diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0f5fc4a..7216aa8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Changelog
 
+## 0.15.1 - 2026-09-16
+
+- Use the existing cleanup index when finding expired actor instances. Preserve
+  creation-time fallback for never-used instances and the strict retention cutoff.
+
 ## 0.15.0 - 2026-09-15
 
 - Maintain effect-owner heartbeats during long-running handlers, completion, and
diff --git a/Gemfile.lock b/Gemfile.lock
index e641844..e4f588d 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    solid_objects (0.15.0)
+    solid_objects (0.15.1)
       actioncable (>= 7.1)
       actionpack (>= 7.1)
       actionview (>= 7.1)
@@ -384,7 +384,7 @@ CHECKSUMS
   rubocop-rails-omakase (1.1.0) sha256=2af73ac8ee5852de2919abbd2618af9c15c19b512c4cfc1f9a5d3b6ef009109d
   ruby-progressbar (1.13.0) sha256=80fc9c47a9b640d6834e0dc7b3c94c9df37f08cb072b7761e4a71e22cff29b33
   securerandom (0.4.1) sha256=cc5193d414a4341b6e225f0cb4446aceca8e50d5e1888743fac16987638ea0b1
-  solid_objects (0.15.0)
+  solid_objects (0.15.1)
   sqlite3 (2.9.5-aarch64-linux-gnu) sha256=78075b6337d3d182c6d2b4691049ed45cd220826160c9ea18946bf6a1de200dc
   sqlite3 (2.9.5-aarch64-linux-musl) sha256=18c801185deb4adc01ddb281e8f672a39e3d1729979ca91e39439cd3eac0402d
   sqlite3 (2.9.5-arm-linux-gnu) sha256=1bdfca0c7d63998c60b0f4a8e3c8df2d33800ccc4abd2d612eddbbbc92a4c48b
diff --git a/lib/solid_objects/instance_pruner.rb b/lib/solid_objects/instance_pruner.rb
index d66c13b..3315ea5 100644
--- a/lib/solid_objects/instance_pruner.rb
+++ b/lib/solid_objects/instance_pruner.rb
@@ -33,9 +33,10 @@ def prune
     # @rbs () -> Array[ActiveRecord::Relation[Instance]]
     def policy_relations
       SolidObjects.configuration.instance_retention_by_actor_type.map do |actor_type, retention|
+        cutoff = now - retention
         prunable
           .where(actor_type: actor_type.to_s)
-          .where("COALESCE(last_used_at, created_at) < ?", now - retention)
+          .where("last_used_at < ? OR (last_used_at IS NULL AND created_at < ?)", cutoff, cutoff)
       end
     end
 
diff --git a/lib/solid_objects/version.rb b/lib/solid_objects/version.rb
index 1d09f5e..fad4efd 100644
--- a/lib/solid_objects/version.rb
+++ b/lib/solid_objects/version.rb
@@ -1,5 +1,5 @@
 # rbs_inline: enabled
 
 module SolidObjects
-  VERSION = "0.15.0"
+  VERSION = "0.15.1"
 end
diff --git a/test/integration/instance_pruner_test.rb b/test/integration/instance_pruner_test.rb
new file mode 100644
index 0000000..57c8b84
--- /dev/null
+++ b/test/integration/instance_pruner_test.rb
@@ -0,0 +1,62 @@
+# rbs_inline: enabled
+
+require "database_test_helper"
+
+class InstancePrunerTest < ActiveSupport::TestCase
+  test "retention uses the last use or creation time with a strict cutoff" do
+    now = Time.utc(2026, 9, 16, 12)
+    cutoff = now - 30.days
+    SolidObjects.configuration.instance_retention_by_actor_type = { "expiry-test" => 30.days }
+    expired = [
+      create_instance("unused-old", created_at: cutoff - 1.second, last_used_at: nil),
+      create_instance("used-old", created_at: now, last_used_at: cutoff - 1.second)
+    ]
+    retained = [
+      create_instance("unused-boundary", created_at: cutoff, last_used_at: nil),
+      create_instance("unused-recent", created_at: now, last_used_at: nil),
+      create_instance("used-boundary", created_at: cutoff - 1.day, last_used_at: cutoff),
+      create_instance("used-recent", created_at: cutoff - 1.day, last_used_at: now)
+    ]
+    pruner = SolidObjects::InstancePruner.new(now:)
+
+    assert_equal 2, pruner.preview
+    assert_equal 2, pruner.prune
+    assert_empty SolidObjects::Instance.where(id: expired.map(&:id))
+    assert_equal retained.map(&:id).sort, SolidObjects::Instance.order(:id).pluck(:id)
+  end
+
+  test "MySQL finds expired candidates through the cleanup index" do
+    skip "requires a MySQL query plan" unless database_family == :mysql
+
+    now = Time.utc(2026, 9, 16, 12)
+    SolidObjects.configuration.instance_retention_by_actor_type = { "expiry-test" => 30.days }
+    SolidObjects::Instance.insert_all!(Array.new(2_000) { |index|
+      { actor_type: "expiry-test", actor_id: "recent-#{index}", state: {},
+        created_at: now, updated_at: now, last_used_at: now }
+    })
+    connection = SolidObjects::Instance.connection
+    connection.execute("ANALYZE TABLE solid_objects_instances")
+    statements = []
+    subscriber = ->(*arguments) { statements << arguments.last[:sql].to_s }
+
+    ActiveSupport::Notifications.subscribed(subscriber, "sql.active_record") do
+      assert_equal 0, SolidObjects::InstancePruner.new(now:).prune
+    end
+
+    query = statements.find { |sql| sql.match?(/\ASELECT .* FROM `solid_objects_instances` /) }
+    assert query, "the candidate lookup was not captured"
+    plan = connection.select_all("EXPLAIN FORMAT=TRADITIONAL #{query}").to_a
+      .find { |row| row["table"] == "solid_objects_instances" }
+
+    assert plan, "the candidate table was not present in the query plan"
+    assert_equal "idx_so_instances_cleanup", plan&.fetch("key")
+    assert_operator plan&.fetch("rows").to_i, :<, 20
+  end
+
+  private
+
+  # @rbs (String, created_at: Time, last_used_at: Time?) -> SolidObjects::Instance
+  def create_instance(actor_id, created_at:, last_used_at:)
+    SolidObjects::Instance.create!(actor_type: "expiry-test", actor_id:, created_at:, last_used_at:)
+  end
+end