diff --git a/app/jobs/regular/fast_track_topic_gist.rb b/app/jobs/regular/fast_track_topic_gist.rb
index 8885bee30..a20d18179 100644
--- a/app/jobs/regular/fast_track_topic_gist.rb
+++ b/app/jobs/regular/fast_track_topic_gist.rb
@@ -16,7 +16,7 @@ def execute(args)
       gist = summarizer.existing_summary
       return if gist.present? && (!gist.outdated || gist.created_at >= 5.minutes.ago)
 
-      summarizer.force_summarize(Discourse.system_user)
+      summarizer.summarize(Discourse.system_user)
     end
   end
 end
diff --git a/app/jobs/scheduled/summaries_backfill.rb b/app/jobs/scheduled/summaries_backfill.rb
index 34ea2d532..10dcc7195 100644
--- a/app/jobs/scheduled/summaries_backfill.rb
+++ b/app/jobs/scheduled/summaries_backfill.rb
@@ -18,7 +18,8 @@ def execute(_args)
         backfill_candidates(gist_t)
           .limit(current_budget(gist_t))
           .each do |topic|
-            DiscourseAi::Summarization.topic_gist(topic).force_summarize(system_user)
+            strategy = DiscourseAi::Summarization.topic_gist(topic)
+            try_summarize(strategy, system_user, topic)
           end
       end
 
@@ -26,10 +27,25 @@ def execute(_args)
       backfill_candidates(complete_t)
         .limit(current_budget(complete_t))
         .each do |topic|
-          DiscourseAi::Summarization.topic_summary(topic).force_summarize(system_user)
+          strategy = DiscourseAi::Summarization.topic_summary(topic)
+          try_summarize(strategy, system_user, topic)
         end
     end
 
+    def try_summarize(strategy, user, topic)
+      existing_summary = strategy.existing_summary
+
+      if existing_summary.blank? || existing_summary.outdated
+        strategy.summarize(user)
+      else
+        # Hiding or deleting a post, and creating a small action alters the Topic#highest_post_number.
+        # We use this as a quick way to select potential backfill candidates without relying on original_content_sha.
+        # At this point, we are confident the summary doesn't need to be regenerated so something other than a regular reply
+        # caused the number to change in the topic.
+        existing_summary.update!(highest_target_number: topic.highest_post_number)
+      end
+    end
+
     def backfill_candidates(summary_type)
       max_age_days = SiteSetting.ai_summary_backfill_topic_max_age_days
 
@@ -45,12 +61,12 @@ def backfill_candidates(summary_type)
         .where(
           <<~SQL, # (1..1) gets stored ad (1..2).
           ais.id IS NULL OR (
-            UPPER(ais.content_range) < topics.highest_post_number + 1 
-            AND ais.created_at < (current_timestamp - INTERVAL '5 minutes')
+            ais.highest_target_number < topics.highest_post_number
+            AND ais.updated_at < (current_timestamp - INTERVAL '5 minutes')
           )
         SQL
         )
-        .order("ais.created_at DESC NULLS FIRST, topics.last_posted_at DESC")
+        .order("ais.updated_at DESC NULLS FIRST, topics.last_posted_at DESC")
     end
 
     def current_budget(type)
diff --git a/app/models/ai_summary.rb b/app/models/ai_summary.rb
index 30b23351b..458c5f181 100644
--- a/app/models/ai_summary.rb
+++ b/app/models/ai_summary.rb
@@ -1,6 +1,9 @@
 # frozen_string_literal: true
 
 class AiSummary < ActiveRecord::Base
+  # TODO remove this line 01-3-2025
+  self.ignored_columns = %i[content_range]
+
   belongs_to :target, polymorphic: true
 
