diff --git a/app/controllers/course/gradebook_controller.rb b/app/controllers/course/gradebook_controller.rb
index fe739dc11e..c54fe2d6f7 100644
--- a/app/controllers/course/gradebook_controller.rb
+++ b/app/controllers/course/gradebook_controller.rb
@@ -5,6 +5,7 @@ class Course::GradebookController < Course::ComponentController
   def index
     respond_to do |format|
       format.json do
+        @weighted_view_enabled = @settings.weighted_view_enabled
         @published_assessments = fetch_published_assessments
         @categories, @tabs = fetch_categories_and_tabs
         @students = fetch_students
@@ -18,12 +19,27 @@ def index
     end
   end
 
+  def update_weights
+    authorize! :manage_gradebook_weights, current_course
+    updates = update_weights_params[:weights].map do |entry|
+      { tab_id: entry[:tabId].to_i, weight: entry[:weight].to_i }
+    end
+    Course::Assessment::Tab.update_gradebook_weights(course: current_course, updates: updates)
+    render json: { weights: updates.map { |u| { tabId: u[:tab_id], weight: u[:weight] } } }
+  rescue ActiveRecord::RecordInvalid, ActiveRecord::RecordNotFound => e
+    render json: { errors: { base: e.message } }, status: :unprocessable_entity
+  end
+
   private
 
   def authorize_read_gradebook!
     authorize! :read_gradebook, current_course
   end
 
+  def update_weights_params
+    params.permit(weights: [:tabId, :weight])
+  end
+
   def component
     current_component_host[:course_gradebook_component]
   end
diff --git a/app/models/components/course/gradebook_ability_component.rb b/app/models/components/course/gradebook_ability_component.rb
index e084be9509..d54a56cca6 100644
--- a/app/models/components/course/gradebook_ability_component.rb
+++ b/app/models/components/course/gradebook_ability_component.rb
@@ -4,10 +4,8 @@ module Course::GradebookAbilityComponent
 
   def define_permissions
     can :read_gradebook, Course, id: course.id if course_user&.staff?
-    if course_user&.manager_or_owner?
-      can :manage_gradebook_weights, Course, id: course.id # Reserved for weights-editing endpoint in follow-on PR
-      can :manage_gradebook_settings, Course, id: course.id
-    end
+    can :manage_gradebook_weights, Course, id: course.id if course_user&.manager_or_owner?
+    can :manage_gradebook_settings, Course, id: course.id if course_user&.manager_or_owner?
     super
   end
 end
diff --git a/app/models/course/assessment/tab.rb b/app/models/course/assessment/tab.rb
index 305bfc5e1c..4013558f34 100644
--- a/app/models/course/assessment/tab.rb
+++ b/app/models/course/assessment/tab.rb
@@ -29,6 +29,30 @@ class Course::Assessment::Tab < ApplicationRecord
       select('(array_agg(title))[0:3]')
   end)
 
+  # Bulk-updates the gradebook_weight for a set of tabs belonging to the given course.
+  # Raises ActiveRecord::RecordNotFound if any tab_id does not belong to the course.
+  # Raises ActiveRecord::RecordInvalid if any weight fails validation; the transaction is rolled back.
+  #
+  # @param course [Course]
+  # @param updates [Array<Hash>] array of { tab_id: Integer, weight: Integer }
+  def self.update_gradebook_weights(course:, updates:)
+    course_tab_ids = course.assessment_tabs.pluck(:id).to_set
+    tab_ids_to_update = updates.map { |e| e[:tab_id] }
+
+    tab_ids_to_update.each do |tab_id|
+      raise ActiveRecord::RecordNotFound unless course_tab_ids.include?(tab_id)
+    end
+
+    tabs_by_id = where(id: tab_ids_to_update).index_by(&:id)
+
+    transaction do
+      updates.each do |entry|
+        tab = tabs_by_id[entry[:tab_id]]
+        tab.update!(gradebook_weight: entry[:weight])
+      end
+    end
+  end
+
   # Returns a boolean value indicating if there are other tabs
   # besides this one remaining in its category.
   #
diff --git a/app/views/course/gradebook/index.json.jbuilder b/app/views/course/gradebook/index.json.jbuilder
index 8c67f0a070..edd6daa4d1 100644
--- a/app/views/course/gradebook/index.json.jbuilder
+++ b/app/views/course/gradebook/index.json.jbuilder
@@ -1,4 +1,7 @@
 # frozen_string_literal: true
+json.weightedViewEnabled @weighted_view_enabled
+json.canManageWeights can?(:manage_gradebook_weights, current_course)
+
 json.categories @categories do |cat|
   json.id cat.id
   json.title cat.title
@@ -8,6 +11,7 @@ json.tabs @tabs do |tab|
   json.id tab.id
   json.title tab.title
   json.categoryId tab.category_id
+  json.gradebookWeight tab.gradebook_weight if @weighted_view_enabled
 end
 
