diff --git a/lib/convertkit.rb b/lib/convertkit.rb
index c50757d..dca157b 100644
--- a/lib/convertkit.rb
+++ b/lib/convertkit.rb
@@ -19,8 +19,12 @@
 require 'convertkit/resources/sequence_response'
 require 'convertkit/resources/sequences'
 require 'convertkit/resources/subscriber_response'
+require 'convertkit/resources/subscriber_bulk_add_tag_response'
 require 'convertkit/resources/subscriber_bulk_create_response'
 require 'convertkit/resources/subscriber_bulk_create_failure_response'
+require 'convertkit/resources/subscriber_bulk_remove_tag_response'
+require 'convertkit/resources/subscriber_bulk_tag_failure_response'
+require 'convertkit/resources/subscriber_tag_response'
 require 'convertkit/resources/subscribers'
 require 'convertkit/resources/subscribers_response'
 require 'convertkit/resources/subscription_response'
diff --git a/lib/convertkit/client.rb b/lib/convertkit/client.rb
index 550bcaa..222a0e6 100644
--- a/lib/convertkit/client.rb
+++ b/lib/convertkit/client.rb
@@ -69,4 +69,12 @@ def handle_response(response, raw_response= false)
       end
     end
   end
+
+  # This client behaves like the standard Client, but uses an API Key rather than OAuth access_token.
+  # Certain API resources can only be accessed with an OAuth access_token
+  class DeveloperClient < Client
+    def initialize(api_key)
+      @connection = ConvertKit::Connection.new(API_URL, api_key: api_key)
+    end
+  end
 end
diff --git a/lib/convertkit/connection.rb b/lib/convertkit/connection.rb
index 367e9b0..78cfba2 100644
--- a/lib/convertkit/connection.rb
+++ b/lib/convertkit/connection.rb
@@ -10,8 +10,10 @@ class Connection
     def initialize(url, options = {})
       @url = url
 
-      @connection = Faraday.new(url: @url, headers: {'content-type' => MIME_TYPE }) do |builder|
-        builder.request :authorization, 'Bearer', options[:auth_token] if options[:auth_token]
+      @connection = Faraday.new(url: @url, headers: default_headers(options)) do |builder|
+        if options[:auth_token]
+          builder.request :authorization, 'Bearer', options[:auth_token]
+        end
       end
     end
 
@@ -32,6 +34,12 @@ def initialize(url, options = {})
 
