For anyone else coming to this much later on, you can enable GlideAjax in your direct UI Pages by including the UI Script which initiates GlideAjax.

Include this HTML in the top of your UI Page template

<script type="text/javascript" src="/scripts/doctype/js_includes_doctype.jsx?v=09-08-2025_1328&amp;lp=Wed_Sep_17_06_56_19_PDT_2025&amp;c=13_273"></script>

I found this by looking at a UI Page with Direct=false and then using browser dev tools to search the sources for "GlideAjax =". Not a bullet proof way to find things, but it also helped me find the script for amb client.