diff --git a/src/components/Sidebar.test.tsx b/src/components/Sidebar.test.tsx
new file mode 100644
index 0000000..184739f
--- /dev/null
+++ b/src/components/Sidebar.test.tsx
@@ -0,0 +1,96 @@
+// @vitest-environment happy-dom
+(globalThis as { IS_REACT_ACT_ENVIRONMENT?: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+
+import { describe, expect, it, vi, beforeEach } from "vitest";
+import { render, waitFor, cleanup } from "@testing-library/react";
+import { MemoryRouter } from "react-router-dom";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+
+// Stub the auth hook so Sidebar doesn't try to read a token.
+vi.mock("@/auth/useAuth", () => ({
+  useAuth: () => ({ user: { id: 1, username: "admin", role: "admin" }, logout: vi.fn() }),
+}));
+
+// Mutable state so each test can flip the rejected-acks count without
+// re-importing the module. `vi.hoisted` ensures the mock factory closes
+// over the same `state` object across calls.
+const state = vi.hoisted(() => ({
+  unmatchedClaims: 0,
+  unmatchedRemits: 0,
+  rejectedAcks: 0,
+}));
+
+vi.mock("@/hooks/useReconciliation", () => ({
+  useReconciliation: () => ({
+    unmatched: {
+      data: {
+        claims: Array.from({ length: state.unmatchedClaims }),
+        remittances: Array.from({ length: state.unmatchedRemits }),
+      },
+    },
+  }),
+}));
+
+vi.mock("@/hooks/useAckStats", () => ({
+  useAckStats: () => ({
+    data: state.rejectedAcks > 0
+      ? { aggregates: { accepted: 1000, rejected: state.rejectedAcks, received: 1005 } }
+      : undefined,
+  }),
+}));
+
+import { Sidebar } from "./Sidebar";
+
+function renderSidebar() {
+  const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+  return render(
+    <QueryClientProvider client={qc}>
+      <MemoryRouter>
+        <Sidebar />
+      </MemoryRouter>
+    </QueryClientProvider>,
+  );
+}
+
+describe("Sidebar — 999 ACKs rejected badge", () => {
+  beforeEach(() => {
+    cleanup();
+    state.unmatchedClaims = 0;
+    state.unmatchedRemits = 0;
+    state.rejectedAcks = 0;
+  });
+
+  it("shows a '5' badge when 5 segments are rejected", async () => {
+    state.rejectedAcks = 5;
+    const { container } = renderSidebar();
+    await waitFor(() => {
+      const badge = container.querySelector(
+        '[data-testid="sidebar-acks-rejected-badge"]',
+      );
+      expect(badge).not.toBeNull();
+      expect(badge?.textContent).toBe("5");
+    });
+  });
+
+  it("shows '99+' when rejected segments exceed 99", async () => {
+    state.rejectedAcks = 250;
+    const { container } = renderSidebar();
+    await waitFor(() => {
+      const badge = container.querySelector(
+        '[data-testid="sidebar-acks-rejected-badge"]',
+      );
+      expect(badge?.textContent).toBe("99+");
+    });
+  });
+
+  it("hides the badge when there are no rejected acks", async () => {
+    state.rejectedAcks = 0;
+    const { container } = renderSidebar();
+    // Allow the synchronous mock to settle.
+    await waitFor(() => {
+      expect(
+        container.querySelector('[data-testid="sidebar-acks-rejected-badge"]'),
+      ).toBeNull();
+    });
+  });
+});
\ No newline at end of file
diff --git a/src/components/Sidebar.tsx b/src/components/Sidebar.tsx
index 7d4be7c..fbcc07d 100644
--- a/src/components/Sidebar.tsx
+++ b/src/components/Sidebar.tsx
@@ -15,6 +15,7 @@ import {
 } from "lucide-react";
 import { cn } from "@/lib/utils";
 import { useReconciliation } from "@/hooks/useReconciliation";
+import { useAckStats } from "@/hooks/useAckStats";
 import { useAuth } from "@/auth/useAuth";
 
 const nav = [
@@ -43,6 +44,13 @@ export function Sidebar() {
     (unmatched.data?.claims.length ?? 0) +
     (unmatched.data?.remittances.length ?? 0);
 
+  // 999 ACKs — total rejected segments across all ack files. Drives
+  // the badge on the "999 ACKs" nav item so the operator can see
+  // there are rejections to review from any page (mirrors the
+  // Reconciliation unmatched badge above).
+  const { data: ackStats } = useAckStats();
+  const rejectedAckCount = ackStats?.aggregates.rejected ?? 0;
+
   return (
     <aside
       className="hidden md:flex md:w-60 md:flex-col md:fixed md:inset-y-0 z-30 border-r border-border/60 bg-sidebar/80 backdrop-blur-xl"
@@ -152,6 +160,20 @@ export function Sidebar() {
             >
               <CheckCircle2 className="h-3.5 w-3.5" strokeWidth={1.5} />
               <span>999 ACKs</span>
+              {rejectedAckCount > 0 ? (
+                // Rejection-count badge — same right-aligned mono shape
+                // as the Reconciliation unmatched badge above so the
+                // operator's eye finds both at the same scan position.
+                // Warning tone (not signal/destructive) so it doesn't
+                // compete with the more urgent Payer-Rejected lane.
+                <span
+                  className="ml-auto mono text-[10px] text-[hsl(var(--warning))]"
+                  data-testid="sidebar-acks-rejected-badge"
+                  title={`${rejectedAckCount} rejected 999 segment${rejectedAckCount === 1 ? "" : "s"} across all ack files`}
+                >
+                  {rejectedAckCount > 99 ? "99+" : rejectedAckCount}
+                </span>
+              ) : null}
             </NavLink>
           </li>
           <li>
diff --git a/src/hooks/useAckStats.test.tsx b/src/hooks/useAckStats.test.tsx
new file mode 100644
index 0000000..e7a4679
--- /dev/null
+++ b/src/hooks/useAckStats.test.tsx
@@ -0,0 +1,51 @@
+// @vitest-environment happy-dom
+(globalThis as { IS_REACT_ACT_ENVIRONMENT?: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+
+import { describe, expect, it, vi, beforeEach } from "vitest";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { renderHook, waitFor } from "@testing-library/react";
+import type { ReactNode } from "react";
+
+// Mock the API module so the hook doesn't touch the real /api/acks endpoint.
+// The mock mirrors the wire shape that listAcks returns.
+vi.mock("@/lib/api", () => ({
+  api: {
+    isConfigured: true,
+    listAcks: vi.fn().mockResolvedValue({
+      items: [],
+      total: 1161,
+      returned: 0,
+      has_more: false,
+      aggregates: { accepted: 1156, rejected: 5, received: 1161 },
+    }),
+  },
+}));
+
+import { useAckStats } from "./useAckStats";
+
+function withClient(): (props: { children: ReactNode }) => ReactNode {
+  const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+  return ({ children }) => (
+    <QueryClientProvider client={qc}>{children}</QueryClientProvider>
+  );
+}
+
+describe("useAckStats", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("returns server-computed aggregates for sidebar badge use", async () => {
+    const { result } = renderHook(() => useAckStats(), { wrapper: withClient() });
+    await waitFor(() => expect(result.current.isSuccess).toBe(true));
+    expect(result.current.data?.aggregates.rejected).toBe(5);
+    expect(result.current.data?.aggregates.accepted).toBe(1156);
+  });
+
+  it("calls listAcks with limit=1 so the lightweight payload is smallest", async () => {
+    const { api } = await import("@/lib/api");
+    renderHook(() => useAckStats(), { wrapper: withClient() });
+    await waitFor(() => expect(api.listAcks).toHaveBeenCalled());
+    expect(api.listAcks).toHaveBeenCalledWith({ limit: 1 });
+  });
+});
\ No newline at end of file
diff --git a/src/hooks/useAckStats.ts b/src/hooks/useAckStats.ts
new file mode 100644
index 0000000..19f2f7a
--- /dev/null
+++ b/src/hooks/useAckStats.ts
@@ -0,0 +1,29 @@
+import { useQuery } from "@tanstack/react-query";
+import { api, type AckAggregates } from "@/lib/api";
+
+/**
+ * Lightweight 999 ACK aggregates for sidebar / nav badges.
+ *
+ * Hits `/api/acks?limit=1` so the server-side aggregates (which are
+ * computed by iterating every persisted row) come back without
+ * pulling 100 rows for a sidebar badge. The 1-row payload is the
+ * smallest the endpoint accepts (limit ge=1).
+ *
+ * Used by the Sidebar's "999 ACKs" nav badge to surface the
+ * total rejected segment count without forcing a full page fetch.
+ * 60s stale time matches the page-level fetch cadence — the badge
+ * refreshes when the user navigates to the page anyway.
+ *
+ * Distinct from useAcks (which fetches paginated rows + aggregates
+ * for the page body). The query key intentionally differs so React
+ * Query doesn't dedupe the two into a single entry.
+ */
+export function useAckStats() {
+  return useQuery<{ aggregates: AckAggregates }>({
+    queryKey: ["acks", "stats"],
+    queryFn: () => api.listAcks({ limit: 1 }) as Promise<{ aggregates: AckAggregates }>,
+    enabled: api.isConfigured,
+    staleTime: 60_000,
+    refetchOnWindowFocus: false,
+  });
+}
\ No newline at end of file
diff --git a/src/pages/Acks.test.tsx b/src/pages/Acks.test.tsx
index a7c726e..07d31de 100644
--- a/src/pages/Acks.test.tsx
+++ b/src/pages/Acks.test.tsx
@@ -166,6 +166,69 @@ describe("Acks", () => {
     unmount();
   });
 
+  // -------------------------------------------------------------------------
+  // 2026-07-02: rejections were getting buried inside the accepted acks
+  // (1,156 accepted + 5 rejected) — the operator had to scroll the
+  // entire table to find the 5 they cared about. Fix: client-side sort
+  // bubbles rejected rows to the top of page 1. Within each group
+  // (rejected vs accepted) newest-id-first is preserved.
+  // -------------------------------------------------------------------------
+  it("test_rejected_acks_float_to_top_of_table", async () => {
+    (api.listAcks as unknown as ReturnType<typeof vi.fn>).mockResolvedValue({
+      items: [
+        {
+          id: 100,
+          sourceBatchId: "b-newest-accepted",
+          acceptedCount: 1,
+          rejectedCount: 0,
+          receivedCount: 1,
+          ackCode: "A",
+          parsedAt: "2026-07-01T12:00:00Z",
+        },
+        {
+          id: 99,
+          sourceBatchId: "b-rejected",
+          acceptedCount: 0,
+          rejectedCount: 1,
+          receivedCount: 1,
+          ackCode: "R",
+          parsedAt: "2026-07-01T11:00:00Z",
+        },
+        {
+          id: 98,
+          sourceBatchId: "b-old-accepted",
+          acceptedCount: 1,
+          rejectedCount: 0,
+          receivedCount: 1,
+          ackCode: "A",
+          parsedAt: "2026-06-25T12:00:00Z",
+        },
+      ],
+      total: 3,
+      returned: 3,
+      has_more: false,
+    });
+
+    const { unmount } = renderIntoContainer(React.createElement(Acks));
+    await waitForText("100");
+
+    // The first table row must be the rejected one (id=99), even though
+    // id=100 has a higher id. After that, accepted rows sort newest-first
+    // (id=100 before id=98).
+    const tableRows = Array.from(
+      document.querySelectorAll("table tbody tr"),
+    ).filter((row) => {
+      // Exclude any TA1-section rows by requiring the sourceBatchId
+      // pattern (TA1 rows have a different layout).
+      return row.textContent?.includes("b-");
+    });
+    expect(tableRows.length).toBe(3);
+    expect(tableRows[0]?.textContent).toContain("b-rejected");
+    expect(tableRows[1]?.textContent).toContain("b-newest-accepted");
+    expect(tableRows[2]?.textContent).toContain("b-old-accepted");
+    unmount();
+  });
+
   it("test_initial_render_shows_no_selection_highlight", async () => {
     // Three rows in the fixture so there's plenty to select; the test
     // asserts the *initial* state has no row marked selected.
diff --git a/src/pages/Acks.tsx b/src/pages/Acks.tsx
index 2a4c5e5..dff35c9 100644
--- a/src/pages/Acks.tsx
+++ b/src/pages/Acks.tsx
@@ -1,4 +1,4 @@
-import { useCallback, useState } from "react";
+import { useCallback, useMemo, useState } from "react";
 import { CheckCircle2, Download, Mail, ShieldCheck } from "lucide-react";
 import {
   Table,
@@ -63,7 +63,21 @@ export function Acks() {
   // dedupes by id (first write wins), so a snapshot replay on
   // reconnect can't double-count an existing row.
   const mergedItems = useMergedTail("acks", data?.items ?? []);
-  const items = mergedItems;
+  // Display order: rejected rows float to the top, then newest-first
+  // by id. The server returns id-DESC so accepted rows already
+  // follow that order — we only need to bubble the rejections up
+  // (the operator flagged on 2026-07-02 that 5 rejections were
+  // buried inside 1,156 accepted acks and hard to find). All 5 fit
+  // on page 1 since they're a tiny fraction of the total — the
+  // operator never needs to paginate to find them.
+  const items = useMemo(() => {
+    return [...mergedItems].sort((a, b) => {
+      const ra = a.rejectedCount > 0 ? 1 : 0;
+      const rb = b.rejectedCount > 0 ? 1 : 0;
+      if (ra !== rb) return rb - ra; // rejected first
+      return b.id - a.id;             // newest id first within each group
+    });
+  }, [mergedItems]);
   const totalCount = data?.total ?? 0;
   // Server-side aggregates — sum over the *full* ACK set, not just the
   // visible page. Without this, the KPI strip silently under-reports