     private
 
+    def default_headers(options)
+      headers = { 'Content-Type' => MIME_TYPE }
+      headers['X-Kit-Api-Key'] = options[:api_key] if options[:api_key]
+      headers
+    end
+
     def process_request(method, params)
       return params if method == :get
       return params if params.empty?
diff --git a/lib/convertkit/resources/subscriber_bulk_add_tag_response.rb b/lib/convertkit/resources/subscriber_bulk_add_tag_response.rb
new file mode 100644
index 0000000..5b6cbd4
--- /dev/null
+++ b/lib/convertkit/resources/subscriber_bulk_add_tag_response.rb
@@ -0,0 +1,17 @@
+module ConvertKit
+  module Resources
+    class SubscriberBulkAddTagResponse
+      attr_accessor :subscribers, :failures
+
+      def initialize(response)
+        @subscribers = response['subscribers'].map do |subscriber|
+          ConvertKit::Resources::TaggedSubscriberResponse.new(subscriber)
+        end
+
+        @failures = response['failures'].map do |failure|
+          ConvertKit::Resources::SubscriberBulkTagFailureResponse.new(failure)
+        end
+      end
+    end
+  end
+end
diff --git a/lib/convertkit/resources/subscriber_bulk_remove_tag_response.rb b/lib/convertkit/resources/subscriber_bulk_remove_tag_response.rb
new file mode 100644
index 0000000..0f8612e
--- /dev/null
+++ b/lib/convertkit/resources/subscriber_bulk_remove_tag_response.rb
@@ -0,0 +1,13 @@
+module ConvertKit
+  module Resources
+    class SubscriberBulkRemoveTagResponse
+      attr_accessor :failures
+
+      def initialize(response)
+        @failures = response['failures'].map do |failure|
+          ConvertKit::Resources::SubscriberBulkTagFailureResponse.new(failure)
+        end
+      end
+    end
+  end
+end
diff --git a/lib/convertkit/resources/subscriber_bulk_tag_failure_response.rb b/lib/convertkit/resources/subscriber_bulk_tag_failure_response.rb
new file mode 100644
index 0000000..4aa5452
--- /dev/null
+++ b/lib/convertkit/resources/subscriber_bulk_tag_failure_response.rb
@@ -0,0 +1,12 @@
+module ConvertKit
+  module Resources
+    class SubscriberBulkTagFailureResponse
+      attr_accessor :tagging, :errors
+
+      def initialize(response)
+        @tagging = SubscriberTagResponse.new(response['tagging']) if response['tagging']
+        @errors = response['errors']
+      end
+    end
+  end
+end
diff --git a/lib/convertkit/resources/subscriber_response.rb b/lib/convertkit/resources/subscriber_response.rb
index 63da643..4b1103b 100644
--- a/lib/convertkit/resources/subscriber_response.rb
+++ b/lib/convertkit/resources/subscriber_response.rb
@@ -12,5 +12,17 @@ def initialize(response)
         @created_at = ConvertKit::Utils.to_datetime(response['created_at'])
       end
     end
+
+    class TaggedSubscriberResponse
+      attr_accessor :id, :first_name, :email, :created_at, :tagged_at
+
+      def initialize(response)
+        @id = response['id']
+        @first_name = response['first_name']
+        @email = response['email_address']
+        @created_at = ConvertKit::Utils.to_datetime(response['created_at'])
+        @tagged_at = ConvertKit::Utils.to_datetime(response['tagged_at'])
+      end
+    end
   end
 end
diff --git a/lib/convertkit/resources/subscriber_tag_response.rb b/lib/convertkit/resources/subscriber_tag_response.rb
new file mode 100644
index 0000000..c198f79
--- /dev/null
+++ b/lib/convertkit/resources/subscriber_tag_response.rb
@@ -0,0 +1,12 @@
+module ConvertKit
+  module Resources
+    class SubscriberTagResponse
+      attr_accessor :tag_id, :subscriber_id
+
+      def initialize(response)
+        @tag_id = response['tag_id']
+        @subscriber_id = response['subscriber_id']
+      end
+    end
+  end
+end
diff --git a/lib/convertkit/resources/tags.rb b/lib/convertkit/resources/tags.rb
index b9625f4..e06fe4a 100644
--- a/lib/convertkit/resources/tags.rb
+++ b/lib/convertkit/resources/tags.rb
@@ -23,7 +23,18 @@ def list
       def create(name)
         response = @client.post(PATH, { name: name })
 
-        TagResponse.new(response)
+        TagResponse.new(response['tag'])
+      end
+
+      # Update the name of a Tag
+      # See https://developers.kit.com/v4#update-tag-name for details
+      # @param [Integer] tag_id
+      # @param [Hash] options
+      # @option options [String] :name New name for Tag
+      def update(tag_id, options = {})
+        request_options = options.slice(:name)
+        response = @client.put("#{PATH}/#{tag_id}", request_options)
+        TagResponse.new(response['tag'])
       end
 
