diff --git a/lib/grpc/client/adapter.ex b/lib/grpc/client/adapter.ex
index 6cec2b6f..f623be62 100644
--- a/lib/grpc/client/adapter.ex
+++ b/lib/grpc/client/adapter.ex
@@ -9,15 +9,21 @@ defmodule GRPC.Client.Adapter do
   @typedoc "Determines if the headers have finished being read."
   @type fin :: :fin | :nofin
 
-  @callback connect(Channel.t(), map()) :: {:ok, Channel.t()} | {:error, any()}
+  @callback connect(channel :: Channel.t(), opts :: keyword()) ::
+              {:ok, Channel.t()} | {:error, any()}
 
-  @callback disconnect(Channel.t()) :: {:ok, Channel.t()} | {:error, any()}
+  @callback disconnect(channel :: Channel.t()) :: {:ok, Channel.t()} | {:error, any()}
 
-  @callback send_request(Stream.t(), binary(), map()) :: Stream.t()
+  @callback send_request(stream :: Stream.t(), contents :: binary(), opts :: keyword()) ::
+              Stream.t()
 
-  @callback recv_headers(map(), map(), map()) ::
+  @callback recv_headers(stream :: map(), headers :: map(), opts :: keyword()) ::
               {:ok, %{String.t() => String.t()}, fin()} | {:error, GRPC.RPCError.t()}
 
-  @callback recv_data_or_trailers(map(), map(), map()) ::
+  @callback recv_data_or_trailers(
+              stream :: map(),
+              trailers_or_metadata :: map(),
+              opts :: keyword()
+            ) ::
               {:data, binary()} | {:trailers, binary()} | {:error, GRPC.RPCError.t()}
 end
diff --git a/lib/grpc/client/adapters/gun.ex b/lib/grpc/client/adapters/gun.ex
index 1dd6de38..088abeed 100644
--- a/lib/grpc/client/adapters/gun.ex
+++ b/lib/grpc/client/adapters/gun.ex
@@ -11,9 +11,15 @@ defmodule GRPC.Client.Adapters.Gun do
   @max_retries 100
 
   @impl true
-  def connect(channel, opts \\ %{})
-  def connect(%{scheme: "https"} = channel, opts), do: connect_securely(channel, opts)
-  def connect(channel, opts), do: connect_insecurely(channel, opts)
+  def connect(channel, opts) when is_list(opts) do
+    # handle opts as a map due to :gun.open
+    opts = Map.new(opts)
+
+    case channel do
+      %{scheme: "https"} -> connect_securely(channel, opts)
+      _ -> connect_insecurely(channel, opts)
+    end
+  end
 
   defp connect_securely(%{cred: %{ssl: ssl}} = channel, opts) do
     transport_opts = Map.get(opts, :transport_opts) || []
diff --git a/lib/grpc/message.ex b/lib/grpc/message.ex
index 2ba3b227..0f4d782b 100644
--- a/lib/grpc/message.ex
+++ b/lib/grpc/message.ex
@@ -39,7 +39,7 @@ defmodule GRPC.Message do
       {:error, "Encoded message is too large (9 bytes)"}
 
   """
-  @spec to_data(iodata, keyword() | map()) ::
+  @spec to_data(iodata, keyword()) ::
           {:ok, iodata, non_neg_integer} | {:error, String.t()}
   def to_data(message, opts \\ []) do
     compressor = opts[:compressor]
diff --git a/lib/grpc/server/adapter.ex b/lib/grpc/server/adapter.ex
index f2f30093..9884ac9f 100644
--- a/lib/grpc/server/adapter.ex
+++ b/lib/grpc/server/adapter.ex
@@ -11,12 +11,17 @@ defmodule GRPC.Server.Adapter do
           pending_reader: nil
         }
 
-  @callback start(atom(), %{String.t() => [module()]}, non_neg_integer(), Keyword.t()) ::
+  @callback start(
+              atom(),
+              %{String.t() => [module()]},
+              port :: non_neg_integer(),
+              opts :: keyword()
+            ) ::
               {atom(), any(), non_neg_integer()}
 
   @callback stop(atom(), %{String.t() => [module()]}) :: :ok | {:error, :not_found}
 
-  @callback send_reply(state(), binary(), Keyword.t()) :: any()
+  @callback send_reply(state, content :: binary(), opts :: keyword()) :: any()
 
