diff --git a/keyserver/src/scripts/test-threadstore-reductions.js b/keyserver/src/scripts/test-threadstore-reductions.js
--- a/keyserver/src/scripts/test-threadstore-reductions.js
+++ b/keyserver/src/scripts/test-threadstore-reductions.js
@@ -1,20 +1,65 @@
 // @flow
 
 import ashoat from 'lib/facts/ashoat.js';
+import type { RawMessageInfo } from 'lib/types/message-types.js';
+import { threadTypes } from 'lib/types/thread-types-enum.js';
+import type { RawThreadInfos } from 'lib/types/thread-types.js';
 
 import { main } from './utils.js';
+import { fetchMessageInfos } from '../fetchers/message-fetchers.js';
 import { fetchThreadInfos } from '../fetchers/thread-fetchers.js';
 import { createScriptViewer } from '../session/scripts.js';
 
 const viewer = createScriptViewer(ashoat.id);
 
+const oneWeekAgo = Date.now() - 7 * 24 * 60 * 60 * 1000;
+const messageSelectionCriteria = { joinedThreads: true, newerThan: oneWeekAgo };
+
 async function testThreadStoreReductions() {
-  const { threadInfos } = await fetchThreadInfos(viewer);
+  const [{ threadInfos }, { rawMessageInfos }] = await Promise.all([
+    fetchThreadInfos(viewer),
+    fetchMessageInfos(viewer, messageSelectionCriteria, 1),
+  ]);
   const beforeReductions = JSON.stringify(threadInfos);
   const beforeBytes = new Blob([beforeReductions]).size;
   console.log(
     `before reductions, Ashoat's ThreadStore is ${beforeBytes} bytes large`,
   );
+
+  const withoutOldSidebars = filterOutOldSidebars(threadInfos, rawMessageInfos);
+  const withoutOldSidebarsString = JSON.stringify(withoutOldSidebars);
+  const withoutOldSidebarsBytes = new Blob([withoutOldSidebarsString]).size;
+  console.log(
+    "after filtering out old sidebars, Ashoat's ThreadStore is " +
+      `${withoutOldSidebarsBytes} bytes large`,
+  );
+}
+
+function filterOutOldSidebars(
+  threadInfos: RawThreadInfos,
+  messageInfos: $ReadOnlyArray<RawMessageInfo>,
+): RawThreadInfos {
+  const newestTimePerThread = new Map();
+  for (const messageInfo of messageInfos) {
+    const { threadID, time } = messageInfo;
+    const currentNewest = newestTimePerThread.get(threadID);
+    if (!currentNewest || currentNewest < time) {
+      newestTimePerThread.set(threadID, time);
+    }
+  }
+
+  const filtered = {};
+  for (const threadID in threadInfos) {
+    const threadInfo = threadInfos[threadID];
+    const latestUpdate = newestTimePerThread.get(threadID);
+    if (
+      threadInfo.type !== threadTypes.SIDEBAR ||
+      (latestUpdate && latestUpdate >= oneWeekAgo)
+    ) {
+      filtered[threadID] = threadInfo;
+    }
+  }
+  return filtered;
 }
 
 main([testThreadStoreReductions]);