   enum :summary_type, { complete: 0, gist: 1 }
@@ -15,14 +18,20 @@ def self.store!(strategy, llm_model, summary, og_content, human:)
           target_id: strategy.target.id,
           target_type: strategy.target.class.name,
           algorithm: llm_model.name,
-          content_range: (content_ids.first..content_ids.last),
+          highest_target_number: strategy.highest_target_number,
           summarized_text: summary,
           original_content_sha: build_sha(content_ids.join),
           summary_type: strategy.type,
           origin: !!human ? origins[:human] : origins[:system],
         },
         unique_by: %i[target_id target_type summary_type],
-        update_only: %i[summarized_text original_content_sha algorithm origin content_range],
+        update_only: %i[
+          summarized_text
+          original_content_sha
+          algorithm
+          origin
+          highest_target_number
+        ],
       )
       .first
       .then { AiSummary.find_by(id: _1["id"]) }
@@ -45,17 +54,17 @@ def outdated
 #
 # Table name: ai_summaries
 #
-#  id                   :bigint           not null, primary key
-#  target_id            :integer          not null
-#  target_type          :string           not null
-#  content_range        :int4range
-#  summarized_text      :string           not null
-#  original_content_sha :string           not null
-#  algorithm            :string           not null
-#  created_at           :datetime         not null
-#  updated_at           :datetime         not null
-#  summary_type         :integer          default("complete"), not null
-#  origin               :integer
+#  id                    :bigint           not null, primary key
+#  target_id             :integer          not null
+#  target_type           :string           not null
+#  summarized_text       :string           not null
+#  original_content_sha  :string           not null
+#  algorithm             :string           not null
+#  created_at            :datetime         not null
+#  updated_at            :datetime         not null
+#  summary_type          :integer          default("complete"), not null
+#  origin                :integer
+#  highest_target_number :integer          not null
 #
 # Indexes
 #
diff --git a/app/serializers/ai_topic_summary_serializer.rb b/app/serializers/ai_topic_summary_serializer.rb
index 738f843e4..7ffff9e20 100644
--- a/app/serializers/ai_topic_summary_serializer.rb
+++ b/app/serializers/ai_topic_summary_serializer.rb
@@ -13,15 +13,6 @@ def can_regenerate
   end
 
   def new_posts_since_summary
-    # Postgres uses discrete range types for int4range, which means
-    # (1..2) is stored as (1...3).
-    #
-    # We use Range#max to work around this, which in the case above always returns 2.
-    # Be careful with using Range#end here, it could lead to unexpected results as:
-    #
-    # (1..2).end => 2
-    # (1...3).end => 3
-
-    object.target.highest_post_number.to_i - object.content_range&.max.to_i
+    object.target.highest_post_number.to_i - object.highest_target_number.to_i
   end
 end
diff --git a/db/migrate/20250115173456_add_highest_target_number_to_ai_summary.rb b/db/migrate/20250115173456_add_highest_target_number_to_ai_summary.rb
new file mode 100644
index 000000000..9a208a3e9
--- /dev/null
+++ b/db/migrate/20250115173456_add_highest_target_number_to_ai_summary.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+class AddHighestTargetNumberToAiSummary < ActiveRecord::Migration[7.2]
+  def up
+    add_column :ai_summaries, :highest_target_number, :integer, null: false
+
+    execute <<~SQL
+      UPDATE ai_summaries SET highest_target_number = GREATEST(UPPER(content_range) - 1, 1)
+    SQL
+  end
+
+  def down
+    drop_column :ai_summaries, :highest_target_number
+  end
+end
diff --git a/db/post_migrate/20250115181147_drop_ai_summaries_content_range.rb b/db/post_migrate/20250115181147_drop_ai_summaries_content_range.rb
new file mode 100644
index 000000000..726b08588
--- /dev/null
+++ b/db/post_migrate/20250115181147_drop_ai_summaries_content_range.rb
@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+class DropAiSummariesContentRange < ActiveRecord::Migration[7.2]
+  DROPPED_COLUMNS ||= { ai_summaries: %i[content_range] }
+
+  def up
+    DROPPED_COLUMNS.each { |table, columns| Migration::ColumnDropper.execute_drop(table, columns) }
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end
diff --git a/lib/summarization/fold_content.rb b/lib/summarization/fold_content.rb
index 32bf97791..831d311eb 100644
--- a/lib/summarization/fold_content.rb
+++ b/lib/summarization/fold_content.rb
@@ -21,6 +21,8 @@ def initialize(llm, strategy, persist_summaries: true)
       # @param &on_partial_blk { Block - Optional } - The passed block will get called with the LLM partial response alongside a cancel function.
       # Note: The block is only called with results of the final summary, not intermediate summaries.
       #
+      # This method doesn't care if we already have an up to date summary. It always regenerate.
+      #
       # @returns { AiSummary } - Resulting summary.
       def summarize(user, &on_partial_blk)
         base_summary = ""
@@ -68,11 +70,6 @@ def delete_cached_summaries!
         AiSummary.where(target: strategy.target, summary_type: strategy.type).destroy_all
       end
 