-  @callback send_headers(state(), map()) :: any()
+  @callback send_headers(state, headers :: map()) :: any()
 end
diff --git a/lib/grpc/server/adapters/cowboy/handler.ex b/lib/grpc/server/adapters/cowboy/handler.ex
index 433b6fda..ec87568c 100644
--- a/lib/grpc/server/adapters/cowboy/handler.ex
+++ b/lib/grpc/server/adapters/cowboy/handler.ex
@@ -11,7 +11,10 @@ defmodule GRPC.Server.Adapters.Cowboy.Handler do
   @adapter GRPC.Server.Adapters.Cowboy
   @default_trailers HTTP2.server_trailers()
 
-  @spec init(map(), {atom(), %{String.t() => [module()]}, map()}) :: {:cowboy_loop, map(), map()}
+  @spec init(
+          map(),
+          state :: {endpoint :: atom(), servers :: %{String.t() => [module()]}, opts :: keyword()}
+        ) :: {:cowboy_loop, map(), map()}
   def init(req, {endpoint, servers, opts} = state) do
     path = :cowboy_req.path(req)
 
@@ -472,8 +475,8 @@ defmodule GRPC.Server.Adapters.Cowboy.Handler do
   end
 
   defp async_read_body(req, opts) do
-    length = Map.get(opts, :length, 8_000_000)
-    period = Map.get(opts, :period, 15000)
+    length = opts[:length] || 8_000_000
+    period = opts[:period] || 15000
     ref = make_ref()
 
     :cowboy_req.cast({:read_body, self(), ref, length, period}, req)
diff --git a/lib/grpc/stub.ex b/lib/grpc/stub.ex
index eb5c7f09..848c39c0 100644
--- a/lib/grpc/stub.ex
+++ b/lib/grpc/stub.ex
@@ -125,7 +125,7 @@ defmodule GRPC.Stub do
     * `:accepted_compressors` - tell servers accepted compressors, this can be used without `:compressor`
     * `:headers` - headers to attach to each request
   """
-  @spec connect(String.t(), Keyword.t()) :: {:ok, Channel.t()} | {:error, any()}
+  @spec connect(String.t(), keyword()) :: {:ok, Channel.t()} | {:error, any()}
   def connect(addr, opts \\ []) when is_binary(addr) and is_list(opts) do
     {host, port} =
       case String.split(addr, ":") do
@@ -136,7 +136,7 @@ defmodule GRPC.Stub do
     connect(host, port, opts)
   end
 
-  @spec connect(String.t(), binary() | non_neg_integer(), Keyword.t()) ::
+  @spec connect(String.t(), binary() | non_neg_integer(), keyword()) ::
           {:ok, Channel.t()} | {:error, any()}
   def connect(host, port, opts) when is_binary(port) do
     connect(host, String.to_integer(port), opts)
@@ -162,6 +162,12 @@ defmodule GRPC.Stub do
         accepted_compressors
       end
 
+    adapter_opts = opts[:adapter_opts] || []
+
+    unless is_list(adapter_opts) do
+      raise ArgumentError, ":adapter_opts must be a keyword list if present"
+    end
+
     %Channel{
       host: host,
       port: port,
@@ -174,7 +180,7 @@ defmodule GRPC.Stub do
       accepted_compressors: accepted_compressors,
       headers: headers
     }
-    |> adapter.connect(opts[:adapter_opts] || %{})
+    |> adapter.connect(adapter_opts)
   end
 
   def retry_timeout(curr) when curr < 11 do
@@ -231,7 +237,7 @@ defmodule GRPC.Stub do
       with the last elem being a map of headers `%{headers: headers, trailers: trailers}`(unary) or
       `%{headers: headers}`(server streaming)
   """
-  @spec call(atom(), tuple(), GRPC.Client.Stream.t(), struct() | nil, Keyword.t()) :: rpc_return
+  @spec call(atom(), tuple(), GRPC.Client.Stream.t(), struct() | nil, keyword()) :: rpc_return
   def call(_service_mod, rpc, %{channel: channel} = stream, request, opts) do
     {_, {req_mod, req_stream}, {res_mod, response_stream}} = rpc
 
