diff --git a/CHANGES/5275.feature b/CHANGES/5275.feature
new file mode 100644
index 0000000000..e44960a322
--- /dev/null
+++ b/CHANGES/5275.feature
@@ -0,0 +1 @@
+Add final declarations for constants.
diff --git a/aiohttp/client.py b/aiohttp/client.py
index bea1198991..7bb823fb14 100644
--- a/aiohttp/client.py
+++ b/aiohttp/client.py
@@ -30,7 +30,7 @@
 )
 
 from multidict import CIMultiDict, MultiDict, MultiDictProxy, istr
-from typing_extensions import final
+from typing_extensions import Final, final
 from yarl import URL
 
 from . import hdrs, http, payload
@@ -158,7 +158,7 @@ class ClientTimeout:
 
 
 # 5 Minute default read timeout
-DEFAULT_TIMEOUT = ClientTimeout(total=5 * 60)
+DEFAULT_TIMEOUT: Final[ClientTimeout] = ClientTimeout(total=5 * 60)
 
 _RetType = TypeVar("_RetType")
 
diff --git a/aiohttp/client_proto.py b/aiohttp/client_proto.py
index 640d1272cd..c265521ba3 100644
--- a/aiohttp/client_proto.py
+++ b/aiohttp/client_proto.py
@@ -149,7 +149,7 @@ def set_response_params(
         read_until_eof: bool = False,
         auto_decompress: bool = True,
         read_timeout: Optional[float] = None,
-        read_bufsize: int = 2 ** 16
+        read_bufsize: int = 2 ** 16,
     ) -> None:
         self._skip_payload = skip_payload
 
diff --git a/aiohttp/client_ws.py b/aiohttp/client_ws.py
index 4bf5a3754b..f25c4dd072 100644
--- a/aiohttp/client_ws.py
+++ b/aiohttp/client_ws.py
@@ -5,6 +5,7 @@
 from typing import Any, Optional
 
 import async_timeout
+from typing_extensions import Final
 
 from .client_exceptions import ClientError
 from .client_reqrep import ClientResponse
@@ -33,7 +34,9 @@ class ClientWSTimeout:
     ws_close: Optional[float] = None
 
 
-DEFAULT_WS_CLIENT_TIMEOUT = ClientWSTimeout(ws_receive=None, ws_close=10.0)
+DEFAULT_WS_CLIENT_TIMEOUT: Final[ClientWSTimeout] = ClientWSTimeout(
+    ws_receive=None, ws_close=10.0
+)
 
 
 class ClientWebSocketResponse:
diff --git a/aiohttp/formdata.py b/aiohttp/formdata.py
index 12cfda77ce..7eaf122a52 100644
--- a/aiohttp/formdata.py
+++ b/aiohttp/formdata.py
@@ -45,7 +45,7 @@ def add_field(
         *,
         content_type: Optional[str] = None,
         filename: Optional[str] = None,
-        content_transfer_encoding: Optional[str] = None
+        content_transfer_encoding: Optional[str] = None,
     ) -> None:
 
         if isinstance(value, io.IOBase):
diff --git a/aiohttp/hdrs.py b/aiohttp/hdrs.py
index f04a5457f9..d7d8e5000f 100644
--- a/aiohttp/hdrs.py
+++ b/aiohttp/hdrs.py
@@ -2,21 +2,23 @@
 
 # After changing the file content call ./tools/gen.py
 # to regenerate the headers parser
+from typing import Set
 
 from multidict import istr
+from typing_extensions import Final
 
-METH_ANY = "*"
-METH_CONNECT = "CONNECT"
-METH_HEAD = "HEAD"
-METH_GET = "GET"
-METH_DELETE = "DELETE"
-METH_OPTIONS = "OPTIONS"
-METH_PATCH = "PATCH"
-METH_POST = "POST"
-METH_PUT = "PUT"
-METH_TRACE = "TRACE"
+METH_ANY: Final[str] = "*"
+METH_CONNECT: Final[str] = "CONNECT"
+METH_HEAD: Final[str] = "HEAD"
+METH_GET: Final[str] = "GET"
+METH_DELETE: Final[str] = "DELETE"
+METH_OPTIONS: Final[str] = "OPTIONS"
+METH_PATCH: Final[str] = "PATCH"
+METH_POST: Final[str] = "POST"
+METH_PUT: Final[str] = "PUT"
+METH_TRACE: Final[str] = "TRACE"
 