-      def force_summarize(user, &on_partial_blk)
-        @persist_summaries = true
-        summarize(user, &on_partial_blk)
-      end
-
       private
 
       attr_reader :persist_summaries
diff --git a/lib/summarization/strategies/chat_messages.rb b/lib/summarization/strategies/chat_messages.rb
index 1f3aad6d8..2f073d71a 100644
--- a/lib/summarization/strategies/chat_messages.rb
+++ b/lib/summarization/strategies/chat_messages.rb
@@ -8,6 +8,10 @@ def type
           AiSummary.summary_types[:complete]
         end
 
+        def highest_target_number
+          nil # We don't persist so we can return nil.
+        end
+
         def initialize(target, since)
           super(target)
           @since = since
diff --git a/lib/summarization/strategies/hot_topic_gists.rb b/lib/summarization/strategies/hot_topic_gists.rb
index 1708f2b86..b3e888761 100644
--- a/lib/summarization/strategies/hot_topic_gists.rb
+++ b/lib/summarization/strategies/hot_topic_gists.rb
@@ -12,6 +12,10 @@ def feature
           "gists"
         end
 
+        def highest_target_number
+          target.highest_post_number
+        end
+
         def targets_data
           op_post_number = 1
 
@@ -38,6 +42,7 @@ def targets_data
                 .limit(20)
                 .pluck(:post_number)
           end
+
           posts_data =
             Post
               .where(topic_id: target.id)
diff --git a/lib/summarization/strategies/topic_summary.rb b/lib/summarization/strategies/topic_summary.rb
index c252fe33b..e97c391a9 100644
--- a/lib/summarization/strategies/topic_summary.rb
+++ b/lib/summarization/strategies/topic_summary.rb
@@ -8,6 +8,10 @@ def type
           AiSummary.summary_types[:complete]
         end
 
+        def highest_target_number
+          target.highest_post_number
+        end
+
         def targets_data
           posts_data =
             (target.has_summary? ? best_replies : pick_selection).pluck(
diff --git a/spec/fabricators/ai_summary_fabricator.rb b/spec/fabricators/ai_summary_fabricator.rb
index 250ae943a..d596dbaba 100644
--- a/spec/fabricators/ai_summary_fabricator.rb
+++ b/spec/fabricators/ai_summary_fabricator.rb
@@ -7,6 +7,7 @@
   target { Fabricate(:topic) }
   summary_type AiSummary.summary_types[:complete]
   origin AiSummary.origins[:human]
+  highest_target_number 1
 end
 