@@ -239,13 +245,17 @@ defmodule GRPC.Stub do
 
     opts =
       if req_stream || response_stream do
-        parse_req_opts([{:timeout, :infinity} | opts])
+        opts
+        |> parse_req_opts()
+        |> Keyword.put_new(:timeout, :infinity)
       else
-        parse_req_opts([{:timeout, @default_timeout} | opts])
+        opts
+        |> parse_req_opts()
+        |> Keyword.put_new(:timeout, @default_timeout)
       end
 
-    compressor = Map.get(opts, :compressor, channel.compressor)
-    accepted_compressors = Map.get(opts, :accepted_compressors, [])
+    compressor = Keyword.get(opts, :compressor, channel.compressor)
+    accepted_compressors = Keyword.get(opts, :accepted_compressors, [])
 
     accepted_compressors =
       if compressor do
@@ -256,8 +266,8 @@ defmodule GRPC.Stub do
 
     stream = %{
       stream
-      | codec: Map.get(opts, :codec, channel.codec),
-        compressor: Map.get(opts, :compressor, channel.compressor),
+      | codec: Keyword.get(opts, :codec, channel.codec),
+        compressor: Keyword.get(opts, :compressor, channel.compressor),
         accepted_compressors: accepted_compressors
     }
 
@@ -272,7 +282,7 @@ defmodule GRPC.Stub do
        ) do
     last = fn %{codec: codec, compressor: compressor} = s, _ ->
       message = codec.encode(request)
-      opts = Map.put(opts, :compressor, compressor)
+      opts = Keyword.put(opts, :compressor, compressor)
 
       s
       |> channel.adapter.send_request(message, opts)
@@ -319,7 +329,7 @@ defmodule GRPC.Stub do
     * `:end_stream` - indicates it's the last one request, then the stream will be in
       half_closed state. Default is false.
   """
-  @spec send_request(GRPC.Client.Stream.t(), struct, Keyword.t()) :: GRPC.Client.Stream.t()
+  @spec send_request(GRPC.Client.Stream.t(), struct, keyword()) :: GRPC.Client.Stream.t()
   def send_request(%{__interface__: interface} = stream, request, opts \\ []) do
     interface[:send_request].(stream, request, opts)
   end
@@ -376,7 +386,7 @@ defmodule GRPC.Stub do
     * `:deadline` - when the request is timeout, will override timeout
     * `:return_headers` - when true, headers will be returned.
   """
-  @spec recv(GRPC.Client.Stream.t(), Keyword.t() | map()) ::
+  @spec recv(GRPC.Client.Stream.t(), keyword()) ::
           {:ok, struct()}
           | {:ok, struct(), map()}
           | {:ok, Enumerable.t()}
@@ -391,7 +401,7 @@ defmodule GRPC.Stub do
   def recv(%{__interface__: interface} = stream, opts) do
     opts =
       if is_list(opts) do
-        parse_recv_opts(opts)
+        parse_recv_opts(Keyword.put_new(opts, :timeout, @default_timeout))
       else
         opts
       end
@@ -588,72 +598,39 @@ defmodule GRPC.Stub do
     end
   end
 
-  defp parse_req_opts(list) when is_list(list) do
-    parse_req_opts(list, %{})
-  end
-
-  defp parse_req_opts([{:timeout, timeout} | t], acc) do
-    parse_req_opts(t, Map.put(acc, :timeout, timeout))
-  end
-
-  defp parse_req_opts([{:deadline, deadline} | t], acc) do
-    parse_req_opts(t, Map.put(acc, :timeout, GRPC.TimeUtils.to_relative(deadline)))
-  end
-
-  defp parse_req_opts([{:compressor, compressor} | t], acc) do
-    parse_req_opts(t, Map.put(acc, :compressor, compressor))
-  end
-
-  defp parse_req_opts([{:accepted_compressors, compressors} | t], acc) do
-    parse_req_opts(t, Map.put(acc, :accepted_compressors, compressors))
-  end
-
-  defp parse_req_opts([{:grpc_encoding, grpc_encoding} | t], acc) do
-    parse_req_opts(t, Map.put(acc, :grpc_encoding, grpc_encoding))
-  end
-
-  defp parse_req_opts([{:metadata, metadata} | t], acc) do
-    parse_req_opts(t, Map.put(acc, :metadata, metadata))
-  end
-
-  defp parse_req_opts([{:content_type, content_type} | t], acc) do
-    Logger.warn(":content_type has been deprecated, please use :codec")
-    parse_req_opts(t, Map.put(acc, :content_type, content_type))
-  end
-
-  defp parse_req_opts([{:codec, codec} | t], acc) do
-    parse_req_opts(t, Map.put(acc, :codec, codec))
-  end
-
-  defp parse_req_opts([{:return_headers, return_headers} | t], acc) do
-    parse_req_opts(t, Map.put(acc, :return_headers, return_headers))
-  end
-
-  defp parse_req_opts([{key, _} | _], _) do
-    raise ArgumentError, "option #{inspect(key)} is not supported"
+  @valid_req_opts [
+    :timeout,
+    :deadline,
+    :compressor,
+    :accepted_compressors,
+    :grpc_encoding,
+    :metadata,
+    :codec,
+    :return_headers
+  ]
+  defp parse_req_opts(opts) when is_list(opts) do
+    Enum.map(opts, fn
+      {:deadline, deadline} ->
+        {:timeout, GRPC.TimeUtils.to_relative(deadline)}
+
+      {key, value} when key in @valid_req_opts ->
+        {key, value}
+
+      {key, _} ->
+        raise ArgumentError, "option #{inspect(key)} is not supported"
+    end)
   end
 
