diff --git a/app/main.py b/app/main.py
index 285260d..ee9e700 100644
--- a/app/main.py
+++ b/app/main.py
@@ -159,6 +159,30 @@ async def api_revoke_key(name: str, request: Request):
         return JSONResponse({"error": e.detail}, status_code=e.status_code)
 
 
+@app.get("/api/matrix-mxid")
+async def api_get_matrix_mxid(request: Request):
+    identity = get_user_identity(request)
+    if not identity:
+        return JSONResponse({"error": "unauthenticated"}, status_code=401)
+    try:
+        return await broker_get(identity, "/broker/matrix-mxid")
+    except HTTPException as e:
+        return JSONResponse({"error": e.detail}, status_code=e.status_code)
+
+
+@app.post("/api/matrix-mxid")
+async def api_set_matrix_mxid(request: Request):
+    identity = get_user_identity(request)
+    if not identity:
+        return JSONResponse({"error": "unauthenticated"}, status_code=401)
+    body = await request.json()
+    mxid = (body.get("matrix_mxid") or "").strip()
+    try:
+        return await broker_post(identity, "/broker/matrix-mxid", {"matrix_mxid": mxid})
+    except HTTPException as e:
+        return JSONResponse({"error": e.detail}, status_code=e.status_code)
+
+
 # ---------------------------------------------------------------------------
 # OIDC routes — authorization-code flow against Cloudron's OIDC provider.
 # Active only when the `oidc` addon is configured (CLOUDRON_OIDC_* present).
@@ -532,6 +556,16 @@ PAGE_HTML = """<!DOCTYPE html>
       <button class="ghost" onclick="$('key-reveal').style.display='none';">Dismiss</button>
     </div>
   </div>
+
+  <div class="card">
+    <h2>Matrix chat</h2>
+    <p class="hint">You're invited to the co-op's Matrix space at your co-op account (<code id="local-mxid">@you:inference.coop</code>). Prefer to use an existing account on another server instead? Add it below (one account).</p>
+    <div class="new-key">
+      <input id="mxid-input" type="text" placeholder="e.g. @you:matrix.org" maxlength="255" />
+      <button class="primary" id="mxid-btn" onclick="saveMxid()">Save</button>
+    </div>
+    <div class="hint" id="mxid-status"></div>
+  </div>
 </div>
 
 <footer>
@@ -594,11 +628,48 @@ async function load() {
     renderModels(d.models || []);
     renderBoard(d.coop_models || []);
     renderKeys(d.keys || []);
+    loadMxid();
   } catch (e) {
     flash('Could not load usage: ' + e.message, false);
   }
 }
 
+async function loadMxid() {
+  try {
+    const r = await fetch('/api/matrix-mxid');
+    if (r.status === 401) return;
+    const d = await r.json();
+    if (d.error) return;
+    if (d.local_mxid) $('local-mxid').textContent = d.local_mxid;
+    if (d.matrix_mxid) {
+      $('mxid-input').value = d.matrix_mxid;
+      $('mxid-status').textContent = 'Using ' + d.matrix_mxid + ' for Matrix invites.';
+    }
+  } catch (e) { /* non-critical */ }
+}
+
+async function saveMxid() {
+  const mxid = $('mxid-input').value.trim();
+  const btn = $('mxid-btn');
+  btn.disabled = true;
+  $('mxid-status').textContent = '';
+  try {
+    const r = await fetch('/api/matrix-mxid', {
+      method: 'POST', headers: {'Content-Type': 'application/json'},
+      body: JSON.stringify({ matrix_mxid: mxid })
+    });
+    const d = await r.json();
+    if (d.error) { $('mxid-status').textContent = d.error; }
+    else if (mxid) {
+      $('mxid-status').textContent = 'Saved — invitations will go to ' + mxid + '.';
+    } else {
+      $('mxid-status').textContent = 'Cleared — your co-op account will be used for Matrix.';
+      $('mxid-input').value = '';
+    }
+  } catch (e) { $('mxid-status').textContent = 'Could not save: ' + e.message; }
+  btn.disabled = false;
+}
+
 function renderModels(models) {
   const el = $('models');
   if (!models.length) { el.innerHTML = ''; return; }