diff --git a/.release-please-manifest.json b/.release-please-manifest.json
index abeb3cc..88e4c44 100644
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,3 +1,3 @@
 {
-  ".": "4.19.2"
+  ".": "4.20.0"
 }
\ No newline at end of file
diff --git a/.stats.yml b/.stats.yml
index 9e3b99b..809d9f7 100644
--- a/.stats.yml
+++ b/.stats.yml
@@ -1,4 +1,4 @@
-configured_endpoints: 138
-openapi_spec_url: https://storage.googleapis.com/stainless-sdk-openapi-specs/courier/courier-11e1931d767cef402bbed5a965746d1933ae72db0f41881860593a0b1424fd80.yml
-openapi_spec_hash: 9def941805f233f8761c4bdae88f6137
-config_hash: 6c3a754258f0f77e9032a90a478ab76d
+configured_endpoints: 139
+openapi_spec_url: https://storage.googleapis.com/stainless-sdk-openapi-specs/courier/courier-def1e982add0411bf64b48cdf5e4f2c1b85b9bd0ada0d5e6fc4869afa85e0bff.yml
+openapi_spec_hash: 5d129cdf800798bcd4a93585ec89c696
+config_hash: dcd58abf1e56b114bdce22336ca3d570
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3f1a41a..c1119db 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,14 @@
 # Changelog
 
+## 4.20.0 (2026-07-14)
+
+Full Changelog: [v4.19.2...v4.20.0](https://github.com/trycourier/courier-ruby/compare/v4.19.2...v4.20.0)
+
+### Features
+
+* Document POST /notifications/{id}/duplicate [C-18607] ([#165](https://github.com/trycourier/courier-ruby/issues/165)) ([212644c](https://github.com/trycourier/courier-ruby/commit/212644cd49ac7b108944831e04289d2e9e073b7d))
+* Merge pull request [#149](https://github.com/trycourier/courier-ruby/issues/149) from trycourier/geraldosilva/c-19201-notification-template-subscription-topic-id ([cd697fa](https://github.com/trycourier/courier-ruby/commit/cd697fa2d3b49db32db582dae1789ab03706ced5))
+
 ## 4.19.2 (2026-07-10)
 
 Full Changelog: [v4.19.1...v4.19.2](https://github.com/trycourier/courier-ruby/compare/v4.19.1...v4.19.2)
diff --git a/Gemfile.lock b/Gemfile.lock
index de77cce..e60f699 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -11,7 +11,7 @@ GIT
 PATH
   remote: .
   specs:
-    trycourier (4.19.2)
+    trycourier (4.20.0)
       cgi
       connection_pool
 
diff --git a/lib/courier.rb b/lib/courier.rb
index e6fa372..35cb3d7 100644
--- a/lib/courier.rb
+++ b/lib/courier.rb
@@ -260,6 +260,7 @@
 require_relative "courier/models/notification_content_get_response"
 require_relative "courier/models/notification_content_mutation_response"
 require_relative "courier/models/notification_create_params"
+require_relative "courier/models/notification_duplicate_params"
 require_relative "courier/models/notification_get_content"
 require_relative "courier/models/notification_list_params"
 require_relative "courier/models/notification_list_response"
diff --git a/lib/courier/models.rb b/lib/courier/models.rb
index f7ec0a6..4e19e6a 100644
--- a/lib/courier/models.rb
+++ b/lib/courier/models.rb
@@ -360,6 +360,8 @@ module Courier
 
   NotificationCreateParams = Courier::Models::NotificationCreateParams
 
+  NotificationDuplicateParams = Courier::Models::NotificationDuplicateParams
+
   NotificationElementPutRequest = Courier::Models::NotificationElementPutRequest
 
