diff --git a/lib/openai/client.rb b/lib/openai/client.rb
index 02db6417..2bfddd02 100644
--- a/lib/openai/client.rb
+++ b/lib/openai/client.rb
@@ -77,14 +77,14 @@ class Client < OpenAI::Transport::BaseClient
 
     # Creates and returns a new client for interacting with the API.
     #
-    # @param base_url [String, nil] Override the default base URL for the API, e.g., `"https://api.example.com/v2/"`
-    #
     # @param api_key [String, nil] Defaults to `ENV["OPENAI_API_KEY"]`
     #
     # @param organization [String, nil] Defaults to `ENV["OPENAI_ORG_ID"]`
     #
     # @param project [String, nil] Defaults to `ENV["OPENAI_PROJECT_ID"]`
     #
+    # @param base_url [String, nil] Override the default base URL for the API, e.g., `"https://api.example.com/v2/"`
+    #
     # @param max_retries [Integer] Max number of retries to attempt after a failed retryable request.
     #
     # @param timeout [Float]
@@ -93,10 +93,10 @@ class Client < OpenAI::Transport::BaseClient
     #
     # @param max_retry_delay [Float]
     def initialize(
-      base_url: nil,
       api_key: ENV["OPENAI_API_KEY"],
       organization: ENV["OPENAI_ORG_ID"],
       project: ENV["OPENAI_PROJECT_ID"],
+      base_url: nil,
       max_retries: DEFAULT_MAX_RETRIES,
       timeout: DEFAULT_TIMEOUT_IN_SECONDS,
       initial_retry_delay: DEFAULT_INITIAL_RETRY_DELAY,
@@ -105,7 +105,7 @@ def initialize(
       base_url ||= "https://api.openai.com/v1"
 
       if api_key.nil?
-        raise ArgumentError.new("api_key is required")
+        raise ArgumentError.new("api_key is required, and can be set via environ: \"OPENAI_API_KEY\"")
       end
 
       headers = {
diff --git a/rbi/lib/openai/client.rbi b/rbi/lib/openai/client.rbi
index 5f320546..41d82819 100644
--- a/rbi/lib/openai/client.rbi
+++ b/rbi/lib/openai/client.rbi
@@ -69,10 +69,10 @@ module OpenAI
     # Creates and returns a new client for interacting with the API.
     sig do
       params(
-        base_url: T.nilable(String),
         api_key: T.nilable(String),
         organization: T.nilable(String),
         project: T.nilable(String),
+        base_url: T.nilable(String),
         max_retries: Integer,
         timeout: Float,
         initial_retry_delay: Float,
@@ -81,14 +81,14 @@ module OpenAI
         .returns(T.attached_class)
     end
     def self.new(
-      # Override the default base URL for the API, e.g., `"https://api.example.com/v2/"`
-      base_url: nil,
       # Defaults to `ENV["OPENAI_API_KEY"]`
       api_key: ENV["OPENAI_API_KEY"],
       # Defaults to `ENV["OPENAI_ORG_ID"]`
       organization: ENV["OPENAI_ORG_ID"],
       # Defaults to `ENV["OPENAI_PROJECT_ID"]`
       project: ENV["OPENAI_PROJECT_ID"],
+      # Override the default base URL for the API, e.g., `"https://api.example.com/v2/"`
+      base_url: nil,
       # Max number of retries to attempt after a failed retryable request.
       max_retries: DEFAULT_MAX_RETRIES,
       timeout: DEFAULT_TIMEOUT_IN_SECONDS,
diff --git a/sig/openai/client.rbs b/sig/openai/client.rbs
index a7a4533d..6b95a137 100644
--- a/sig/openai/client.rbs
+++ b/sig/openai/client.rbs
@@ -45,10 +45,10 @@ module OpenAI
     private def auth_headers: -> ::Hash[String, String]
 
     def initialize: (
-      ?base_url: String?,
       ?api_key: String?,
       ?organization: String?,
       ?project: String?,
+      ?base_url: String?,
       ?max_retries: Integer,
       ?timeout: Float,
       ?initial_retry_delay: Float,