 json.assessments @published_assessments do |assessment|
diff --git a/config/routes.rb b/config/routes.rb
index 0b6f16f368..6838d77f24 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -501,6 +501,7 @@
 
       resource :gradebook, only: [] do
         get '/' => 'gradebook#index'
+        patch '/weights' => 'gradebook#update_weights'
       end
 
       scope module: :discussion do
diff --git a/spec/controllers/course/gradebook_controller_spec.rb b/spec/controllers/course/gradebook_controller_spec.rb
index 4b21113c31..01fc03c37d 100644
--- a/spec/controllers/course/gradebook_controller_spec.rb
+++ b/spec/controllers/course/gradebook_controller_spec.rb
@@ -185,5 +185,148 @@
         end
       end
     end
+
+    describe 'PATCH update_weights' do
+      let(:manager) { create(:course_manager, course: course) }
+      let(:ta) { create(:course_teaching_assistant, course: course) }
+      let(:student) { create(:course_student, course: course) }
+      let(:category) { create(:course_assessment_category, course: course) }
+      let!(:tab1) { create(:course_assessment_tab, category: category) }
+      let!(:tab2) { create(:course_assessment_tab, category: category) }
+
+      let(:valid_payload) do
+        { weights: [{ tabId: tab1.id, weight: 60 }, { tabId: tab2.id, weight: 40 }] }
+      end
+
+      context 'as manager' do
+        before { controller_sign_in(controller, manager.user) }
+
+        it 'updates and returns 200' do
+          patch :update_weights, params: { course_id: course.id, **valid_payload }, format: :json
+          expect(response).to have_http_status(:ok)
+          expect(tab1.reload.gradebook_weight).to eq(60)
+          expect(tab2.reload.gradebook_weight).to eq(40)
+        end
+
+        it 'accepts sum < 100' do
+          patch :update_weights,
+                params: { course_id: course.id, weights: [tabId: tab1.id, weight: 30] },
+                format: :json
+          expect(response).to have_http_status(:ok)
+        end
+
+        it 'accepts sum > 100' do
+          patch :update_weights,
+                params: { course_id: course.id,
+                          weights: [{ tabId: tab1.id, weight: 70 }, { tabId: tab2.id, weight: 70 }] },
+                format: :json
+          expect(response).to have_http_status(:ok)
+        end
+
+        it 'rejects negative with 422 and no partial write' do
+          tab1.update!(gradebook_weight: 10)
+          patch :update_weights,
+                params: { course_id: course.id,
+                          weights: [{ tabId: tab1.id, weight: 50 }, { tabId: tab2.id, weight: -1 }] },
+                format: :json
+          expect(response).to have_http_status(:unprocessable_entity)
+          expect(tab1.reload.gradebook_weight).to eq(10)
+        end
+
+        it 'rejects >100 with 422' do
+          patch :update_weights,
+                params: { course_id: course.id, weights: [tabId: tab1.id, weight: 101] },
+                format: :json
+          expect(response).to have_http_status(:unprocessable_entity)
+        end
+
+        it 'rejects foreign tab id with 422' do
+          other_course = create(:course)
+          other_tab = create(:course_assessment_tab,
+                             category: create(:course_assessment_category, course: other_course))
+          patch :update_weights,
+                params: { course_id: course.id, weights: [tabId: other_tab.id, weight: 50] },
+                format: :json
+          expect(response).to have_http_status(:unprocessable_entity)
+        end
+      end
+
+      context 'as TA' do
+        before { controller_sign_in(controller, ta.user) }
+        it 'is denied' do
+          expect do
+            patch :update_weights, params: { course_id: course.id, **valid_payload }, format: :json
+          end.to raise_error(CanCan::AccessDenied)
+        end
+      end
+
+      context 'as student' do
+        before { controller_sign_in(controller, student.user) }
+        it 'is denied' do
+          expect do
+            patch :update_weights, params: { course_id: course.id, **valid_payload }, format: :json
+          end.to raise_error(CanCan::AccessDenied)
+        end
+      end
+
+      context 'when setting is disabled' do
+        before { controller_sign_in(controller, manager.user) }
+
+        it 'still allows update (storage independent of display)' do