-METH_ALL = {
+METH_ALL: Final[Set[str]] = {
     METH_CONNECT,
     METH_HEAD,
     METH_GET,
@@ -28,81 +30,80 @@
     METH_TRACE,
 }
 
-
-ACCEPT = istr("Accept")
-ACCEPT_CHARSET = istr("Accept-Charset")
-ACCEPT_ENCODING = istr("Accept-Encoding")
-ACCEPT_LANGUAGE = istr("Accept-Language")
-ACCEPT_RANGES = istr("Accept-Ranges")
-ACCESS_CONTROL_MAX_AGE = istr("Access-Control-Max-Age")
-ACCESS_CONTROL_ALLOW_CREDENTIALS = istr("Access-Control-Allow-Credentials")
-ACCESS_CONTROL_ALLOW_HEADERS = istr("Access-Control-Allow-Headers")
-ACCESS_CONTROL_ALLOW_METHODS = istr("Access-Control-Allow-Methods")
-ACCESS_CONTROL_ALLOW_ORIGIN = istr("Access-Control-Allow-Origin")
-ACCESS_CONTROL_EXPOSE_HEADERS = istr("Access-Control-Expose-Headers")
-ACCESS_CONTROL_REQUEST_HEADERS = istr("Access-Control-Request-Headers")
-ACCESS_CONTROL_REQUEST_METHOD = istr("Access-Control-Request-Method")
-AGE = istr("Age")
-ALLOW = istr("Allow")
-AUTHORIZATION = istr("Authorization")
-CACHE_CONTROL = istr("Cache-Control")
-CONNECTION = istr("Connection")
-CONTENT_DISPOSITION = istr("Content-Disposition")
-CONTENT_ENCODING = istr("Content-Encoding")
-CONTENT_LANGUAGE = istr("Content-Language")
-CONTENT_LENGTH = istr("Content-Length")
-CONTENT_LOCATION = istr("Content-Location")
-CONTENT_MD5 = istr("Content-MD5")
-CONTENT_RANGE = istr("Content-Range")
-CONTENT_TRANSFER_ENCODING = istr("Content-Transfer-Encoding")
-CONTENT_TYPE = istr("Content-Type")
-COOKIE = istr("Cookie")
-DATE = istr("Date")
-DESTINATION = istr("Destination")
-DIGEST = istr("Digest")
-ETAG = istr("Etag")
-EXPECT = istr("Expect")
-EXPIRES = istr("Expires")
-FORWARDED = istr("Forwarded")
-FROM = istr("From")
-HOST = istr("Host")
-IF_MATCH = istr("If-Match")
-IF_MODIFIED_SINCE = istr("If-Modified-Since")
-IF_NONE_MATCH = istr("If-None-Match")
-IF_RANGE = istr("If-Range")
-IF_UNMODIFIED_SINCE = istr("If-Unmodified-Since")
-KEEP_ALIVE = istr("Keep-Alive")
-LAST_EVENT_ID = istr("Last-Event-ID")
-LAST_MODIFIED = istr("Last-Modified")
-LINK = istr("Link")
-LOCATION = istr("Location")
-MAX_FORWARDS = istr("Max-Forwards")
-ORIGIN = istr("Origin")
-PRAGMA = istr("Pragma")
-PROXY_AUTHENTICATE = istr("Proxy-Authenticate")
-PROXY_AUTHORIZATION = istr("Proxy-Authorization")
-RANGE = istr("Range")
-REFERER = istr("Referer")
-RETRY_AFTER = istr("Retry-After")
-SEC_WEBSOCKET_ACCEPT = istr("Sec-WebSocket-Accept")
-SEC_WEBSOCKET_VERSION = istr("Sec-WebSocket-Version")
-SEC_WEBSOCKET_PROTOCOL = istr("Sec-WebSocket-Protocol")
-SEC_WEBSOCKET_EXTENSIONS = istr("Sec-WebSocket-Extensions")
-SEC_WEBSOCKET_KEY = istr("Sec-WebSocket-Key")
-SEC_WEBSOCKET_KEY1 = istr("Sec-WebSocket-Key1")
-SERVER = istr("Server")
-SET_COOKIE = istr("Set-Cookie")
-TE = istr("TE")
-TRAILER = istr("Trailer")
-TRANSFER_ENCODING = istr("Transfer-Encoding")
-UPGRADE = istr("Upgrade")
-URI = istr("URI")
-USER_AGENT = istr("User-Agent")
-VARY = istr("Vary")
-VIA = istr("Via")
-WANT_DIGEST = istr("Want-Digest")
-WARNING = istr("Warning")
-WWW_AUTHENTICATE = istr("WWW-Authenticate")
-X_FORWARDED_FOR = istr("X-Forwarded-For")
-X_FORWARDED_HOST = istr("X-Forwarded-Host")
-X_FORWARDED_PROTO = istr("X-Forwarded-Proto")
+ACCEPT: Final[istr] = istr("Accept")
+ACCEPT_CHARSET: Final[istr] = istr("Accept-Charset")
+ACCEPT_ENCODING: Final[istr] = istr("Accept-Encoding")
+ACCEPT_LANGUAGE: Final[istr] = istr("Accept-Language")
+ACCEPT_RANGES: Final[istr] = istr("Accept-Ranges")
+ACCESS_CONTROL_MAX_AGE: Final[istr] = istr("Access-Control-Max-Age")
+ACCESS_CONTROL_ALLOW_CREDENTIALS: Final[istr] = istr("Access-Control-Allow-Credentials")
+ACCESS_CONTROL_ALLOW_HEADERS: Final[istr] = istr("Access-Control-Allow-Headers")
+ACCESS_CONTROL_ALLOW_METHODS: Final[istr] = istr("Access-Control-Allow-Methods")
+ACCESS_CONTROL_ALLOW_ORIGIN: Final[istr] = istr("Access-Control-Allow-Origin")
