try:
                         response = self._endpoint(request)
-                        status_line = f"{request.method} {request.url.target} [{response.status_code} {response.reason_phrase}]"
+                        status_line = f"{request.method} {request.url.target} [{response.status_code} {response.status_code.reason_phrase}]"
                         logger.info(status_line)
                     except Exception:
                         logger.error("Internal Server Error", exc_info=True)
@@ -72,13 +72,9 @@ def _recv_body(self):
     # Return the response...
     def _send_head(self, response: Response):
         protocol = b"HTTP/1.1"
-        status = response.status_code
-        reason = response.reason_phrase.encode('ascii')
+        status, reason = response.status_code.as_tuple()
         self._parser.send_status_line(protocol, status, reason)
-        headers = [
-            (k.encode('ascii'), v.encode('ascii'))
-            for k, v in response.headers.items()
-        ]
+        headers = response.headers.as_byte_pairs()
         self._parser.send_headers(headers)
 
     def _send_body(self, response: Response):