+          patch :update_weights, params: { course_id: course.id, **valid_payload }, format: :json
+          expect(response).to have_http_status(:ok)
+          expect(tab1.reload.gradebook_weight).to eq(60)
+        end
+      end
+    end
+
+    describe 'GET index — weighted view fields' do
+      render_views
+      let(:manager) { create(:course_manager, course: course) }
+      let(:ta) { create(:course_teaching_assistant, course: course) }
+      let(:category) { create(:course_assessment_category, course: course) }
+      let!(:tab) { create(:course_assessment_tab, category: category, gradebook_weight: 30) }
+      let!(:assessment) do
+        create(:course_assessment_assessment, :published_with_mcq_question,
+               course: course, tab: tab)
+      end
+
+      context 'when setting is disabled (default)' do
+        before { controller_sign_in(controller, manager.user) }
+
+        it 'returns weightedViewEnabled false and omits gradebookWeight per tab' do
+          get :index, params: { course_id: course.id }, format: :json
+          body = JSON.parse(response.body)
+          expect(body['weightedViewEnabled']).to eq(false)
+          tab_json = body['tabs'].find { |t| t['id'] == tab.id }
+          expect(tab_json).not_to have_key('gradebookWeight')
+        end
+      end
+
+      context 'when setting is enabled' do
+        before do
+          ctx = Struct.new(:current_course, :key).new(course, Course::GradebookComponent.key)
+          Course::Settings::GradebookComponent.new(ctx).weighted_view_enabled = true
+          course.save!
+        end
+
+        it 'includes weightedViewEnabled true and gradebookWeight per tab for manager' do
+          controller_sign_in(controller, manager.user)
+          get :index, params: { course_id: course.id }, format: :json
+          body = JSON.parse(response.body)
+          expect(body['weightedViewEnabled']).to eq(true)
+          expect(body['canManageWeights']).to eq(true)
+          tab_json = body['tabs'].find { |t| t['id'] == tab.id }
+          expect(tab_json['gradebookWeight']).to eq(30)
+        end
+
+        it 'returns canManageWeights false for TA' do
+          controller_sign_in(controller, ta.user)
+          get :index, params: { course_id: course.id }, format: :json
+          body = JSON.parse(response.body)
+          expect(body['canManageWeights']).to eq(false)
+        end
+      end
+    end
   end
 end
diff --git a/spec/models/course/assessment/tab_spec.rb b/spec/models/course/assessment/tab_spec.rb
index 6eaea2f517..b546671032 100644
--- a/spec/models/course/assessment/tab_spec.rb
+++ b/spec/models/course/assessment/tab_spec.rb
@@ -53,5 +53,46 @@
         expect(tab).not_to be_valid
       end
     end
+
+    describe '.update_gradebook_weights' do
+      let(:course) { create(:course) }
+      let(:category) { create(:course_assessment_category, course: course) }
+      let(:tab1) { create(:course_assessment_tab, category: category) }
+      let(:tab2) { create(:course_assessment_tab, category: category) }
+
+      it 'updates given tabs' do
+        described_class.update_gradebook_weights(
+          course: course,
+          updates: [{ tab_id: tab1.id, weight: 60 }, { tab_id: tab2.id, weight: 40 }]
+        )
+        expect(tab1.reload.gradebook_weight).to eq(60)
+        expect(tab2.reload.gradebook_weight).to eq(40)
+      end
+
+      it 'is transactional — invalid value rolls back everything' do
+        tab1.update!(gradebook_weight: 10)
+        tab2.update!(gradebook_weight: 20)
+        expect do
+          described_class.update_gradebook_weights(
+            course: course,
+            updates: [{ tab_id: tab1.id, weight: 50 }, { tab_id: tab2.id, weight: 999 }]
+          )
+        end.to raise_error(ActiveRecord::RecordInvalid)
+        expect(tab1.reload.gradebook_weight).to eq(10)
+        expect(tab2.reload.gradebook_weight).to eq(20)
+      end
+
+      it 'rejects foreign tab_id' do
+        other_course = create(:course)
+        other_tab = create(:course_assessment_tab,
+                           category: create(:course_assessment_category, course: other_course))
+        expect do
+          described_class.update_gradebook_weights(
+            course: course,
+            updates: [tab_id: other_tab.id, weight: 50]
+          )
+        end.to raise_error(ActiveRecord::RecordNotFound)
+      end
+    end
   end
 end