diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 1f1131b32bf1d..10d741914dc39 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,11 @@
+*   Deprecate using `insert_all`/`upsert_all` with unpersisted records in associations.
+
+    Using these methods on associations containing unpersisted records will now
+    show a deprecation warning, as the unpersisted records will be lost after
+    the operation. This will become an error in Rails 8.2.
+
+    *Nick Schwaderer*
+
 *   Introduce versions formatter for the schema dumper.
 
     It is now possible to override how schema dumper formats versions information inside the
diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index 930179ed0ecd4..4f07ca5cc1079 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -1128,7 +1128,18 @@ def pretty_print(pp) # :nodoc:
       %w(insert insert_all insert! insert_all! upsert upsert_all).each do |method|
         class_eval <<~RUBY, __FILE__, __LINE__ + 1
           def #{method}(...)
-            scope.#{method}(...).tap { reset }
+            if loaded? && @association&.target&.any? { |r| r.new_record? }
+              ActiveRecord.deprecator.warn(<<~MSG)
+                Using #{method} on association with unpersisted records
+                (\#{to_a.reject(&:persisted?).map(&:class).uniq.join(', ')})
+                is deprecated. The unpersisted records will be lost after this operation.
+                Please either persist your records first or store them separately before
+                calling #{method}. This will become an error in Rails 8.1.
+              MSG
+              scope.#{method}(...)
+            else
+              scope.#{method}(...).tap { reset }
+            end
           end
         RUBY
       end
diff --git a/activerecord/test/cases/insert_all_test.rb b/activerecord/test/cases/insert_all_test.rb
index fb39dce3d1f32..4823c969ec56b 100644
--- a/activerecord/test/cases/insert_all_test.rb
+++ b/activerecord/test/cases/insert_all_test.rb
@@ -16,7 +16,7 @@ class ReadonlyNameBook < Book
 end
 
 class InsertAllTest < ActiveRecord::TestCase
-  fixtures :books
+  fixtures :books, :authors
 
   def setup
     Arel::Table.engine = nil # should not rely on the global Arel::Table.engine
@@ -863,6 +863,32 @@ def test_insert_all_when_table_name_contains_database
     end
   end
 
+  def test_insert_all_with_unpersisted_records_deprecation
+    author = Author.create!(name: "Rafael")
+    author.books.build(title: "Unpersisted Book")
+    author.books.load
+
+    assert_deprecated(ActiveRecord.deprecator) do
+      author.books.insert_all([{ title: "New Book" }])
+    end
+
+    assert_equal 1, author.books.size
+    assert_equal ["Unpersisted Book"], author.books.pluck(:title)
+  end
+
+  def test_insert_all_resets_without_unpersisted_records
+    author = Author.create!(name: "Rafael")
+    author.books.load
+
+    assert_not_deprecated(ActiveRecord.deprecator) do
+      author.books.insert_all([{ title: "New Book" }])
+    end
+
+    assert_not_predicate author.books, :loaded?
+    assert_equal 1, author.books.size
+    assert_equal ["New Book"], author.books.pluck(:title)
+  end
+
   private
     def capture_log_output
       output = StringIO.new