diff --git a/tests/browser/replay-feed.test.js b/tests/browser/replay-feed.test.js
index edec3d5..781eed4 100644
--- a/tests/browser/replay-feed.test.js
+++ b/tests/browser/replay-feed.test.js
@@ -77,3 +77,32 @@ test("replay-feed waits out Retry-After", async () => {
     delete globalThis.fetch;
   }
 });
+
+test("replay-feed keeps a batch alive past the page unless it is over the keepalive budget", async () => {
+  const feed = await import("../../web/replay-feed.js?keepalive");
+  const posts = [];
+  globalThis.fetch = async (_url, init) => {
+    posts.push({ events: JSON.parse(init.body).events.length, keepalive: init.keepalive });
+    return { status: 204, headers: { get: () => null } };
+  };
+  try {
+    feed.initReplay({
+      state: { interviewId: "i1" },
+      nodes: {},
+      recordingEnabled: true,
+      consentVersion: "v1",
+      replayVersion: 1,
+    });
+    feed.recordReplay("lifecycle", { state: "ended", reason: "time_up" });
+    await feed.flushReplay();
+    feed.recordReplay("code", { text: "é".repeat(40_000) });
+    await feed.flushReplay();
+    assert.deepEqual(posts, [
+      { events: 1, keepalive: true },
+      { events: 1, keepalive: false },
+    ]);
+  } finally {
+    feed.closeReplay();
+    delete globalThis.fetch;
+  }
+});
diff --git a/web/replay-feed.js b/web/replay-feed.js
index 3a5c724..98a1530 100644
--- a/web/replay-feed.js
+++ b/web/replay-feed.js
@@ -25,6 +25,7 @@ const REPLAY_FLUSH_MS = 1000;
 const REPLAY_MAX_BATCH = 32;
 const REPLAY_RETRY_MS = 60_000;
 const REPLAY_RETRY_MAX_MS = 120_000;
+const REPLAY_KEEPALIVE_MAX_BYTES = 64 * 1024;
 
 /// How often the clock and the problem heading are restated.
 ///
@@ -121,11 +122,19 @@ async function sendQueuedBatch() {
     return;
   }
   const batch = replayQueue.splice(0, REPLAY_MAX_BATCH);
+  const body = JSON.stringify({ events: batch });
   try {
+    // Kept alive so a batch already on its way survives the tab closing. The
+    // interview's last events are flushed as the candidate reaches the report,
+    // which is the moment a candidate is most likely to leave, and a plain
+    // fetch is cancelled with the page. Every batch rather than only the last,
+    // because the end may be the one inside a Retry-After window and so go
+    // out on the timer rather than from the call that asked for it.
     const response = await fetch(`/api/interviews/${encodeURIComponent(state.interviewId)}/events`, {
       method: "POST",
       headers: { "Content-Type": "application/json" },
-      body: JSON.stringify({ events: batch }),
+      body,
+      keepalive: new TextEncoder().encode(body).length <= REPLAY_KEEPALIVE_MAX_BYTES,
     });
     // 404 is an interview whose consent has been withdrawn, and quota is an
     // interview that has recorded all it may. Both mean the server will refuse