Unable to get IPv6 address

I’m seeing mixed information on whether SMARTY/Three provides IPv6, so I’m hoping someone can clarify.

I’m using a 4G/LTE router (not a phone). The router supports IPv6 and is configured for dual-stack (IPv4/IPv6) with IPv6 auto-config enabled, and I’ve also tried requesting prefix delegation. The SIM connects fine for IPv4, but the WAN interface only ever shows a link-local IPv6 address (fe80::…), never a global IPv6 address or delegated prefix.

APN in use is three.co.uk.

Does SMARTY currently provide IPv6 for data connections, and if so:

is it available on all plans/SIMs, or only certain ones?
is there a specific APN or setting required to get IPv6 working on routers?
do you support IPv6 prefix delegation for LTE routers?

Any guidance appreciated. Thanks in advance.