diff --git a/lib/travel_time.rb b/lib/travel_time.rb
index d9acc8e..9288e16 100644
--- a/lib/travel_time.rb
+++ b/lib/travel_time.rb
@@ -1,11 +1,6 @@
 # frozen_string_literal: true
 
 require 'dry/configurable'
-require 'travel_time/client'
-require 'travel_time/error'
-require 'travel_time/response'
-require 'travel_time/version'
-require 'utils'
 
 # Main TravelTime module
 module TravelTime
@@ -20,3 +15,9 @@ module TravelTime
   setting :enable_logging, default: false
   setting :raise_on_failure, default: false
 end
+
+require 'travel_time/client'
+require 'travel_time/error'
+require 'travel_time/response'
+require 'travel_time/version'
+require 'utils'
diff --git a/lib/travel_time/client.rb b/lib/travel_time/client.rb
index cc6f7db..ac8ea82 100644
--- a/lib/travel_time/client.rb
+++ b/lib/travel_time/client.rb
@@ -9,10 +9,19 @@
 module TravelTime
   # The Client class provides the main interface to interact with the TravelTime API
   class Client # rubocop:disable Metrics/ClassLength
+    include Dry::Configurable
     extend Limiter::Mixin
 
     API_BASE_URL = 'https://api.traveltimeapp.com/v4/'
 
+    TravelTime.settings.each do |s|
+      if s.default.nil?
+        setting s.name
+      else
+        setting s.name, default: s.default
+      end
+    end
+
     attr_reader :connection, :proto_connection
 
     def initialize(rate_limit = nil)
@@ -26,23 +35,41 @@ def initialize(rate_limit = nil)
       end
     end
 
+    # Override configure to reinitialize connections after config changes
+    def configure
+      super.tap do
+        init_connection
+        init_proto_connection
+      end
+    end
+
+    def effective_config
+      has_instance_config = TravelTime.settings.any? do |s|
+        value = config.public_send(s.name)
+        s.default.nil? ? !value.nil? : value != s.default
+      end
+      has_instance_config ? config : TravelTime.config
+    end
+
     def init_connection
+      cfg = effective_config
       @connection = Faraday.new(API_BASE_URL) do |f|
         f.request :json
-        f.response :raise_error if TravelTime.config.raise_on_failure
-        f.response :logger if TravelTime.config.enable_logging
+        f.response :raise_error if cfg.raise_on_failure
+        f.response :logger if cfg.enable_logging
         f.response :json
-        f.use TravelTime::Middleware::Authentication
-        f.adapter TravelTime.config.http_adapter || Faraday.default_adapter
+        f.use TravelTime::Middleware::Authentication, config: cfg
+        f.adapter cfg.http_adapter || Faraday.default_adapter
       end
     end
 
     def init_proto_connection
+      cfg = effective_config
       @proto_connection = Faraday.new do |f|
-        f.use TravelTime::Middleware::ProtoMiddleware
-        f.response :raise_error if TravelTime.config.raise_on_failure
-        f.response :logger if TravelTime.config.enable_logging
-        f.adapter TravelTime.config.http_adapter || Faraday.default_adapter
+        f.use TravelTime::Middleware::ProtoMiddleware, config: cfg
+        f.response :raise_error if cfg.raise_on_failure
+        f.response :logger if cfg.enable_logging
+        f.adapter cfg.http_adapter || Faraday.default_adapter
       end
     end
 
diff --git a/lib/travel_time/middleware/authentication.rb b/lib/travel_time/middleware/authentication.rb
index 1c5cf15..585cc01 100644
--- a/lib/travel_time/middleware/authentication.rb
+++ b/lib/travel_time/middleware/authentication.rb
@@ -11,9 +11,14 @@ class Authentication < Faraday::Middleware
       API_KEY_HEADER = 'X-Api-Key'
       USER_AGENT = 'User-Agent'
 