 Fabricator(:topic_ai_gist, from: :ai_summary) do
diff --git a/spec/jobs/scheduled/summaries_backfill_spec.rb b/spec/jobs/scheduled/summaries_backfill_spec.rb
index 2764055dd..401f4d205 100644
--- a/spec/jobs/scheduled/summaries_backfill_spec.rb
+++ b/spec/jobs/scheduled/summaries_backfill_spec.rb
@@ -44,13 +44,13 @@
     end
 
     it "ignores up to date summaries" do
-      Fabricate(:ai_summary, target: topic, content_range: (1..2))
+      Fabricate(:ai_summary, target: topic, highest_target_number: 2, updated_at: 10.minutes.ago)
 
       expect(subject.backfill_candidates(type)).to be_empty
     end
 
-    it "ignores outdated summaries created less than five minutes ago" do
-      Fabricate(:ai_summary, target: topic, content_range: (1..1), created_at: 4.minutes.ago)
+    it "ignores outdated summaries updated less than five minutes ago" do
+      Fabricate(:ai_summary, target: topic, highest_target_number: 1, updated_at: 4.minutes.ago)
 
       expect(subject.backfill_candidates(type)).to be_empty
     end
@@ -66,7 +66,7 @@
       topic_2 =
         Fabricate(:topic, word_count: 200, last_posted_at: 2.minutes.ago, highest_post_number: 1)
       topic.update!(last_posted_at: 1.minute.ago)
-      Fabricate(:ai_summary, target: topic, created_at: 1.hour.ago, content_range: (1..1))
+      Fabricate(:ai_summary, target: topic, updated_at: 1.hour.ago, highest_target_number: 1)
 
       expect(subject.backfill_candidates(type).map(&:id)).to contain_exactly(topic_2.id, topic.id)
     end
@@ -84,13 +84,13 @@
       topic_2 =
         Fabricate(:topic, word_count: 200, last_posted_at: 2.minutes.ago, highest_post_number: 1)
       topic.update!(last_posted_at: 1.minute.ago)
-      Fabricate(:ai_summary, target: topic, created_at: 3.hours.ago, content_range: (1..1))
-      Fabricate(:topic_ai_gist, target: topic, created_at: 3.hours.ago, content_range: (1..1))
+      Fabricate(:ai_summary, target: topic, updated_at: 3.hours.ago, highest_target_number: 1)
+      Fabricate(:topic_ai_gist, target: topic, updated_at: 3.hours.ago, highest_target_number: 1)
 
       summary_1 = "Summary of topic_2"
       gist_1 = "Gist of topic_2"
-      summary_2 = "Summary of topic"
-      gist_2 = "Gist of topic"
+      summary_2 = "Updated summary of topic"
+      gist_2 = "Updated gist of topic"
 
       DiscourseAi::Completions::Llm.with_prepared_responses(
         [gist_1, gist_2, summary_1, summary_2],
@@ -100,6 +100,32 @@
       expect(AiSummary.gist.find_by(target: topic_2).summarized_text).to eq(gist_1)
       expect(AiSummary.complete.find_by(target: topic).summarized_text).to eq(summary_2)
       expect(AiSummary.gist.find_by(target: topic).summarized_text).to eq(gist_2)
+
+      # Queue has to be empty if we just generated all summaries
+      expect(subject.backfill_candidates(AiSummary.summary_types[:complete])).to be_empty
+      expect(subject.backfill_candidates(AiSummary.summary_types[:gist])).to be_empty
+
+      # Queue still empty when they are up to date and time passes.
+      AiSummary.update_all(updated_at: 20.minutes.ago)
+      expect(subject.backfill_candidates(AiSummary.summary_types[:complete])).to be_empty
+      expect(subject.backfill_candidates(AiSummary.summary_types[:gist])).to be_empty
+    end
+
+    it "updates the highest_target_number if the summary turned to be up to date" do
+      existing_summary =
+        Fabricate(
+          :ai_summary,
+          target: topic,
+          updated_at: 3.hours.ago,
+          highest_target_number: topic.highest_post_number,
+        )
+      og_highest_post_number = topic.highest_post_number
+      topic.update!(highest_post_number: og_highest_post_number + 1)
+
+      # No prepared responses here. We don't perform a completion call.
+      subject.execute({})
+
+      expect(existing_summary.reload.highest_target_number).to eq(og_highest_post_number + 1)
     end
   end
 end
diff --git a/spec/lib/guardian_extensions_spec.rb b/spec/lib/guardian_extensions_spec.rb
index 589b362a2..7e3bb6f0a 100644
--- a/spec/lib/guardian_extensions_spec.rb
+++ b/spec/lib/guardian_extensions_spec.rb
@@ -26,13 +26,7 @@
       end
 