-  defp parse_req_opts(_, acc), do: acc
-
   defp parse_recv_opts(list) when is_list(list) do
-    parse_recv_opts(list, %{timeout: @default_timeout})
-  end
-
-  defp parse_recv_opts([{:timeout, timeout} | t], acc) do
-    parse_recv_opts(t, Map.put(acc, :timeout, timeout))
-  end
-
-  defp parse_recv_opts([{:deadline, deadline} | t], acc) do
-    parse_recv_opts(t, Map.put(acc, :deadline, GRPC.TimeUtils.to_relative(deadline)))
-  end
+    Enum.map(list, fn
+      {:deadline, deadline} ->
+        {:deadline, GRPC.TimeUtils.to_relative(deadline)}
 
-  defp parse_recv_opts([{:return_headers, return_headers} | t], acc) do
-    parse_recv_opts(t, Map.put(acc, :return_headers, return_headers))
-  end
+      {key, _} when key not in @valid_req_opts ->
+        raise ArgumentError, "option #{inspect(key)} is not supported"
 
-  defp parse_recv_opts([{key, _} | _], _) do
-    raise ArgumentError, "option #{inspect(key)} is not supported"
+      kv ->
+        kv
+    end)
   end
-
-  defp parse_recv_opts(_, acc), do: acc
 end
diff --git a/lib/grpc/transport/http2.ex b/lib/grpc/transport/http2.ex
index 189830fc..353a0ba4 100644
--- a/lib/grpc/transport/http2.ex
+++ b/lib/grpc/transport/http2.ex
@@ -23,8 +23,8 @@ defmodule GRPC.Transport.HTTP2 do
   @doc """
   Now we may not need this because gun already handles the pseudo headers.
   """
-  @spec client_headers(GRPC.Client.Stream.t(), map) :: [{String.t(), String.t()}]
-  def client_headers(%{channel: channel, path: path} = s, opts \\ %{}) do
+  @spec client_headers(GRPC.Client.Stream.t(), keyword()) :: [{String.t(), String.t()}]
+  def client_headers(%{channel: channel, path: path} = s, opts \\ []) do
     [
       {":method", "POST"},
       {":scheme", channel.scheme},
@@ -33,8 +33,10 @@ defmodule GRPC.Transport.HTTP2 do
     ] ++ client_headers_without_reserved(s, opts)
   end
 
-  @spec client_headers_without_reserved(GRPC.Client.Stream.t(), map) :: [{String.t(), String.t()}]
-  def client_headers_without_reserved(%{codec: codec} = stream, opts \\ %{}) do
+  @spec client_headers_without_reserved(GRPC.Client.Stream.t(), keyword()) :: [
+          {String.t(), String.t()}
+        ]
+  def client_headers_without_reserved(%{codec: codec} = stream, opts \\ []) do
     [
       # It seems only gRPC implemenations only support "application/grpc", so we support :content_type now.
       {"content-type", content_type(opts[:content_type], codec)},
diff --git a/test/grpc/adapter/gun_test.exs b/test/grpc/adapter/gun_test.exs
index 04840eb5..b3d089e0 100644
--- a/test/grpc/adapter/gun_test.exs
+++ b/test/grpc/adapter/gun_test.exs
@@ -26,7 +26,7 @@ defmodule GRPC.Client.Adapters.GunTest do
     test "connects insecurely (default options)", %{port: port, credential: credential} do
       channel = build(:channel, port: port, host: "localhost", cred: credential)
 