       # Tags a subscriber
@@ -85,6 +96,30 @@ def subscriptions(tag_id, options = {})
 
         SubscriptionsResponse.new(response)
       end
+
+      # Bulk add tag to subscribers
+      # @param [Array<Hash>] taggings
+      # @option taggings [String] :tag_id
+      # @option taggings [String] :subscriber_id
+      def bulk_add_to_subscribers(taggings = [])
+        raise ArgumentError, 'taggings must be an array' unless taggings.is_a?(Array)
+
+        response = @client.post("bulk/#{PATH}/subscribers", { taggings: taggings })
+
+        ConvertKit::Resources::SubscriberBulkAddTagResponse.new(response)
+      end
+
+      # Bulk remove tag from subscribers
+      # @param [Array<Hash>] taggings
+      # @option taggings [String] :tag_id
+      # @option taggings [String] :subscriber_id
+      def bulk_remove_from_subscribers(taggings = [])
+        raise ArgumentError, 'taggings must be an array' unless taggings.is_a?(Array)
+
+        response = @client.delete("bulk/#{PATH}/subscribers", { taggings: taggings })
+
+        ConvertKit::Resources::SubscriberBulkRemoveTagResponse.new(response)
+      end
     end
   end
 end
diff --git a/spec/lib/convertkit/connection_spec.rb b/spec/lib/convertkit/connection_spec.rb
index 866b272..2744425 100644
--- a/spec/lib/convertkit/connection_spec.rb
+++ b/spec/lib/convertkit/connection_spec.rb
@@ -3,7 +3,7 @@
 
   describe '#initialize' do
     it 'creates a new Faraday connection' do
-      expect(Faraday).to receive(:new).with(url: url, headers: {'content-type' => 'application/json' })
+      expect(Faraday).to receive(:new).with(url: url, headers: {'Content-Type' => 'application/json' })
       ConvertKit::Connection.new(url)
     end
   end
diff --git a/spec/lib/convertkit/developer_client_spec.rb b/spec/lib/convertkit/developer_client_spec.rb
new file mode 100644
index 0000000..3e71098
--- /dev/null
+++ b/spec/lib/convertkit/developer_client_spec.rb
@@ -0,0 +1,13 @@
+describe ConvertKit::DeveloperClient do
+  let(:connection) { double('connection') }
+
+  describe '#initialize' do
+    it 'sets the api_key' do
+      expect(ConvertKit::Connection).to receive(:new)
+                                          .with(ConvertKit::Client::API_URL, api_key: 'test_token')
+                                          .and_return(connection)
+      client = ConvertKit::DeveloperClient.new('test_token')
+      expect(client.instance_variable_get(:@connection)).to eq(connection)
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/lib/convertkit/resources/tags_spec.rb b/spec/lib/convertkit/resources/tags_spec.rb
index b8edb8d..5625291 100644
--- a/spec/lib/convertkit/resources/tags_spec.rb
+++ b/spec/lib/convertkit/resources/tags_spec.rb
@@ -31,10 +31,10 @@
 
