diff --git a/libraries/management/commands/release_tasks.py b/libraries/management/commands/release_tasks.py
index b8f900941..0bceb1ec9 100644
--- a/libraries/management/commands/release_tasks.py
+++ b/libraries/management/commands/release_tasks.py
@@ -61,6 +61,11 @@ def set_tasks(self):
             Action("Updating slack activity buckets", ["fetch_slack_activity"]),
             Action("Updating website statistics", self.update_website_statistics),
             Action("Importing mailing list counts", self.import_ml_counts),
+            # Last, so every source it reads has already been refreshed above.
+            Action(
+                "Backfilling achievements",
+                ["backfill_achievements", "--trigger", "pipeline"],
+            ),
             # Action("Generating report", self.generate_report),
         ]
 
diff --git a/libraries/tasks.py b/libraries/tasks.py
index b69652828..51dace9e8 100644
--- a/libraries/tasks.py
+++ b/libraries/tasks.py
@@ -280,6 +280,17 @@ def update_authors_and_maintainers():
     call_command("update_maintainers")
     call_command("update_library_version_authors", "--clean")
     app.signature("users.tasks.recompute_displayed_profile_roles").apply_async()
+    # Only the sources whose upstream data just changed. A blanket backfill would
+    # also sweep the commit and review tables this task never touches.
+    call_command(
+        "backfill_achievements",
+        "--source",
+        "library-authoring",
+        "--source",
+        "library-maintenance",
+        "--source",
+        "library-versioning",
+    )
 
 
 @app.task
@@ -296,6 +307,10 @@ def update_commits(token=None, clean=False, min_version=""):
         )
     logger.info("update_commits finished.")
     app.signature("users.tasks.recompute_displayed_profile_roles").apply_async()
+    # No achievement backfill here on purpose: this runs as a step of the
+    # release_tasks command, which sweeps every source once at the end. Calling
+    # it here too would walk the whole Commit table twice per release. Ad hoc
+    # runs use the "Backfill achievements" button in the badges admin.
     return commits_handled
 
 
diff --git a/libraries/tests/test_tasks.py b/libraries/tests/test_tasks.py
index cffa59341..510ea8b45 100644
--- a/libraries/tests/test_tasks.py
+++ b/libraries/tests/test_tasks.py
@@ -164,3 +164,56 @@ def test_update_library_version_website_adoc_no_stable_release():
     with patch("libraries.tasks.store_library_version_website_adoc") as mock_store:
         update_library_version_website_adoc()
     mock_store.assert_not_called()
+
+
+@patch("libraries.tasks.call_command")
+def test_update_authors_and_maintainers_backfills_only_library_sources(mock_call):
+    """A blanket backfill here would sweep the commit and review tables too."""
+    from libraries.tasks import update_authors_and_maintainers
+
+    update_authors_and_maintainers()
+
+    backfills = [
+        c for c in mock_call.call_args_list if c.args[0] == "backfill_achievements"
+    ]
+    assert len(backfills) == 1
+    assert set(backfills[0].args[1:]) == {
+        "--source",
+        "library-authoring",
+        "library-maintenance",
+        "library-versioning",
+    }
+
+
+@patch("libraries.tasks.LibraryUpdater")
+@patch("libraries.tasks.call_command")
+def test_update_commits_does_not_backfill(mock_call, _mock_updater, db):
+    """release_tasks sweeps every source once; a call here would double it."""
+    from libraries.tasks import update_commits
+
+    update_commits()
+
+    assert not [
+        c for c in mock_call.call_args_list if c.args[0] == "backfill_achievements"
+    ]
+
+
+@patch("libraries.tasks.call_command")
+def test_release_tasks_delegates_the_backfill_to_the_command(mock_call):
+    """The sweep is an Action inside release_tasks, not a trailing extra call."""
+    from libraries.management.commands.release_tasks import ReleaseTasksManager
+    from libraries.tasks import release_tasks
+
+    release_tasks("https://example.com")
+
+    assert [c.args[0] for c in mock_call.call_args_list] == ["release_tasks"]
+    manager = ReleaseTasksManager(base_uri="https://example.com", user_id=None)
+    sweeps = [
+        task
+        for task in manager.tasks
+        if isinstance(task.handler, list) and task.handler[0] == "backfill_achievements"
+    ]
+    assert [task.description for task in sweeps] == ["Backfilling achievements"]
+    # Tagged, so the sync log can tell the weekly job from a person pressing a
+    # button when support asks what moved a member's count.
+    assert sweeps[0].handler == ["backfill_achievements", "--trigger", "pipeline"]