+ACCESS_CONTROL_EXPOSE_HEADERS: Final[istr] = istr("Access-Control-Expose-Headers")
+ACCESS_CONTROL_REQUEST_HEADERS: Final[istr] = istr("Access-Control-Request-Headers")
+ACCESS_CONTROL_REQUEST_METHOD: Final[istr] = istr("Access-Control-Request-Method")
+AGE: Final[istr] = istr("Age")
+ALLOW: Final[istr] = istr("Allow")
+AUTHORIZATION: Final[istr] = istr("Authorization")
+CACHE_CONTROL: Final[istr] = istr("Cache-Control")
+CONNECTION: Final[istr] = istr("Connection")
+CONTENT_DISPOSITION: Final[istr] = istr("Content-Disposition")
+CONTENT_ENCODING: Final[istr] = istr("Content-Encoding")
+CONTENT_LANGUAGE: Final[istr] = istr("Content-Language")
+CONTENT_LENGTH: Final[istr] = istr("Content-Length")
+CONTENT_LOCATION: Final[istr] = istr("Content-Location")
+CONTENT_MD5: Final[istr] = istr("Content-MD5")
+CONTENT_RANGE: Final[istr] = istr("Content-Range")
+CONTENT_TRANSFER_ENCODING: Final[istr] = istr("Content-Transfer-Encoding")
+CONTENT_TYPE: Final[istr] = istr("Content-Type")
+COOKIE: Final[istr] = istr("Cookie")
+DATE: Final[istr] = istr("Date")
+DESTINATION: Final[istr] = istr("Destination")
+DIGEST: Final[istr] = istr("Digest")
+ETAG: Final[istr] = istr("Etag")
+EXPECT: Final[istr] = istr("Expect")
+EXPIRES: Final[istr] = istr("Expires")
+FORWARDED: Final[istr] = istr("Forwarded")
+FROM: Final[istr] = istr("From")
+HOST: Final[istr] = istr("Host")
+IF_MATCH: Final[istr] = istr("If-Match")
+IF_MODIFIED_SINCE: Final[istr] = istr("If-Modified-Since")
+IF_NONE_MATCH: Final[istr] = istr("If-None-Match")
+IF_RANGE: Final[istr] = istr("If-Range")
+IF_UNMODIFIED_SINCE: Final[istr] = istr("If-Unmodified-Since")
+KEEP_ALIVE: Final[istr] = istr("Keep-Alive")
+LAST_EVENT_ID: Final[istr] = istr("Last-Event-ID")
+LAST_MODIFIED: Final[istr] = istr("Last-Modified")
+LINK: Final[istr] = istr("Link")
+LOCATION: Final[istr] = istr("Location")
+MAX_FORWARDS: Final[istr] = istr("Max-Forwards")
+ORIGIN: Final[istr] = istr("Origin")
+PRAGMA: Final[istr] = istr("Pragma")
+PROXY_AUTHENTICATE: Final[istr] = istr("Proxy-Authenticate")
+PROXY_AUTHORIZATION: Final[istr] = istr("Proxy-Authorization")
+RANGE: Final[istr] = istr("Range")
+REFERER: Final[istr] = istr("Referer")
+RETRY_AFTER: Final[istr] = istr("Retry-After")
+SEC_WEBSOCKET_ACCEPT: Final[istr] = istr("Sec-WebSocket-Accept")
+SEC_WEBSOCKET_VERSION: Final[istr] = istr("Sec-WebSocket-Version")
+SEC_WEBSOCKET_PROTOCOL: Final[istr] = istr("Sec-WebSocket-Protocol")
+SEC_WEBSOCKET_EXTENSIONS: Final[istr] = istr("Sec-WebSocket-Extensions")
+SEC_WEBSOCKET_KEY: Final[istr] = istr("Sec-WebSocket-Key")
+SEC_WEBSOCKET_KEY1: Final[istr] = istr("Sec-WebSocket-Key1")
+SERVER: Final[istr] = istr("Server")
+SET_COOKIE: Final[istr] = istr("Set-Cookie")
+TE: Final[istr] = istr("TE")
+TRAILER: Final[istr] = istr("Trailer")
+TRANSFER_ENCODING: Final[istr] = istr("Transfer-Encoding")
+UPGRADE: Final[istr] = istr("Upgrade")
+URI: Final[istr] = istr("URI")
+USER_AGENT: Final[istr] = istr("User-Agent")
+VARY: Final[istr] = istr("Vary")
+VIA: Final[istr] = istr("Via")
+WANT_DIGEST: Final[istr] = istr("Want-Digest")
+WARNING: Final[istr] = istr("Warning")
+WWW_AUTHENTICATE: Final[istr] = istr("WWW-Authenticate")
+X_FORWARDED_FOR: Final[istr] = istr("X-Forwarded-For")
+X_FORWARDED_HOST: Final[istr] = istr("X-Forwarded-Host")
+X_FORWARDED_PROTO: Final[istr] = istr("X-Forwarded-Proto")
diff --git a/aiohttp/http_parser.py b/aiohttp/http_parser.py
index 2ea0387ce4..8fe60a82c7 100644
--- a/aiohttp/http_parser.py
+++ b/aiohttp/http_parser.py
@@ -6,9 +6,21 @@
 import zlib
 from contextlib import suppress
 from enum import IntEnum
-from typing import Any, Generic, List, Optional, Tuple, Type, TypeVar, Union
+from typing import (
+    Any,
+    Generic,
+    List,
+    Optional,
+    Pattern,
+    Set,
+    Tuple,
+    Type,
+    TypeVar,
+    Union,
+)
 
