IPv6 Network nexthop

Ok good news and bad new. I know this is doable, I found another user who has what I want setup.
He was lucky and actually had a comcast member respond after he posted on Reddit.  I reach out to the support team but I have a feeling they aren't yet accustom to IPv6 routing requests.

I also see a similar request below that has been resolved, I basically need the same thing:

https://forums.businesshelp.comcast.com/t5/IPV6/IPv6-routing-on-DPC3941B-in-pass-through-mode/td-p/39664

Fingers crossed.

Hi, @smoats! Thanks for reaching out to Comcast over our Forums page. You have reached the Digital Care team and we will be happy to help! You can enable IPv6 routing and make sure that you have LAN IPv6 Address Assignment set as Stateful. If you continue to have issues, please click on my handle (Comcast_Gabe) and send a private message with your name, the complete service address (including city, state, ZIP, suite number, etc), and the phone or account number.

Good luck.

I spent a long time trying to get the modem to consistently route IPv6 traffic to hosts behind a router using prefix delegation and it works but only for (almost exactly) 48 hours at a time.  So now I have a script that reboots the modem whenever it stops routing traffic.

Customer service was friendly but ultimately did not resolve my issues.

Progress!
I've been able to get dynamic IPv6 allocations to work but there now seems to be a firewall between me and the internet. Outbound ICMP/TCP is fine, inbound isn't.

Does Comcast block inbound connections via IPv6?

That is a great question! We don't block IPv6 connections, inbound or outbound. I would love to help you with finding a solution and getting everything working for you. Please click on my handle "ComcastBillie" and send us a private message with your full name and address to get started.

By default, the modem's firewall is blocking inbound IPv6. To disable this, log into the modem as "cusadmin", and in the left menu click on:

Firewall -> IPv6 -> Select "Custom Security" -> Select "Disable entire firewall". (there are a few other options if you would like some limited filtering).