What's up with the Xfinity Speed test?

Your explanation does not make sense. I did a tracert to speedtest.xfinity.com and it goes from my modem to the Beaverton Headend, across Xfinity's system only (Internet not involved), and I get 20-150 mbps out of my provisioned 400 mpbs. However, when I do a speed test from an Internet web site I get 400mbps (plus or minus 5%) Since the internet speed tests has the same path to the headend as the Xfinity speed test (po-112-rur102.troutdale.or.bverton.comcast.net to  ae-52-ar01.troutdale.or.bverton.comcast.net) before the packets go out to the Internet, the Xfinity speed test should be much, much, faster, but it isn't. 

Mind you I'm not complaining. I am satisfied that I'm getting what I am paying for, especially since I am getting ten times the upload I was expecting. It's just that the tool that you provide should be reflecting reality, and it isn't. When I run the app or do the test at speedtest.xfinity.com, it wants me to schedule a tech trouble call, because it says I'm not getting the speed I'm paying for.

That is specifically for Wifi speed testing. If you use a hardwired connection, that would provide a more accurate speed as long as your testing from a device that is capable of supporting your full speeds. Since other factors may impact the speed when using Wifi, but no worries. If you could send our team a direct message with your full name, the name listed on the account (if different), and the service address associated with your account, I'd be more than happy to look into this for you. To send a Direct Message, please click on the chat icon in the top-right corner of the screen, next to the bell icon, and then type or select "Xfinity Support" to initiate a direct message. 

Neither you nor your teammate prior are even reading what OP stated in the initial post. That’s precisely why customers get so irritated, and give Xfinity such a bad rep. We all appreciate you taking the time to reply, but please, at least ensure you’re actually responding with worthwhile info. That info helps this OP, and others finding this thread. 

I found the issue. It is Xfinity's servers that run the speed test. Using the speed test app from Ookla, I discovered that if I run the speed test to Century Link's servers, or Boost Wireless's servers, both of which are 6 miles away I get nearly 500mbps, (I am provisioned for only 400), While if I select any of Xfinity/Comcast's servers, the nearest one of which is also 6 miles away I consistently get between 20 mbps and 150 mbps.  Those are the servers that the Xfinity speed test connects to. Since the Xfinity test is between my modem and the headend in Troutdale OR (6 mi away) and the test is on Xfinity's plant only, while the other tests cross the same plant and then the internet, the fact that the Xfinity test is so slow makes me wonder if it is rigged to make customers think that they need a service call. 

I thank God I'm a retired Xfinity technician and I can weed out the [Edited: language] that you noticed from XfinitySeth and XfinityAmandaB.  I just hope that they take to heart the troubleshooting that I did to point to their server issue, but I'm not keeping my hopes up. And yes, when I was a tech I did run into these "experts" too. It was frustrating. Sometimes I wanted to scream, "did you listen to me." I remember I went four times to a customer who couldn't make calls to a certain area of Canada and I couldn't get people to believe me that it wasn't a problem in the customers house.

Above all, I'm glad your speeds are coming in how they're supposed to 👍 In your original post, you asked why the Xfinity apps speed test results may differ from other speed tests you've run, and the information provided in my original comment was to inform you exactly why that is. We appreciate your feedback and are happy to continue helping at any time if you feel your services are not performing as needed, but otherwise I hope you have a great rest of your holiday weekend 🙌