diff --git a/services/api-server/src/api_server/html5.py b/services/api-server/src/api_server/html5.py
index b8f37c2..41388a4 100644
--- a/services/api-server/src/api_server/html5.py
+++ b/services/api-server/src/api_server/html5.py
@@ -1,8 +1,11 @@
 from __future__ import annotations
 
 from html import escape
+from pathlib import Path
 from urllib.parse import quote
 
+_HTML5_ASSETS_DIR = Path(__file__).resolve().parent / "static" / "html5"
+
 
 def _page(title: str, body: str) -> str:
     return f"""<!doctype html>
@@ -11,14 +14,23 @@ def _page(title: str, body: str) -> str:
   <meta charset="utf-8" />
   <meta name="viewport" content="width=device-width, initial-scale=1" />
   <title>{escape(title)}</title>
-  <link rel="stylesheet" href="/html5/assets/html5.css" />
-  <script defer src="/html5/assets/htmx.min.js"></script>
-  <script defer src="/html5/assets/htmx-ext-sse.js"></script>
+  <link rel="stylesheet" href="{_asset_url("html5.css")}" />
+  <script defer src="{_asset_url("htmx.min.js")}"></script>
+  <script defer src="{_asset_url("htmx-ext-sse.js")}"></script>
 </head>
 <body>{body}</body>
 </html>"""
 
 
+def _asset_url(filename: str) -> str:
+    asset_path = _HTML5_ASSETS_DIR / filename
+    try:
+        version = str(int(asset_path.stat().st_mtime))
+    except OSError:
+        version = "dev"
+    return f"/html5/assets/{quote(filename)}?v={version}"
+
+
 def _project_link(project: object, active_project_id: str) -> str:
     project_id = str(getattr(project, "project_id", ""))
     name = str(getattr(project, "name", project_id))
diff --git a/services/api-server/src/api_server/main.py b/services/api-server/src/api_server/main.py
index 140f141..5cc50d1 100644
--- a/services/api-server/src/api_server/main.py
+++ b/services/api-server/src/api_server/main.py
@@ -140,7 +140,7 @@ _HTML5_ASSETS_DIR = Path(__file__).resolve().parent / "static" / "html5"
 class Html5StaticFiles(StaticFiles):
     def file_response(self, *args, **kwargs):
         response = super().file_response(*args, **kwargs)
-        response.headers.setdefault("Cache-Control", "public, max-age=3600")
+        response.headers.setdefault("Cache-Control", "public, max-age=86400")
         return response
 
 
diff --git a/services/api-server/tests/test_api.py b/services/api-server/tests/test_api.py
index 74936af..7556cb4 100644
--- a/services/api-server/tests/test_api.py
+++ b/services/api-server/tests/test_api.py
@@ -35,9 +35,9 @@ def assert_html5_contract(text: str, *markers: str, full_page: bool = False) ->
     if full_page:
         assert "<!doctype html>" in text
         assert "<style>" not in text
-        assert "/html5/assets/html5.css" in text
-        assert "/html5/assets/htmx.min.js" in text
-        assert "/html5/assets/htmx-ext-sse.js" in text
+        assert re.search(r'/html5/assets/html5\.css\?v=[^"]+', text)
+        assert re.search(r'/html5/assets/htmx\.min\.js\?v=[^"]+', text)
+        assert re.search(r'/html5/assets/htmx-ext-sse\.js\?v=[^"]+', text)
     else:
         assert "<html" not in text
     for marker in markers:
@@ -152,9 +152,9 @@ def test_html5_server_rendered_project_editor(tmp_path: Path):
     assert 'hx-swap="outerHTML"' in editor.text
     assert "hx-ext=\"sse\"" in editor.text
     assert f"sse-connect=\"/html5/projects/{project_id}/events\"" in editor.text
-    assert '/html5/assets/html5.css' in editor.text
-    assert '/html5/assets/htmx.min.js' in editor.text
-    assert '/html5/assets/htmx-ext-sse.js' in editor.text
+    assert re.search(r'/html5/assets/html5\.css\?v=[^"]+', editor.text)
+    assert re.search(r'/html5/assets/htmx\.min\.js\?v=[^"]+', editor.text)
+    assert re.search(r'/html5/assets/htmx-ext-sse\.js\?v=[^"]+', editor.text)
     assert "unpkg.com" not in editor.text
     assert "client-js: htmx+sse only" in editor.text
     css = client.get("/html5/assets/html5.css")
@@ -257,17 +257,17 @@ def test_html5_server_rendered_project_editor(tmp_path: Path):
     htmx_asset = client.get("/html5/assets/htmx.min.js")
     assert htmx_asset.status_code == 200
     assert "javascript" in htmx_asset.headers["content-type"]
-    assert htmx_asset.headers["cache-control"] == "public, max-age=3600"
+    assert htmx_asset.headers["cache-control"] == "public, max-age=86400"
     assert "htmx" in htmx_asset.text
     sse_asset = client.get("/html5/assets/htmx-ext-sse.js")
     assert sse_asset.status_code == 200
     assert "javascript" in sse_asset.headers["content-type"]
-    assert sse_asset.headers["cache-control"] == "public, max-age=3600"
+    assert sse_asset.headers["cache-control"] == "public, max-age=86400"
     assert "sse" in sse_asset.text
     css_asset = client.get("/html5/assets/html5.css")
     assert css_asset.status_code == 200
     assert "text/css" in css_asset.headers["content-type"]
-    assert css_asset.headers["cache-control"] == "public, max-age=3600"
+    assert css_asset.headers["cache-control"] == "public, max-age=86400"
     assert ".workspace" in css_asset.text
 
 