 from multidict import CIMultiDict, CIMultiDictProxy, istr
+from typing_extensions import Final
 from yarl import URL
 
 from . import hdrs
@@ -44,7 +56,7 @@
     "RawResponseMessage",
 )
 
-ASCIISET = set(string.printable)
+ASCIISET: Final[Set[str]] = set(string.printable)
 
 # See https://tools.ietf.org/html/rfc7230#section-3.1.1
 # and https://tools.ietf.org/html/rfc7230#appendix-B
@@ -53,9 +65,9 @@
 #     tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
 #             "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
 #     token = 1*tchar
-METHRE = re.compile(r"[!#$%&'*+\-.^_`|~0-9A-Za-z]+")
-VERSRE = re.compile(r"HTTP/(\d+).(\d+)")
-HDRRE = re.compile(rb"[\x00-\x1F\x7F()<>@,;:\[\]={} \t\\\\\"]")
+METHRE: Final[Pattern[str]] = re.compile(r"[!#$%&'*+\-.^_`|~0-9A-Za-z]+")
+VERSRE: Final[Pattern[str]] = re.compile(r"HTTP/(\d+).(\d+)")
+HDRRE: Final[Pattern[bytes]] = re.compile(rb"[\x00-\x1F\x7F()<>@,;:\[\]={} \t\\\\\"]")
 