-      assert {:ok, result} = Gun.connect(channel)
+      assert {:ok, result} = Gun.connect(channel, [])
 
       assert %{channel | adapter_payload: %{conn_pid: result.adapter_payload.conn_pid}} == result
     end
@@ -35,12 +35,12 @@ defmodule GRPC.Client.Adapters.GunTest do
       channel = build(:channel, port: port, host: "localhost", cred: credential)
 
       # Ensure that it works
-      assert {:ok, result} = Gun.connect(channel, %{transport_opts: [ip: :loopback]})
+      assert {:ok, result} = Gun.connect(channel, transport_opts: [ip: :loopback])
       assert %{channel | adapter_payload: %{conn_pid: result.adapter_payload.conn_pid}} == result
 
       # Ensure that changing one of the options breaks things
       assert {:error, {:down, :badarg}} ==
-               Gun.connect(channel, %{transport_opts: [ip: "256.0.0.0"]})
+               Gun.connect(channel, transport_opts: [ip: "256.0.0.0"])
     end
 
     test "connects securely (default options)", %{port: port, credential: credential} do
@@ -52,7 +52,7 @@ defmodule GRPC.Client.Adapters.GunTest do
           cred: credential
         )
 
-      assert {:ok, result} = Gun.connect(channel, %{tls_opts: channel.cred.ssl})
+      assert {:ok, result} = Gun.connect(channel, tls_opts: channel.cred.ssl)
 
       assert %{channel | adapter_payload: %{conn_pid: result.adapter_payload.conn_pid}} == result
     end
@@ -68,20 +68,20 @@ defmodule GRPC.Client.Adapters.GunTest do
 
       # Ensure that it works
       assert {:ok, result} =
-               Gun.connect(channel, %{
+               Gun.connect(channel,
                  transport_opts: [certfile: credential.ssl[:certfile], ip: :loopback]
-               })
+               )
 
       assert %{channel | adapter_payload: %{conn_pid: result.adapter_payload.conn_pid}} == result
 
       # Ensure that changing one of the options breaks things
       assert {:error, :timeout} ==
-               Gun.connect(channel, %{
+               Gun.connect(channel,
                  transport_opts: [
                    certfile: credential.ssl[:certfile] <> "invalidsuffix",
                    ip: :loopback
                  ]
-               })
+               )
     end
   end
 end
diff --git a/test/grpc/integration/connection_test.exs b/test/grpc/integration/connection_test.exs
index bdd25cfc..fe68d005 100644
--- a/test/grpc/integration/connection_test.exs
+++ b/test/grpc/integration/connection_test.exs
@@ -9,7 +9,7 @@ defmodule GRPC.Integration.ConnectionTest do
     server = FeatureServer
     {:ok, _, port} = GRPC.Server.start(server, 0)
     point = Routeguide.Point.new(latitude: 409_146_138, longitude: -746_188_906)
-    {:ok, channel} = GRPC.Stub.connect("localhost:#{port}", adapter_opts: %{retry_timeout: 10})
+    {:ok, channel} = GRPC.Stub.connect("localhost:#{port}", adapter_opts: [retry_timeout: 10])
     assert {:ok, _} = channel |> Routeguide.RouteGuide.Stub.get_feature(point)
     :ok = GRPC.Server.stop(server)
     {:ok, _, _} = reconnect_server(server, port)
@@ -23,7 +23,7 @@ defmodule GRPC.Integration.ConnectionTest do
     File.rm(socket_path)
 
     {:ok, _, _} = GRPC.Server.start(server, 0, ip: {:local, socket_path})
-    {:ok, channel} = GRPC.Stub.connect(socket_path, adapter_opts: %{retry_timeout: 10})
+    {:ok, channel} = GRPC.Stub.connect(socket_path, adapter_opts: [retry_timeout: 10])
 
     point = Routeguide.Point.new(latitude: 409_146_138, longitude: -746_188_906)
     assert {:ok, _} = channel |> Routeguide.RouteGuide.Stub.get_feature(point)