diff --git a/lib/openai/client.ex b/lib/openai/client.ex
index a1c71b8..422ab1e 100644
--- a/lib/openai/client.ex
+++ b/lib/openai/client.ex
@@ -3,7 +3,7 @@ defmodule OpenAI.Client do
   alias OpenAI.{Config, Stream}
   use HTTPoison.Base
 
-  def process_url(url), do: Config.api_url() <> url
+  def process_url(url), do: Config.api_url(url)
 
   def process_response_body(body) do
     try do
@@ -60,12 +60,18 @@ defmodule OpenAI.Client do
     end
   end
 
+  def add_custom_headers(headers, config) do
+    custom_headers = config.custom_headers || Config.custom_headers()
+    headers ++ custom_headers
+  end
+
   def request_headers(config) do
     [
       bearer(config),
       {"Content-type", "application/json"}
     ]
     |> add_organization_header(config)
+    |> add_custom_headers(config)
   end
 
   def bearer(config), do: {"Authorization", "Bearer #{config.api_key || Config.api_key()}"}
@@ -79,6 +85,16 @@ defmodule OpenAI.Client do
   end
 
   def api_post(url, params \\ [], config) do
+    IO.inspect config, label: "API_POST_CONFIG"
+
+    url = case config.api_url do
+      nil ->
+        url
+
+      _ ->
+        config.api_url <> url
+    end
+
     body =
       params
       |> Enum.into(%{})
diff --git a/lib/openai/config.ex b/lib/openai/config.ex
index 86d19b2..787f6d2 100644
--- a/lib/openai/config.ex
+++ b/lib/openai/config.ex
@@ -7,7 +7,8 @@ defmodule OpenAI.Config do
   defstruct api_key: nil,
             organization_key: nil,
             http_options: nil,
-            api_url: nil
+            api_url: nil,
+            custom_headers: nil
 
   use GenServer
 
@@ -16,7 +17,8 @@ defmodule OpenAI.Config do
   @config_keys [
     :api_key,
     :organization_key,
-    :http_options
+    :http_options,
+    :api_url
   ]
 
   def start_link(opts), do: GenServer.start_link(__MODULE__, opts, name: __MODULE__)
@@ -38,9 +40,19 @@ defmodule OpenAI.Config do
   # API Url
   def api_url, do: get_config_value(:api_url, @openai_url)
 
+  def api_url(url) do
+    uri = URI.parse(url)
+    case uri.host do
+      nil -> api_url() <> url
+      _ -> url
+    end
+  end
+
   # HTTP Options
   def http_options, do: get_config_value(:http_options, [])
 
+  def custom_headers, do: get_config_value(:custom_headers, [])
+
   defp get_config_value(key, default \\ nil) do
     value =
       :openai