Full Answer

Tag Gateway operates at the script-delivery layer. It proxies gtag.js and the Google collection endpoint through your own domain, which reclassifies measurement cookies from third-party to first-party. Safari and Firefox no longer cap them at 7 days, so GA4 can stitch returning-visitor sessions that would otherwise break. Setup takes minutes in Google Ads or GA4, costs nothing to host, and requires no server management. The trade-off is scope: Tag Gateway only covers Google properties — it cannot forward events to Meta, TikTok, or any non-Google destination.

Server-side GTM sits at the event-processing layer. A container running on Cloud Run or a similar host receives events from your site, enriches them with server-side logic, and routes them to any tag vendor. That flexibility is what drives the $70,000–$145,000 five-year cost — Cloud Run hosting, developer time for container maintenance, and the operational overhead of keeping vendor tags updated. For stores that advertise across multiple platforms, that cost buys multi-channel conversion data that Tag Gateway cannot provide.

Most WooCommerce stores benefit from running both. Tag Gateway fixes the Google cookie problem for free; server-side GTM handles everything else. For the full breakdown, see [Google Tag Gateway vs Server-Side GTM for WooCommerce — One Simplifies, One Controls, Neither Replaces a Tracking Plugin](https://seresa.io/blog/google-tag-gateway/google-tag-gateway-vs-server-side-gtm-for-woocommerce-which-one-do-you-need).