     context 'when name is a string' do
       it 'creates a tag' do
-        response = { 'id' => 1, 'name' => 'tag_name', account_id: 1, state: 'available', 'created_at' => '2023-08-09T04:30:00Z', updated_at: '2023-08-09T04:30:00Z'}
+        response = {'tag' => { 'id' => 1, 'name' => 'tag_name', account_id: 1, state: 'available', 'created_at' => '2023-08-09T04:30:00Z', updated_at: '2023-08-09T04:30:00Z'}}
         expect(client).to receive(:post).with('tags', {name: 'tag_name'}).and_return(response)
         tags_response = tags.create('tag_name')
-        validate_tag(tags_response, response)
+        validate_tag(tags_response, response['tag'])
       end
     end
   end
@@ -142,4 +142,100 @@
       validate_subscriptions(tag_subscriptions_response, response)
     end
   end
+
+  describe '#bulk_add_to_subscribers' do
+    let(:tags) { ConvertKit::Resources::Tags.new(client) }
+    let(:taggings) { [{'tag_id' => 1, 'subscriber_id' => 1}] }
+    let(:response) do
+      {
+        'subscribers' => [{
+          'id' => 1,
+          'first_name' => 'foo',
+          'email_address' => 'foo@bar.com',
+          'created_at' => '2023-08-09T04:30:00Z',
+          'tagged_at' => '2023-08-09T04:30:00Z'
+        }],
+        'failures' => []
+      }
+    end
+
+    context 'with taggings provided' do
+      it 'tags listed subscribers' do
+        expect(client).to receive(:post).with('bulk/tags/subscribers', {taggings: taggings}).and_return(response)
+
+        tags_response = tags.bulk_add_to_subscribers(taggings)
+        validate_tagged_subscribers(tags_response, response)
+      end
+    end
+
+    # Failures are not well documented in the API documentation
+    context 'with failures' do
+      let(:response) do
+        {
+          'subscribers' => [],
+          'failures' => [{
+            'tagging' => {
+              'subscriber_id' => 1,
+              'tag_id' => 2,
+            },
+            'errors' => ['Test error message']
+          }]
+        }
+      end
+
+      it 'return failures with subscriber and error message' do
+        expect(client).to receive(:post).with('bulk/tags/subscribers', {taggings: taggings}).and_return(response)
+
+        tags_response = tags.bulk_add_to_subscribers(taggings)
+        expect(tags_response.failures.count).to eq(1)
+        expect(tags_response.failures.first.tagging.subscriber_id).to eq(1)
+        expect(tags_response.failures.first.tagging.tag_id).to eq(2)
+        expect(tags_response.failures.first.errors.first).to eq('Test error message')
+      end
+    end
+  end
+
+  describe '#bulk_remove_from_subscribers' do
+    let(:tags) { ConvertKit::Resources::Tags.new(client) }
+    let(:taggings) { [{'tag_id' => 1, 'subscriber_id' => 1}] }
+    let(:response) do
+      {
+        'failures' => []
+      }
+    end
+
+    context 'with taggings provided' do
+      it 'return no failures' do
+        expect(client).to receive(:delete).with('bulk/tags/subscribers', {taggings: taggings}).and_return(response)
+
+        tags_response = tags.bulk_remove_from_subscribers(taggings)
+        expect(tags_response.failures).to be_empty
+      end
+    end
+
+    # Failures are not well documented in the API documentation
+    context 'with failures' do
+      let(:response) do
+        {
+          'failures' => [{
+            'tagging' => {
+              'subscriber_id' => 1,
+              'tag_id' => 2,
+            },
+            'errors' => ['Test error message']
+          }]
+        }
+      end
+
+      it 'return failures with subscriber and error message' do
+        expect(client).to receive(:delete).with('bulk/tags/subscribers', {taggings: taggings}).and_return(response)
+
+        tags_response = tags.bulk_remove_from_subscribers(taggings)
+        expect(tags_response.failures.count).to eq(1)
+        expect(tags_response.failures.first.tagging.subscriber_id).to eq(1)
+        expect(tags_response.failures.first.tagging.tag_id).to eq(2)
+        expect(tags_response.failures.first.errors.first).to eq('Test error message')
+      end
+    end
+  end
 end
diff --git a/spec/validators/subscriber_validators.rb b/spec/validators/subscriber_validators.rb
index dbc2548..9b646d5 100644
--- a/spec/validators/subscriber_validators.rb
+++ b/spec/validators/subscriber_validators.rb
@@ -19,6 +19,18 @@ def validate_subscribers(subscribers, values)
       end
     end
 
+    def validate_tagged_subscribers(subscribers, values)
+      subscribers.subscribers.each_with_index do |subscriber, index|
+        values = values['subscribers'][index]
+
+        expect(subscriber.id).to eq(values['id'])
+        expect(subscriber.first_name).to eq(values['first_name'])
+        expect(subscriber.email).to eq(values['email_address'])
+        expect(subscriber.created_at).to eq(DateTime.parse(values['created_at'])) unless values.fetch('created_at', '').strip.empty?
+        expect(subscriber.tagged_at).to eq(DateTime.parse(values['tagged_at'])) unless values.fetch('tagged_at', '').strip.empty?
+      end
+    end
+
     def validate_bulk_create_failure(bulk_create_failure_response, values)
       expect(bulk_create_failure_response.errors).to match_array(values['errors']) if values['errors']
       validate_subscriber(bulk_create_failure_response.subscriber, values['subscriber']) if values['subscriber']