   NotificationGetContent = Courier::Models::NotificationGetContent
diff --git a/lib/courier/models/notification_duplicate_params.rb b/lib/courier/models/notification_duplicate_params.rb
new file mode 100644
index 0000000..8e38bc6
--- /dev/null
+++ b/lib/courier/models/notification_duplicate_params.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+module Courier
+  module Models
+    # @see Courier::Resources::Notifications#duplicate
+    class NotificationDuplicateParams < Courier::Internal::Type::BaseModel
+      extend Courier::Internal::Type::RequestParameters::Converter
+      include Courier::Internal::Type::RequestParameters
+
+      # @!attribute id
+      #
+      #   @return [String]
+      required :id, String
+
+      # @!method initialize(id:, request_options: {})
+      #   @param id [String]
+      #   @param request_options [Courier::RequestOptions, Hash{Symbol=>Object}]
+    end
+  end
+end
diff --git a/lib/courier/models/notification_template_summary.rb b/lib/courier/models/notification_template_summary.rb
index 382cee9..2c09e81 100644
--- a/lib/courier/models/notification_template_summary.rb
+++ b/lib/courier/models/notification_template_summary.rb
@@ -35,6 +35,13 @@ class NotificationTemplateSummary < Courier::Internal::Type::BaseModel
       #   @return [Array<String>]
       required :tags, Courier::Internal::Type::ArrayOf[String]
 
+      # @!attribute subscription_topic_id
+      #   The linked subscription (preference) topic of the published version. Omitted
+      #   when no topic is linked or the template has never been published.
+      #
+      #   @return [String, nil]
+      optional :subscription_topic_id, String
+
       # @!attribute updated
       #   Epoch milliseconds of last update.
       #
@@ -47,7 +54,10 @@ class NotificationTemplateSummary < Courier::Internal::Type::BaseModel
       #   @return [String, nil]
       optional :updater, String
 
-      # @!method initialize(id:, created:, creator:, name:, state:, tags:, updated: nil, updater: nil)
+      # @!method initialize(id:, created:, creator:, name:, state:, tags:, subscription_topic_id: nil, updated: nil, updater: nil)
+      #   Some parameter documentations has been truncated, see
+      #   {Courier::Models::NotificationTemplateSummary} for more details.
+      #
       #   V2 (CDS) template summary returned in list responses.
       #
       #   @param id [String]
@@ -62,6 +72,8 @@ class NotificationTemplateSummary < Courier::Internal::Type::BaseModel
       #
       #   @param tags [Array<String>]
       #
+      #   @param subscription_topic_id [String] The linked subscription (preference) topic of the published version. Omitted whe
+      #
       #   @param updated [Integer] Epoch milliseconds of last update.
       #
       #   @param updater [String] User ID of the last updater.
diff --git a/lib/courier/resources/notifications.rb b/lib/courier/resources/notifications.rb
index 43cab1a..410d855 100644
--- a/lib/courier/resources/notifications.rb
+++ b/lib/courier/resources/notifications.rb
@@ -110,6 +110,31 @@ def archive(id, params = {})
         )
       end
 
+      # Duplicate a notification template. Creates a standalone copy within the same
+      # workspace and environment, with " COPY" appended to the title. The copy clones
+      # the source draft's tags, brand, subscription topic, routing strategy, channels,
+      # and content, and is always created as a standalone template (it is not linked to
+      # any journey or broadcast, even if the source was). Templates that are scoped to
+      # a journey or a broadcast cannot be duplicated through this endpoint.
+      #
+      # @overload duplicate(id, request_options: {})
+      #
+      # @param id [String] Template ID (nt\_ prefix).
+      #
+      # @param request_options [Courier::RequestOptions, Hash{Symbol=>Object}, nil]
+      #
+      # @return [Courier::Models::NotificationTemplateResponse]
+      #
+      # @see Courier::Models::NotificationDuplicateParams
+      def duplicate(id, params = {})
+        @client.request(
+          method: :post,
+          path: ["notifications/%1$s/duplicate", id],
+          model: Courier::NotificationTemplateResponse,
+          options: params[:request_options]
+        )
+      end
+
       # List versions of a notification template.
       #
       # @overload list_versions(id, cursor: nil, limit: nil, request_options: {})
diff --git a/lib/courier/version.rb b/lib/courier/version.rb
index 6766905..960b373 100644
--- a/lib/courier/version.rb
+++ b/lib/courier/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Courier
-  VERSION = "4.19.2"
+  VERSION = "4.20.0"
 end
diff --git a/rbi/courier/models.rbi b/rbi/courier/models.rbi
index 4a10e90..4647a7e 100644
--- a/rbi/courier/models.rbi
+++ b/rbi/courier/models.rbi
@@ -329,6 +329,8 @@ module Courier
 
