Speed has several dimensions, so lets whizz along:
Execution. In-memory architecture and distributed processing on CAS make rapid analytics web services faster than ever before.
Scalability. Whether your app has dozens, or thousands of users - SAS has load balancing and partitioning capabilities all preconfigured.
Development & Deployment. For me, this is the BEST BIT. The SAS platform has EVERYTHING you need for building a web app - the web server, enterprise authentication, application server, data storage & retrieval.. This makes it super fast to build and deploy web apps on SAS. By separating the frontend (web) and backend (SAS) the apps are also highly maintainable (standard open source javascript frameworks at frontend, regular 4GL for data queries on the SAS server).
Check out this demo of building a React Web App on SAS Viya in just 5 minutes: