diff --git a/stdlib/socket/0/basic_socket.rbs b/stdlib/socket/0/basic_socket.rbs
index a69132467b..63552bd49c 100644
--- a/stdlib/socket/0/basic_socket.rbs
+++ b/stdlib/socket/0/basic_socket.rbs
@@ -237,7 +237,7 @@ class BasicSocket < IO
   #     onoff, linger = optval.unpack "ii"
   #     onoff = onoff == 0 ? false : true
   #
-  def getsockopt: (Symbol | Integer, Symbol | Integer) -> (Integer | boolish | String)
+  def getsockopt: (interned | Integer level, interned | Integer optname) -> Socket::Option
 
   # <!--
   #   rdoc-file=ext/socket/basicsocket.c
@@ -544,7 +544,8 @@ class BasicSocket < IO
   #              IPAddr.new(Socket::INADDR_ANY, Socket::AF_INET).hton
   #     sock.setsockopt(Socket::IPPROTO_IP, Socket::IP_ADD_MEMBERSHIP, optval)
   #
-  def setsockopt: (*Symbol | Integer, boolish | Integer | String) -> void
+  def setsockopt: (Socket::Option socketoption) -> void
+                | (interned | Integer level, interned | Integer optname, boolish | Integer | String optval) -> void
 
   # <!--
   #   rdoc-file=ext/socket/basicsocket.c
diff --git a/stdlib/socket/0/socket.rbs b/stdlib/socket/0/socket.rbs
index 627e730e48..69504ad868 100644
--- a/stdlib/socket/0/socket.rbs
+++ b/stdlib/socket/0/socket.rbs
@@ -504,6 +504,73 @@ class Socket < BasicSocket
               | [T] (String host, Integer port, ?String local_host, ?Integer local_port, ?resolv_timeout: Time::_Timeout, ?connect_timeout: Time::_Timeout) { (instance) -> T } -> T
               | [T] (String host, Integer port, ?String local_host, ?Integer local_port, ?open_timeout: Time::_Timeout) { (instance) -> T } -> T
 
+  # <!--
+  #   rdoc-file=ext/socket/socket.c
+  #   - Socket.tcp_fast_fallback -> true or false
+  # -->
+  # Returns whether Happy Eyeballs Version 2 ([RFC
+  # 8305](https://datatracker.ietf.org/doc/html/rfc8305)), which is provided
+  # starting from Ruby 3.4 when using TCPSocket.new and Socket.tcp, is enabled or
+  # disabled.
+  #
+  # If true, it is enabled for TCPSocket.new and Socket.tcp. (Note: Happy Eyeballs
+  # Version 2 is not provided when using TCPSocket.new on Windows.)
+  #
+  # If false, Happy Eyeballs Version 2 is disabled.
+  #
+  # For details on Happy Eyeballs Version 2, see
+  # [Socket.tcp_fast_fallback=](rdoc-ref:Socket.tcp_fast_fallback=).
+  #
+  def self.tcp_fast_fallback: () -> bool
+
+  # <!--
+  #   rdoc-file=ext/socket/socket.c
+  #   - Socket.tcp_fast_fallback= -> true or false
+  # -->
+  # Enable or disable Happy Eyeballs Version 2 ([RFC
+  # 8305](https://datatracker.ietf.org/doc/html/rfc8305)) globally, which is
+  # provided starting from Ruby 3.4 when using TCPSocket.new and Socket.tcp.
+  #
+  # When set to true, the feature is enabled for both <code>TCPSocket.new</code>
+  # and <code>Socket.tcp</code>. (Note: This feature is not available when using
+  # TCPSocket.new on Windows.)
+  #
+  # When set to false, the behavior reverts to that of Ruby 3.3 or earlier.
+  #
+  # The default value is true if no value is explicitly set by calling this
+  # method. However, when the environment variable RUBY_TCP_NO_FAST_FALLBACK=1 is
+  # set, the default is false.
+  #
+  # To control the setting on a per-method basis, use the fast_fallback keyword
+  # argument for each method.
+  #
+  # ### Happy Eyeballs Version 2
+  # Happy Eyeballs Version 2 ([RFC
+  # 8305](https://datatracker.ietf.org/doc/html/rfc8305)) is an algorithm designed
+  # to improve client socket connectivity.
+  #  It aims for more reliable and efficient connections by performing hostname
+  # resolution and connection attempts in parallel, instead of serially.
+  #
+  # Starting from Ruby 3.4, this method operates as follows with this algorithm:
+  #
+  # 1.  Start resolving both IPv6 and IPv4 addresses concurrently.
+  # 2.  Start connecting to the one of the addresses that are obtained first.
+  #     If IPv4 addresses are obtained first, the method waits 50 ms for IPv6 name
+  #     resolution to prioritize IPv6 connections.
+  # 3.  After starting a connection attempt, wait 250 ms for the connection to be
+  #     established.
+  #      If no connection is established within this time, a new connection is
+  #     started every 250 ms
+  #      until a connection is  established or there are no more candidate
+  #     addresses.
+  #      (Although RFC 8305 strictly specifies sorting addresses,
+  #      this method only alternates between IPv6 / IPv4 addresses due to the
+  #     performance concerns)
+  # 4.  Once a connection is established, all remaining connection attempts are
+  #     canceled.
+  #
+  def self.tcp_fast_fallback=: (bool value) -> bool
+
   # <!--
   #   rdoc-file=ext/socket/lib/socket.rb
   #   - tcp_server_loop(host=nil, port) { |socket, client_addrinfo| ... }
@@ -4156,3 +4223,250 @@ class Socket::AncillaryData
   #
   def initialize: (interned | Integer family, interned | Integer cmsg_level, interned | Integer cmsg_data, String cmsg_data) -> untyped
 end
+
+# <!-- rdoc-file=ext/socket/option.c -->
+# Socket::Option represents a socket option used by BasicSocket#getsockopt and
+# BasicSocket#setsockopt.  A socket option contains the socket #family, protocol
+# #level, option name #optname and option value #data.
+#
+class Socket::Option
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - Socket::Option.new(family, level, optname, data) => sockopt
+  # -->
+  # Returns a new Socket::Option object.
+  #
+  #     sockopt = Socket::Option.new(:INET, :SOCKET, :KEEPALIVE, [1].pack("i"))
+  #     p sockopt #=> #<Socket::Option: INET SOCKET KEEPALIVE 1>
+  #
+  def initialize: (interned | Integer family, interned | Integer level, interned | Integer optname, String data) -> void
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - Socket::Option.bool(family, level, optname, bool) => sockopt
+  # -->
+  # Creates a new Socket::Option object which contains boolean as data. Actually 0
+  # or 1 as int is used.
+  #
+  #     require 'socket'
+  #
+  #     p Socket::Option.bool(:INET, :SOCKET, :KEEPALIVE, true)
+  #     #=> #<Socket::Option: INET SOCKET KEEPALIVE 1>
+  #
+  #     p Socket::Option.bool(:INET, :SOCKET, :KEEPALIVE, false)
+  #     #=> #<Socket::Option: AF_INET SOCKET KEEPALIVE 0>
+  #
+  def self.bool: (interned | Integer family, interned | Integer level, interned | Integer optname, boolish bool) -> instance
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - Socket::Option.byte(family, level, optname, integer) => sockopt
+  # -->
+  # Creates a new Socket::Option object which contains a byte as data.
+  #
+  #     p Socket::Option.byte(:INET, :SOCKET, :KEEPALIVE, 1)
+  #     #=> #<Socket::Option: INET SOCKET KEEPALIVE 1>
+  #
+  def self.byte: (interned | Integer family, interned | Integer level, interned | Integer optname, Integer integer) -> instance
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - Socket::Option.int(family, level, optname, integer) => sockopt
+  # -->
+  # Creates a new Socket::Option object which contains an int as data.
+  #
+  # The size and endian is dependent on the platform.
+  #
+  #     p Socket::Option.int(:INET, :SOCKET, :KEEPALIVE, 1)
+  #     #=> #<Socket::Option: INET SOCKET KEEPALIVE 1>
+  #
+  def self.int: (interned | Integer family, interned | Integer level, interned | Integer optname, Integer integer) -> instance
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - Socket::Option.ipv4_multicast_loop(integer) => sockopt
+  # -->
+  # Creates a new Socket::Option object for IP_MULTICAST_LOOP.
+  #
+  # The size is dependent on the platform.
+  #
+  #     sockopt = Socket::Option.int(:INET, :IPPROTO_IP, :IP_MULTICAST_LOOP, 1)
+  #     p sockopt.int => 1
+  #
+  #     p Socket::Option.ipv4_multicast_loop(10)
+  #     #=> #<Socket::Option: INET IP MULTICAST_LOOP 10>
+  #
+  def self.ipv4_multicast_loop: (Integer integer) -> instance
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - Socket::Option.ipv4_multicast_ttl(integer) => sockopt
+  # -->
+  # Creates a new Socket::Option object for IP_MULTICAST_TTL.
+  #
+  # The size is dependent on the platform.
+  #
+  #     p Socket::Option.ipv4_multicast_ttl(10)
+  #     #=> #<Socket::Option: INET IP MULTICAST_TTL 10>
+  #
+  def self.ipv4_multicast_ttl: (Integer integer) -> instance
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - Socket::Option.linger(onoff, secs) => sockopt
+  # -->
+  # Creates a new Socket::Option object for SOL_SOCKET/SO_LINGER.
+  #
+  # *onoff* should be an integer or a boolean.
+  #
+  # *secs* should be the number of seconds.
+  #
+  #     p Socket::Option.linger(true, 10)
+  #     #=> #<Socket::Option: UNSPEC SOCKET LINGER on 10sec>
+  #
+  def self.linger: (boolish | Integer onoff, Integer secs) -> instance
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - sockopt.bool => true or false
+  # -->
+  # Returns the data in *sockopt* as an boolean value.
+  #
+  #     sockopt = Socket::Option.int(:INET, :SOCKET, :KEEPALIVE, 1)
+  #     p sockopt.bool => true
+  #
+  def bool: () -> bool
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - sockopt.byte => integer
+  # -->
+  # Returns the data in *sockopt* as an byte.
+  #
+  #     sockopt = Socket::Option.byte(:INET, :SOCKET, :KEEPALIVE, 1)
+  #     p sockopt.byte => 1
+  #
+  def byte: () -> Integer
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - sockopt.data => string
+  #   - sockopt.to_s => string
+  # -->
+  # returns the socket option data as a string.
+  #
+  #     p Socket::Option.new(:INET6, :IPV6, :RECVPKTINFO, [1].pack("i!")).data
+  #     #=> "\x01\x00\x00\x00"
+  #
+  def data: () -> String
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - sockopt.family => integer
+  # -->
+  # returns the socket family as an integer.
+  #
+  #     p Socket::Option.new(:INET6, :IPV6, :RECVPKTINFO, [1].pack("i!")).family
+  #     #=> 10
+  #
+  def family: () -> Integer
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - sockopt.inspect => string
+  # -->
+  # Returns a string which shows sockopt in human-readable form.
+  #
+  #     p Socket::Option.new(:INET, :SOCKET, :KEEPALIVE, [1].pack("i")).inspect
+  #     #=> "#<Socket::Option: INET SOCKET KEEPALIVE 1>"
+  #
+  def inspect: () -> String
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - sockopt.int => integer
+  # -->
+  # Returns the data in *sockopt* as an int.
+  #
+  # The size and endian is dependent on the platform.
+  #
+  #     sockopt = Socket::Option.int(:INET, :SOCKET, :KEEPALIVE, 1)
+  #     p sockopt.int => 1
+  #
+  def int: () -> Integer
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - sockopt.ipv4_multicast_loop => integer
+  # -->
+  # Returns the ipv4_multicast_loop data in *sockopt* as an integer.
+  #
+  #     sockopt = Socket::Option.ipv4_multicast_loop(10)
+  #     p sockopt.ipv4_multicast_loop => 10
+  #
+  def ipv4_multicast_loop: () -> Integer
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - sockopt.ipv4_multicast_ttl => integer
+  # -->
+  # Returns the ipv4_multicast_ttl data in *sockopt* as an integer.
+  #
+  #     sockopt = Socket::Option.ipv4_multicast_ttl(10)
+  #     p sockopt.ipv4_multicast_ttl => 10
+  #
+  def ipv4_multicast_ttl: () -> Integer
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - sockopt.level => integer
+  # -->
+  # returns the socket level as an integer.
+  #
+  #     p Socket::Option.new(:INET6, :IPV6, :RECVPKTINFO, [1].pack("i!")).level
+  #     #=> 41
+  #
+  def level: () -> Integer
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - sockopt.linger => [bool, seconds]
+  # -->
+  # Returns the linger data in *sockopt* as a pair of boolean and integer.
+  #
+  #     sockopt = Socket::Option.linger(true, 10)
+  #     p sockopt.linger => [true, 10]
+  #
+  def linger: () -> [ bool, Integer ]
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - sockopt.optname => integer
+  # -->
+  # returns the socket option name as an integer.
+  #
+  #     p Socket::Option.new(:INET6, :IPV6, :RECVPKTINFO, [1].pack("i!")).optname
+  #     #=> 2
+  #
+  def optname: () -> Integer
+
+  # <!-- rdoc-file=ext/socket/option.c -->
+  # returns the socket option data as a string.
+  #
+  #     p Socket::Option.new(:INET6, :IPV6, :RECVPKTINFO, [1].pack("i!")).data
+  #     #=> "\x01\x00\x00\x00"
+  #
+  alias to_s data
+
+  # <!--
+  #   rdoc-file=ext/socket/option.c
+  #   - sockopt.unpack(template) => array
+  # -->
+  # Calls String#unpack on sockopt.data.
+  #
+  #     sockopt = Socket::Option.new(:INET, :SOCKET, :KEEPALIVE, [1].pack("i"))
+  #     p sockopt.unpack("i")      #=> [1]
+  #     p sockopt.data.unpack("i") #=> [1]
+  #
+  def unpack: (String template) -> Array[untyped]
+end
diff --git a/stdlib/socket/0/socket_error.rbs b/stdlib/socket/0/socket_error.rbs
index 02095c7feb..466e575c27 100644
--- a/stdlib/socket/0/socket_error.rbs
+++ b/stdlib/socket/0/socket_error.rbs
@@ -3,3 +3,27 @@
 #
 class SocketError < StandardError
 end
+
+# <!-- rdoc-file=ext/socket/init.c -->
+# Socket::ResolutionError is the error class for hostname resolution.
+#
+class Socket::ResolutionError < SocketError
+  # <!--
+  #   rdoc-file=ext/socket/init.c
+  #   - error_code     -> integer
+  # -->
+  # Returns the raw error code indicating the cause of the hostname resolution
+  # failure.
+  #
+  #     begin
+  #       Addrinfo.getaddrinfo("ruby-lang.org", nil)
+  #     rescue Socket::ResolutionError => e
+  #       if e.error_code == Socket::EAI_AGAIN
+  #         puts "Temporary failure in name resolution."
+  #       end
+  #     end
+  #
+  # Note that error codes depend on the operating system.
+  #
+  def error_code: () -> Integer
+end
diff --git a/test/stdlib/socket/BasicSocket_sockopt_test.rb b/test/stdlib/socket/BasicSocket_sockopt_test.rb
new file mode 100644
index 0000000000..8e886a1b88
--- /dev/null
+++ b/test/stdlib/socket/BasicSocket_sockopt_test.rb
@@ -0,0 +1,44 @@
+require_relative "../test_helper"
+
+require "socket"
+
+class BasicSocketSockoptTest < Test::Unit::TestCase
+  include TestHelper
+
+  library "socket"
+  testing "::BasicSocket"
+
+  def test_getsockopt
+    Socket.open(:INET, :STREAM) do |socket|
+      assert_send_type(
+        "(::Symbol, ::Symbol) -> ::Socket::Option",
+        socket, :getsockopt, :SOCKET, :KEEPALIVE
+      )
+      assert_send_type(
+        "(::Integer, ::Integer) -> ::Socket::Option",
+        socket, :getsockopt, Socket::SOL_SOCKET, Socket::SO_KEEPALIVE
+      )
+    end
+  end
+
+  def test_setsockopt
+    Socket.open(:INET, :STREAM) do |socket|
+      assert_send_type(
+        "(::Socket::Option) -> void",
+        socket, :setsockopt, Socket::Option.bool(:INET, :SOCKET, :KEEPALIVE, true)
+      )
+      assert_send_type(
+        "(::Symbol, ::Symbol, bool) -> void",
+        socket, :setsockopt, :SOCKET, :KEEPALIVE, true
+      )
+      assert_send_type(
+        "(::Symbol, ::Symbol, ::Integer) -> void",
+        socket, :setsockopt, :SOCKET, :KEEPALIVE, 1
+      )
+      assert_send_type(
+        "(::Integer, ::Integer, ::String) -> void",
+        socket, :setsockopt, Socket::SOL_SOCKET, Socket::SO_KEEPALIVE, [1].pack("i")
+      )
+    end
+  end
+end
diff --git a/test/stdlib/socket/SocketOption_test.rb b/test/stdlib/socket/SocketOption_test.rb
new file mode 100644
index 0000000000..b821e98b06
--- /dev/null
+++ b/test/stdlib/socket/SocketOption_test.rb
@@ -0,0 +1,130 @@
+require_relative "../test_helper"
+
+require "socket"
+
+class SocketOptionSingletonTest < Test::Unit::TestCase
+  include TestHelper
+
+  library "socket"
+  testing "singleton(::Socket::Option)"
+
+  def test_new
+    assert_send_type(
+      "(::Symbol, ::Symbol, ::Symbol, ::String) -> ::Socket::Option",
+      Socket::Option, :new, :INET, :SOCKET, :KEEPALIVE, [1].pack("i")
+    )
+    assert_send_type(
+      "(::String, ::Integer, ::Integer, ::String) -> ::Socket::Option",
+      Socket::Option, :new, "INET", Socket::SOL_SOCKET, Socket::SO_KEEPALIVE, [1].pack("i")
+    )
+  end
+
+  def test_bool
+    assert_send_type(
+      "(::Symbol, ::Symbol, ::Symbol, bool) -> ::Socket::Option",
+      Socket::Option, :bool, :INET, :SOCKET, :KEEPALIVE, true
+    )
+  end
+
+  def test_byte
+    assert_send_type(
+      "(::Symbol, ::Symbol, ::Symbol, ::Integer) -> ::Socket::Option",
+      Socket::Option, :byte, :INET, :IP, :TTL, 3
+    )
+  end
+
+  def test_int
+    assert_send_type(
+      "(::Symbol, ::Symbol, ::Symbol, ::Integer) -> ::Socket::Option",
+      Socket::Option, :int, :INET, :SOCKET, :KEEPALIVE, 1
+    )
+  end
+
+  def test_ipv4_multicast_loop
+    assert_send_type(
+      "(::Integer) -> ::Socket::Option",
+      Socket::Option, :ipv4_multicast_loop, 1
+    )
+  end
+
+  def test_ipv4_multicast_ttl
+    assert_send_type(
+      "(::Integer) -> ::Socket::Option",
+      Socket::Option, :ipv4_multicast_ttl, 1