   NotificationCreateParams = Courier::Models::NotificationCreateParams
 
+  NotificationDuplicateParams = Courier::Models::NotificationDuplicateParams
+
   NotificationElementPutRequest = Courier::Models::NotificationElementPutRequest
 
   NotificationGetContent = Courier::Models::NotificationGetContent
diff --git a/rbi/courier/models/notification_duplicate_params.rbi b/rbi/courier/models/notification_duplicate_params.rbi
new file mode 100644
index 0000000..8a44e15
--- /dev/null
+++ b/rbi/courier/models/notification_duplicate_params.rbi
@@ -0,0 +1,38 @@
+# typed: strong
+
+module Courier
+  module Models
+    class NotificationDuplicateParams < Courier::Internal::Type::BaseModel
+      extend Courier::Internal::Type::RequestParameters::Converter
+      include Courier::Internal::Type::RequestParameters
+
+      OrHash =
+        T.type_alias do
+          T.any(
+            Courier::NotificationDuplicateParams,
+            Courier::Internal::AnyHash
+          )
+        end
+
+      sig { returns(String) }
+      attr_accessor :id
+
+      sig do
+        params(
+          id: String,
+          request_options: Courier::RequestOptions::OrHash
+        ).returns(T.attached_class)
+      end
+      def self.new(id:, request_options: {})
+      end
+
+      sig do
+        override.returns(
+          { id: String, request_options: Courier::RequestOptions }
+        )
+      end
+      def to_hash
+      end
+    end
+  end
+end
diff --git a/rbi/courier/models/notification_template_summary.rbi b/rbi/courier/models/notification_template_summary.rbi
index 1539c38..1d1d393 100644
--- a/rbi/courier/models/notification_template_summary.rbi
+++ b/rbi/courier/models/notification_template_summary.rbi
@@ -31,6 +31,14 @@ module Courier
       sig { returns(T::Array[String]) }
       attr_accessor :tags
 
+      # The linked subscription (preference) topic of the published version. Omitted
+      # when no topic is linked or the template has never been published.
+      sig { returns(T.nilable(String)) }
+      attr_reader :subscription_topic_id
+
+      sig { params(subscription_topic_id: String).void }
+      attr_writer :subscription_topic_id
+
       # Epoch milliseconds of last update.
       sig { returns(T.nilable(Integer)) }
       attr_reader :updated
@@ -54,6 +62,7 @@ module Courier
           name: String,
           state: Courier::NotificationTemplateSummary::State::OrSymbol,
           tags: T::Array[String],
+          subscription_topic_id: String,
           updated: Integer,
           updater: String
         ).returns(T.attached_class)
@@ -67,6 +76,9 @@ module Courier
         name:,
         state:,
         tags:,
+        # The linked subscription (preference) topic of the published version. Omitted
+        # when no topic is linked or the template has never been published.
+        subscription_topic_id: nil,
         # Epoch milliseconds of last update.
         updated: nil,
         # User ID of the last updater.
@@ -83,6 +95,7 @@ module Courier
             name: String,
             state: Courier::NotificationTemplateSummary::State::TaggedSymbol,
             tags: T::Array[String],
+            subscription_topic_id: String,
             updated: Integer,
             updater: String
           }
diff --git a/rbi/courier/resources/notifications.rbi b/rbi/courier/resources/notifications.rbi
index 00efdc6..bdb459a 100644
--- a/rbi/courier/resources/notifications.rbi
+++ b/rbi/courier/resources/notifications.rbi
@@ -79,6 +79,25 @@ module Courier
       )
       end
 