       it "returns true if there is a cached summary" do
-        AiSummary.create!(
-          target: topic,
-          summarized_text: "test",
-          original_content_sha: "123",
-          algorithm: "test",
-          summary_type: AiSummary.summary_types[:complete],
-        )
+        Fabricate(:ai_summary, target: topic)
 
         expect(guardian.can_see_summary?(topic)).to eq(true)
       end
@@ -66,13 +60,7 @@
       end
 
       it "returns true for anons when there is a cached summary" do
-        AiSummary.create!(
-          target: topic,
-          summarized_text: "test",
-          original_content_sha: "123",
-          algorithm: "test",
-          summary_type: AiSummary.summary_types[:complete],
-        )
+        Fabricate(:ai_summary, target: topic)
 
         expect(guardian.can_see_summary?(topic)).to eq(true)
       end
diff --git a/spec/requests/summarization/summary_controller_spec.rb b/spec/requests/summarization/summary_controller_spec.rb
index 493d7c856..01ab28bdb 100644
--- a/spec/requests/summarization/summary_controller_spec.rb
+++ b/spec/requests/summarization/summary_controller_spec.rb
@@ -13,15 +13,7 @@
 
     context "when streaming" do
       it "return a cached summary with json payload and does not trigger job if it exists" do
-        section =
-          AiSummary.create!(
-            target: topic,
-            summarized_text: "test",
-            algorithm: "test",
-            original_content_sha: "test",
-            summary_type: AiSummary.summary_types[:complete],
-          )
-
+        summary = Fabricate(:ai_summary, target: topic)
         sign_in(Fabricate(:admin))
 
         get "/discourse-ai/summarization/t/#{topic.id}.json?stream=true"
@@ -29,8 +21,10 @@
         expect(response.status).to eq(200)
         expect(Jobs::StreamTopicAiSummary.jobs.size).to eq(0)
 
-        summary = response.parsed_body
-        expect(summary.dig("ai_topic_summary", "summarized_text")).to eq(section.summarized_text)
+        response_summary = response.parsed_body
+        expect(response_summary.dig("ai_topic_summary", "summarized_text")).to eq(
+          summary.summarized_text,
+        )
       end
     end
 
@@ -42,21 +36,15 @@
       end
 
       it "returns a cached summary" do
-        section =
-          AiSummary.create!(
-            target: topic,
-            summarized_text: "test",
-            algorithm: "test",
-            original_content_sha: "test",
-            summary_type: AiSummary.summary_types[:complete],
-          )
-
+        summary = Fabricate(:ai_summary, target: topic)
         get "/discourse-ai/summarization/t/#{topic.id}.json"
 
         expect(response.status).to eq(200)
 
-        summary = response.parsed_body
-        expect(summary.dig("ai_topic_summary", "summarized_text")).to eq(section.summarized_text)
+        response_summary = response.parsed_body
+        expect(response_summary.dig("ai_topic_summary", "summarized_text")).to eq(
+          summary.summarized_text,
+        )
       end
     end
 