 RawRequestMessage = collections.namedtuple(
     "RawRequestMessage",
diff --git a/aiohttp/http_websocket.py b/aiohttp/http_websocket.py
index d0dee7f451..bff70f0968 100644
--- a/aiohttp/http_websocket.py
+++ b/aiohttp/http_websocket.py
@@ -9,7 +9,9 @@
 import zlib
 from enum import IntEnum
 from struct import Struct
-from typing import Any, Callable, List, Optional, Tuple, Union
+from typing import Any, Callable, List, Optional, Pattern, Set, Tuple, Union
+
+from typing_extensions import Final
 
 from .base_protocol import BaseProtocol
 from .helpers import NO_EXTENSIONS
@@ -44,7 +46,7 @@ class WSCloseCode(IntEnum):
     BAD_GATEWAY = 1014
 
 
-ALLOWED_CLOSE_CODES = {int(i) for i in WSCloseCode}
+ALLOWED_CLOSE_CODES: Final[Set[int]] = {int(i) for i in WSCloseCode}
 
 
 class WSMsgType(IntEnum):
@@ -62,7 +64,7 @@ class WSMsgType(IntEnum):
     ERROR = 0x102
 
 
-WS_KEY = b"258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
+WS_KEY: Final[bytes] = b"258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
 
 
 UNPACK_LEN2 = Struct("!H").unpack_from
@@ -72,8 +74,8 @@ class WSMsgType(IntEnum):
 PACK_LEN2 = Struct("!BBH").pack
 PACK_LEN3 = Struct("!BBQ").pack
 PACK_CLOSE_CODE = Struct("!H").pack
-MSG_SIZE = 2 ** 14
-DEFAULT_LIMIT = 2 ** 16
+MSG_SIZE: Final[int] = 2 ** 14
+DEFAULT_LIMIT: Final[int] = 2 ** 16
 
 
 _WSMessageBase = collections.namedtuple("_WSMessageBase", ["type", "data", "extra"])
@@ -107,11 +109,11 @@ class WSHandshakeError(Exception):
     """WebSocket protocol handshake error."""
 
 
-native_byteorder = sys.byteorder
+native_byteorder: Final[str] = sys.byteorder
 
 
 # Used by _websocket_mask_python
-_XOR_TABLE = [bytes(a ^ b for a in range(256)) for b in range(256)]
+_XOR_TABLE: Final[List[bytes]] = [bytes(a ^ b for a in range(256)) for b in range(256)]
 
 
 def _websocket_mask_python(mask: bytes, data: bytearray) -> None:
@@ -148,10 +150,10 @@ def _websocket_mask_python(mask: bytes, data: bytearray) -> None:
     except ImportError:  # pragma: no cover
         _websocket_mask = _websocket_mask_python
 
-_WS_DEFLATE_TRAILING = bytes([0x00, 0x00, 0xFF, 0xFF])
+_WS_DEFLATE_TRAILING: Final[bytes] = bytes([0x00, 0x00, 0xFF, 0xFF])
 
 
-_WS_EXT_RE = re.compile(
+_WS_EXT_RE: Final[Pattern[str]] = re.compile(
     r"^(?:;\s*(?:"
     r"(server_no_context_takeover)|"
     r"(client_no_context_takeover)|"
@@ -159,7 +161,7 @@ def _websocket_mask_python(mask: bytes, data: bytearray) -> None:
     r"(client_max_window_bits(?:=(\d+))?)))*$"
 )
 
-_WS_EXT_RE_SPLIT = re.compile(r"permessage-deflate([^,]+)?")
+_WS_EXT_RE_SPLIT: Final[Pattern[str]] = re.compile(r"permessage-deflate([^,]+)?")
 
 
 def ws_ext_parse(extstr: Optional[str], isserver: bool = False) -> Tuple[int, bool]:
diff --git a/aiohttp/payload.py b/aiohttp/payload.py
index 0e881e41ea..b3f5f842e4 100644
--- a/aiohttp/payload.py
+++ b/aiohttp/payload.py
@@ -23,6 +23,7 @@
 )
 
 from multidict import CIMultiDict
+from typing_extensions import Final
 
 from . import hdrs
 from .abc import AbstractStreamWriter
@@ -52,7 +53,7 @@
     "AsyncIterablePayload",
 )
 