+      # Duplicate a notification template. Creates a standalone copy within the same
+      # workspace and environment, with " COPY" appended to the title. The copy clones
+      # the source draft's tags, brand, subscription topic, routing strategy, channels,
+      # and content, and is always created as a standalone template (it is not linked to
+      # any journey or broadcast, even if the source was). Templates that are scoped to
+      # a journey or a broadcast cannot be duplicated through this endpoint.
+      sig do
+        params(
+          id: String,
+          request_options: Courier::RequestOptions::OrHash
+        ).returns(Courier::NotificationTemplateResponse)
+      end
+      def duplicate(
+        # Template ID (nt\_ prefix).
+        id,
+        request_options: {}
+      )
+      end
+
       # List versions of a notification template.
       sig do
         params(
diff --git a/sig/courier/models.rbs b/sig/courier/models.rbs
index 893de37..19cb7bd 100644
--- a/sig/courier/models.rbs
+++ b/sig/courier/models.rbs
@@ -317,6 +317,8 @@ module Courier
 
   class NotificationCreateParams = Courier::Models::NotificationCreateParams
 
+  class NotificationDuplicateParams = Courier::Models::NotificationDuplicateParams
+
   class NotificationElementPutRequest = Courier::Models::NotificationElementPutRequest
 
   class NotificationGetContent = Courier::Models::NotificationGetContent
diff --git a/sig/courier/models/notification_duplicate_params.rbs b/sig/courier/models/notification_duplicate_params.rbs
new file mode 100644
index 0000000..f99586b
--- /dev/null
+++ b/sig/courier/models/notification_duplicate_params.rbs
@@ -0,0 +1,20 @@
+module Courier
+  module Models
+    type notification_duplicate_params =
+      { id: String } & Courier::Internal::Type::request_parameters
+
+    class NotificationDuplicateParams < Courier::Internal::Type::BaseModel
+      extend Courier::Internal::Type::RequestParameters::Converter
+      include Courier::Internal::Type::RequestParameters
+
+      attr_accessor id: String
+
+      def initialize: (
+        id: String,
+        ?request_options: Courier::request_opts
+      ) -> void
+
+      def to_hash: -> { id: String, request_options: Courier::RequestOptions }
+    end
+  end
+end
diff --git a/sig/courier/models/notification_template_summary.rbs b/sig/courier/models/notification_template_summary.rbs
index 81b6b6e..aa141c7 100644
--- a/sig/courier/models/notification_template_summary.rbs
+++ b/sig/courier/models/notification_template_summary.rbs
@@ -8,6 +8,7 @@ module Courier
         name: String,
         state: Courier::Models::NotificationTemplateSummary::state,
         tags: ::Array[String],
+        subscription_topic_id: String,
         updated: Integer,
         updater: String
       }
@@ -25,6 +26,10 @@ module Courier
 
       attr_accessor tags: ::Array[String]
 
+      attr_reader subscription_topic_id: String?
+
+      def subscription_topic_id=: (String) -> String
+
       attr_reader updated: Integer?
 
       def updated=: (Integer) -> Integer
@@ -40,6 +45,7 @@ module Courier
         name: String,
         state: Courier::Models::NotificationTemplateSummary::state,
         tags: ::Array[String],
+        ?subscription_topic_id: String,
         ?updated: Integer,
         ?updater: String
       ) -> void
@@ -51,6 +57,7 @@ module Courier
         name: String,
         state: Courier::Models::NotificationTemplateSummary::state,
         tags: ::Array[String],
+        subscription_topic_id: String,
         updated: Integer,
         updater: String
       }
diff --git a/sig/courier/resources/notifications.rbs b/sig/courier/resources/notifications.rbs
index 66b875d..c5251f5 100644
--- a/sig/courier/resources/notifications.rbs
+++ b/sig/courier/resources/notifications.rbs
@@ -24,6 +24,11 @@ module Courier
 
       def archive: (String id, ?request_options: Courier::request_opts) -> nil
 
+      def duplicate: (
+        String id,
+        ?request_options: Courier::request_opts
+      ) -> Courier::NotificationTemplateResponse
+
       def list_versions: (
         String id,
         ?cursor: String,
diff --git a/test/courier/resources/notifications_test.rb b/test/courier/resources/notifications_test.rb
index 37d0525..3003277 100644
--- a/test/courier/resources/notifications_test.rb
+++ b/test/courier/resources/notifications_test.rb
@@ -60,6 +60,16 @@ def test_archive
     end
   end
 
+  def test_duplicate
+    skip("Mock server tests are disabled")
+
+    response = @courier.notifications.duplicate("id")
+
+    assert_pattern do
+      response => Courier::NotificationTemplateResponse
+    end
+  end
+
   def test_list_versions
     skip("Mock server tests are disabled")