@@ -90,15 +78,15 @@
           get "/discourse-ai/summarization/t/#{topic.id}.json"
 
           expect(response.status).to eq(200)
-          summary = response.parsed_body["ai_topic_summary"]
-          section = AiSummary.last
-
-          expect(section.summarized_text).to eq(summary_text)
-          expect(summary["summarized_text"]).to eq(section.summarized_text)
-          expect(summary["algorithm"]).to eq("fake")
-          expect(summary["outdated"]).to eq(false)
-          expect(summary["can_regenerate"]).to eq(true)
-          expect(summary["new_posts_since_summary"]).to be_zero
+          response_summary = response.parsed_body["ai_topic_summary"]
+          summary = AiSummary.last
+
+          expect(summary.summarized_text).to eq(summary_text)
+          expect(response_summary["summarized_text"]).to eq(summary.summarized_text)
+          expect(response_summary["algorithm"]).to eq("fake")
+          expect(response_summary["outdated"]).to eq(false)
+          expect(response_summary["can_regenerate"]).to eq(true)
+          expect(response_summary["new_posts_since_summary"]).to be_zero
         end
       end
 
@@ -129,21 +117,16 @@
       end
 
       it "returns a cached summary" do
-        section =
-          AiSummary.create!(
-            target: topic,
-            summarized_text: "test",
-            algorithm: "test",
-            original_content_sha: "test",
-            summary_type: AiSummary.summary_types[:complete],
-          )
+        summary = Fabricate(:ai_summary, target: topic)
 
         get "/discourse-ai/summarization/t/#{topic.id}.json"
 
         expect(response.status).to eq(200)
 
-        summary = response.parsed_body
-        expect(summary.dig("ai_topic_summary", "summarized_text")).to eq(section.summarized_text)
+        response_summary = response.parsed_body
+        expect(response_summary.dig("ai_topic_summary", "summarized_text")).to eq(
+          summary.summarized_text,
+        )
       end
     end
   end
diff --git a/spec/services/discourse_ai/topic_summarization_spec.rb b/spec/services/discourse_ai/topic_summarization_spec.rb
index eca5a13ef..a75dd527c 100644
--- a/spec/services/discourse_ai/topic_summarization_spec.rb
+++ b/spec/services/discourse_ai/topic_summarization_spec.rb
@@ -20,7 +20,7 @@ def assert_summary_is_cached(topic, summary_response)
       cached_summary =
         AiSummary.find_by(target: topic, summary_type: AiSummary.summary_types[:complete])
 
-      expect(cached_summary.content_range).to cover(*topic.posts.map(&:post_number))
+      expect(cached_summary.highest_target_number).to eq(topic.highest_post_number)
       expect(cached_summary.summarized_text).to eq(summary)
       expect(cached_summary.original_content_sha).to be_present
       expect(cached_summary.algorithm).to eq("fake")
diff --git a/spec/system/summarization/topic_summarization_spec.rb b/spec/system/summarization/topic_summarization_spec.rb
index 36caea2e6..45ffd7a66 100644
--- a/spec/system/summarization/topic_summarization_spec.rb
+++ b/spec/system/summarization/topic_summarization_spec.rb
@@ -16,6 +16,8 @@
   let(:topic_page) { PageObjects::Pages::Topic.new }
   let(:summary_box) { PageObjects::Components::AiSummaryTrigger.new }
 
+  fab!(:ai_summary) { Fabricate(:ai_summary, target: topic, summarized_text: "This is a summary") }
+
   before do
     group.add(current_user)
 
@@ -27,16 +29,6 @@
   end
 
   context "when a summary is cached" do
-    before do
-      AiSummary.create!(
-        target: topic,
-        summarized_text: summarization_result,
-        algorithm: "test",
-        original_content_sha: "test",
-        summary_type: AiSummary.summary_types[:complete],
-      )
-    end
-
     it "displays it" do
       topic_page.visit_topic(topic)
       summary_box.click_summarize
@@ -45,15 +37,6 @@
   end
 
   context "when a summary is outdated" do
-    before do
-      AiSummary.create!(
-        target: topic,
-        summarized_text: summarization_result,
-        algorithm: "test",
-        original_content_sha: "test",
-        summary_type: AiSummary.summary_types[:complete],
-      )
-    end
     fab!(:new_post) do
       Fabricate(
         :post,