+    )
+  end
+
+  def test_linger
+    assert_send_type(
+      "(bool, ::Integer) -> ::Socket::Option",
+      Socket::Option, :linger, true, 10
+    )
+    assert_send_type(
+      "(::Integer, ::Integer) -> ::Socket::Option",
+      Socket::Option, :linger, 1, 10
+    )
+  end
+end
+
+class SocketOptionTest < Test::Unit::TestCase
+  include TestHelper
+
+  library "socket"
+  testing "::Socket::Option"
+
+  def keepalive
+    Socket::Option.new(:INET, :SOCKET, :KEEPALIVE, [1].pack("i"))
+  end
+
+  def test_bool
+    assert_send_type "() -> bool", keepalive, :bool
+  end
+
+  def test_byte
+    assert_send_type "() -> ::Integer", Socket::Option.byte(:INET, :IP, :TTL, 3), :byte
+  end
+
+  def test_data
+    assert_send_type "() -> ::String", keepalive, :data
+  end
+
+  def test_to_s
+    assert_send_type "() -> ::String", keepalive, :to_s
+  end
+
+  def test_family
+    assert_send_type "() -> ::Integer", keepalive, :family
+  end
+
+  def test_inspect
+    assert_send_type "() -> ::String", keepalive, :inspect
+  end
+
+  def test_int
+    assert_send_type "() -> ::Integer", keepalive, :int
+  end
+
+  def test_ipv4_multicast_loop
+    assert_send_type "() -> ::Integer", Socket::Option.ipv4_multicast_loop(1), :ipv4_multicast_loop
+  end
+
+  def test_ipv4_multicast_ttl
+    assert_send_type "() -> ::Integer", Socket::Option.ipv4_multicast_ttl(1), :ipv4_multicast_ttl
+  end
+
+  def test_level
+    assert_send_type "() -> ::Integer", keepalive, :level
+  end
+
+  def test_linger
+    assert_send_type "() -> [bool, ::Integer]", Socket::Option.linger(true, 10), :linger
+  end
+
+  def test_optname
+    assert_send_type "() -> ::Integer", keepalive, :optname
+  end
+
+  def test_unpack
+    assert_send_type "(::String) -> ::Array[untyped]", keepalive, :unpack, "i"
+  end
+end
diff --git a/test/stdlib/socket/SocketResolutionError_test.rb b/test/stdlib/socket/SocketResolutionError_test.rb
new file mode 100644
index 0000000000..4aa2ccebba
--- /dev/null
+++ b/test/stdlib/socket/SocketResolutionError_test.rb
@@ -0,0 +1,23 @@
+require_relative "../test_helper"
+
+require "socket"
+
+class SocketResolutionErrorTest < Test::Unit::TestCase
+  include TestHelper
+
+  library "socket"
+  testing "::Socket::ResolutionError"
+
+  def resolution_error
+    Addrinfo.getaddrinfo("nonexistent.invalid", nil)
+  rescue Socket::ResolutionError => error
+    error
+  end
+
+  def test_error_code
+    assert_send_type(
+      "() -> ::Integer",
+      resolution_error, :error_code
+    )
+  end
+end
diff --git a/test/stdlib/socket/Socket_test.rb b/test/stdlib/socket/Socket_test.rb
index f024c89456..2c103ddac3 100644
--- a/test/stdlib/socket/Socket_test.rb
+++ b/test/stdlib/socket/Socket_test.rb
@@ -66,6 +66,23 @@ def test_tcp
       )
     end
   end
+
+  def test_tcp_fast_fallback
+    assert_send_type(
+      "() -> bool",
+      Socket, :tcp_fast_fallback
+    )
+  end
+
+  def test_tcp_fast_fallback=
+    original = Socket.tcp_fast_fallback
+    assert_send_type(
+      "(bool) -> bool",
+      Socket, :tcp_fast_fallback=, false
+    )
+  ensure
+    Socket.tcp_fast_fallback = original
+  end
 end
 
 class SocketInstanceTest < Test::Unit::TestCase