-TOO_LARGE_BYTES_BODY = 2 ** 20  # 1 MB
+TOO_LARGE_BYTES_BODY: Final[int] = 2 ** 20  # 1 MB
 
 
 if TYPE_CHECKING:  # pragma: no cover
diff --git a/aiohttp/streams.py b/aiohttp/streams.py
index d8182b3d5f..d07b16e61c 100644
--- a/aiohttp/streams.py
+++ b/aiohttp/streams.py
@@ -111,7 +111,7 @@ def __init__(
         limit: int,
         *,
         timer: Optional[BaseTimerContext] = None,
-        loop: asyncio.AbstractEventLoop
+        loop: asyncio.AbstractEventLoop,
     ) -> None:
         self._protocol = protocol
         self._low_water = limit
diff --git a/aiohttp/web.py b/aiohttp/web.py
index eb23dd3ff7..8a5030cc26 100644
--- a/aiohttp/web.py
+++ b/aiohttp/web.py
@@ -6,16 +6,16 @@
 from collections.abc import Iterable
 from importlib import import_module
 from typing import (
-    Any as Any,
-    Awaitable as Awaitable,
-    Callable as Callable,
+    Any,
+    Awaitable,
+    Callable,
     Iterable as TypingIterable,
-    List as List,
-    Optional as Optional,
-    Set as Set,
-    Type as Type,
-    Union as Union,
-    cast as cast,
+    List,
+    Optional,
+    Set,
+    Type,
+    Union,
+    cast,
 )
 
 from .abc import AbstractAccessLogger
diff --git a/aiohttp/web_fileresponse.py b/aiohttp/web_fileresponse.py
index 0737c4f42d..6e475010fc 100644
--- a/aiohttp/web_fileresponse.py
+++ b/aiohttp/web_fileresponse.py
@@ -15,6 +15,8 @@
     cast,
 )
 
+from typing_extensions import Final
+
 from . import hdrs
 from .abc import AbstractStreamWriter
 from .typedefs import LooseHeaders
@@ -35,7 +37,7 @@
 _T_OnChunkSent = Optional[Callable[[bytes], Awaitable[None]]]
 
 
-NOSENDFILE = bool(os.environ.get("AIOHTTP_NOSENDFILE"))
+NOSENDFILE: Final[bool] = bool(os.environ.get("AIOHTTP_NOSENDFILE"))
 
 
 class FileResponse(StreamResponse):
diff --git a/aiohttp/web_middlewares.py b/aiohttp/web_middlewares.py
index b122bd14fe..1c30b93f9f 100644
--- a/aiohttp/web_middlewares.py
+++ b/aiohttp/web_middlewares.py
@@ -50,7 +50,7 @@ def normalize_path_middleware(
     append_slash: bool = True,
     remove_slash: bool = False,
     merge_slashes: bool = True,
-    redirect_class: Type[HTTPMove] = HTTPPermanentRedirect
+    redirect_class: Type[HTTPMove] = HTTPPermanentRedirect,
 ) -> _Middleware:
     """
     Middleware factory which produces a middleware that normalizes
diff --git a/aiohttp/web_request.py b/aiohttp/web_request.py
index b95a5631a8..7493b4ac58 100644
--- a/aiohttp/web_request.py
+++ b/aiohttp/web_request.py
@@ -18,6 +18,7 @@
     Mapping,
     MutableMapping,
     Optional,
+    Pattern,
     Set,
     Tuple,
     Union,
@@ -26,6 +27,7 @@
 from urllib.parse import parse_qsl
 
 from multidict import CIMultiDict, CIMultiDictProxy, MultiDict, MultiDictProxy
+from typing_extensions import Final
 from yarl import URL
 
 from . import hdrs
@@ -75,31 +77,33 @@ class FileField:
     headers: "CIMultiDictProxy[str]"
 
 
-_TCHAR = string.digits + string.ascii_letters + r"!#$%&'*+.^_`|~-"
+_TCHAR: Final[str] = string.digits + string.ascii_letters + r"!#$%&'*+.^_`|~-"
 # '-' at the end to prevent interpretation as range in a char class
 
-_TOKEN = fr"[{_TCHAR}]+"
+_TOKEN: Final[str] = fr"[{_TCHAR}]+"
 
-_QDTEXT = r"[{}]".format(
+_QDTEXT: Final[str] = r"[{}]".format(
     r"".join(chr(c) for c in (0x09, 0x20, 0x21) + tuple(range(0x23, 0x7F)))
 )
 # qdtext includes 0x5C to escape 0x5D ('\]')
 # qdtext excludes obs-text (because obsoleted, and encoding not specified)
 
-_QUOTED_PAIR = r"\\[\t !-~]"
+_QUOTED_PAIR: Final[str] = r"\\[\t !-~]"
 