+      def initialize(app, options = {})
+        super(app)
+        @config = options[:config] || TravelTime.config
+      end
+
       def on_request(env)
-        env.request_headers[APP_ID_HEADER] = TravelTime.config.application_id
-        env.request_headers[API_KEY_HEADER] = TravelTime.config.api_key
+        env.request_headers[APP_ID_HEADER] = @config.application_id
+        env.request_headers[API_KEY_HEADER] = @config.api_key
         env.request_headers[USER_AGENT] = "Travel Time Ruby SDK #{TravelTime::VERSION}"
       end
     end
diff --git a/lib/travel_time/middleware/proto.rb b/lib/travel_time/middleware/proto.rb
index c524630..94daca2 100644
--- a/lib/travel_time/middleware/proto.rb
+++ b/lib/travel_time/middleware/proto.rb
@@ -8,9 +8,14 @@ module Middleware
     # The Proto middleware is responsible for setting the basic auth headers for proto requests
     # on each request. These are automatically taken from the `TravelTime.config`.
     class ProtoMiddleware < Faraday::Middleware
+      def initialize(app, options = {})
+        super(app)
+        @config = options[:config] || TravelTime.config
+      end
+
       def on_request(env)
         env.request_headers['Authorization'] =
-          "Basic #{Base64.encode64("#{TravelTime.config.application_id}:#{TravelTime.config.api_key}")}"
+          "Basic #{Base64.encode64("#{@config.application_id}:#{@config.api_key}")}"
         env.request_headers['Content-Type'] = 'application/octet-stream'
         env.request_headers['Accept'] = 'application/octet-stream'
         env.request_headers['User-Agent'] = 'Travel Time Ruby SDK'
diff --git a/spec/travel_time/client_spec.rb b/spec/travel_time/client_spec.rb
index 97a6753..b077f39 100644
--- a/spec/travel_time/client_spec.rb
+++ b/spec/travel_time/client_spec.rb
@@ -13,6 +13,36 @@
     expect(connection.builder.handlers).to include(TravelTime::Middleware::Authentication)
   end
 
+  describe 'custom credentials' do
+    let(:custom_client) do
+      described_class.new.configure do |config|
+        config.application_id = 'CUSTOM_APP_ID'
+        config.api_key = 'CUSTOM_KEY'
+      end
+    end
+
+    it 'allows setting custom application_id' do
+      expect(custom_client.config.application_id).to eq('CUSTOM_APP_ID')
+    end
+
+    it 'allows setting custom api_key' do
+      expect(custom_client.config.api_key).to eq('CUSTOM_KEY')
+    end
+
+    it 'uses instance config when custom credentials are set' do
+      custom_client = described_class.new.configure do |config|
+        config.application_id = 'CUSTOM_APP_ID'
+        config.api_key = 'CUSTOM_KEY'
+      end
+      expect(custom_client.send(:effective_config)).to eq(custom_client.config)
+    end
+
+    it 'falls back to global config when no custom credentials are set' do
+      default_client = described_class.new
+      expect(default_client.send(:effective_config)).to eq(TravelTime.config)
+    end
+  end
+
   describe 'connection adapter' do
     context 'with default config' do
       let(:expected) { Faraday::Adapter.lookup_middleware(Faraday.default_adapter) }
diff --git a/spec/travel_time/middleware/authentication_spec.rb b/spec/travel_time/middleware/authentication_spec.rb
index 666c783..2cd44d3 100644
--- a/spec/travel_time/middleware/authentication_spec.rb
+++ b/spec/travel_time/middleware/authentication_spec.rb
@@ -6,7 +6,8 @@
       env.request_headers = Faraday::Utils::Headers.new
     end
   end
-  let(:middleware) { described_class.new }
+  let(:app) { instance_double(Faraday::Middleware) }
+  let(:middleware) { described_class.new(app) }
 
   it 'automatically fetches the application_id from the configuration and set it for the request' do
     middleware.on_request(faraday_env)
diff --git a/spec/travel_time/middleware/proto_middleware_spec.rb b/spec/travel_time/middleware/proto_middleware_spec.rb
index 29f24bb..b868b1f 100644
--- a/spec/travel_time/middleware/proto_middleware_spec.rb
+++ b/spec/travel_time/middleware/proto_middleware_spec.rb
@@ -6,7 +6,8 @@
       env.request_headers = Faraday::Utils::Headers.new
     end
   end
-  let(:middleware) { described_class.new }
+  let(:app) { instance_double(Faraday::Middleware) }
+  let(:middleware) { described_class.new(app) }
 
   it 'adds basic auth header' do
     middleware.on_request(faraday_env)