-_QUOTED_STRING = r'"(?:{quoted_pair}|{qdtext})*"'.format(
+_QUOTED_STRING: Final[str] = r'"(?:{quoted_pair}|{qdtext})*"'.format(
     qdtext=_QDTEXT, quoted_pair=_QUOTED_PAIR
 )
 
-_FORWARDED_PAIR = r"({token})=({token}|{quoted_string})(:\d{{1,4}})?".format(
+_FORWARDED_PAIR: Final[
+    str
+] = r"({token})=({token}|{quoted_string})(:\d{{1,4}})?".format(
     token=_TOKEN, quoted_string=_QUOTED_STRING
 )
 
-_QUOTED_PAIR_REPLACE_RE = re.compile(r"\\([\t !-~])")
+_QUOTED_PAIR_REPLACE_RE: Final[Pattern[str]] = re.compile(r"\\([\t !-~])")
 # same pattern as _QUOTED_PAIR but contains a capture group
 
-_FORWARDED_PAIR_RE = re.compile(_FORWARDED_PAIR)
+_FORWARDED_PAIR_RE: Final[Pattern[str]] = re.compile(_FORWARDED_PAIR)
 
 ############################################################
 # HTTP Request
diff --git a/aiohttp/web_server.py b/aiohttp/web_server.py
index 8fdee1891c..1c9fbf34ca 100644
--- a/aiohttp/web_server.py
+++ b/aiohttp/web_server.py
@@ -19,7 +19,7 @@ def __init__(
         *,
         request_factory: Optional[_RequestFactory] = None,
         debug: Optional[bool] = None,
-        **kwargs: Any
+        **kwargs: Any,
     ) -> None:
         if debug is not None:
             warnings.warn(
diff --git a/aiohttp/web_urldispatcher.py b/aiohttp/web_urldispatcher.py
index 590b376afe..28e9232911 100644
--- a/aiohttp/web_urldispatcher.py
+++ b/aiohttp/web_urldispatcher.py
@@ -29,7 +29,7 @@
     cast,
 )
 
-from typing_extensions import TypedDict
+from typing_extensions import Final, TypedDict
 from yarl import URL, __version__ as yarl_version  # type: ignore
 
 from . import hdrs
@@ -70,11 +70,15 @@
 else:
     BaseDict = dict
 
-YARL_VERSION = tuple(map(int, yarl_version.split(".")[:2]))
+YARL_VERSION: Final[Tuple[int, ...]] = tuple(map(int, yarl_version.split(".")[:2]))
 
-HTTP_METHOD_RE = re.compile(r"^[0-9A-Za-z!#\$%&'\*\+\-\.\^_`\|~]+$")
-ROUTE_RE = re.compile(r"(\{[_a-zA-Z][^{}]*(?:\{[^{}]*\}[^{}]*)*\})")
-PATH_SEP = re.escape("/")
+HTTP_METHOD_RE: Final[Pattern[str]] = re.compile(
+    r"^[0-9A-Za-z!#\$%&'\*\+\-\.\^_`\|~]+$"
+)
+ROUTE_RE: Final[Pattern[str]] = re.compile(
+    r"(\{[_a-zA-Z][^{}]*(?:\{[^{}]*\}[^{}]*)*\})"
+)
+PATH_SEP: Final[str] = re.escape("/")
 
 
 _WebHandler = Callable[[Request], Awaitable[StreamResponse]]
diff --git a/aiohttp/web_ws.py b/aiohttp/web_ws.py
index 6b295e773b..f23313d77b 100644
--- a/aiohttp/web_ws.py
+++ b/aiohttp/web_ws.py
@@ -8,6 +8,7 @@
 
 import async_timeout
 from multidict import CIMultiDict
+from typing_extensions import Final
 
 from . import hdrs
 from .abc import AbstractStreamWriter
@@ -38,7 +39,7 @@
     "WSMsgType",
 )
 
-THRESHOLD_CONNLOST_ACCESS = 5
+THRESHOLD_CONNLOST_ACCESS: Final[int] = 5
 
 
 @dataclasses.dataclass(frozen=True)
diff --git a/requirements/cython.txt b/requirements/cython.txt
index e478589498..2d3627402e 100644
--- a/requirements/cython.txt
+++ b/requirements/cython.txt
@@ -1,2 +1,3 @@
 -r multidict.txt
 cython==0.29.21
+typing_extensions==3.7.4.3  # required for parsing aiohttp/hdrs.py by tools/gen.py