Early versions of the 11 speed durace had problems with the supporting spider breaking. I presume this is what happened here.
Shimano may warrant this, but really you got your normal miles out of it anyways.

The latest generations of DA cassettes do not have the best reputation - usually it's the carbon carrier that breaks, though. I had one starting making squeaking noises in the largest cogs last year and changed it out knowing their history. I'd stick with Ultegra - or go SRAM Red if you want something fancy or their (IMO) better gear ratios.

Thanks for the useful comments.. I ended up replacing it with an 11-28 Ultegra cassette.

Was it a DA 9000 cassette? As others have said, there are known issues with the carbon carriers creaking/breaking. Take a look at this article and see if your one is the same model:

https://bikerumor.com/...-eliminate-creaking/

I don't know if Shimano openly acknowledge there is/was an issue now, but you might be lucky and get a warranty replacement.

Yes, that's it... with the single rivet design as shown in the article.

Yup. Super common as said above. It's basically a foregone conclusion on those models. Good news: send it to Shimano warranty replacement and they've seen so many of them that they'll get you a replacement within a couple days.

So, not to hijack the thread, but is it typical for a cassette to last 9000 miles/3 years? I must be a sucker -- I was told that the cassette should be replaced at the same time as the chain, every 3000 miles or so, or whenever the chain shows significant wear (stretch), so that's what I've always done.

I change cassettes with every other chain. 3k per chain, so roughly 6k for a cassette. A bit more for my Campy stuff.

It says a lot about the manufacturing and material marginal gains over the last 20 years to be reading this thread.. we used to pay hundreds of $$ for aluminum freewheels that might last 5-6 road races.. same for super light rims. At most, this stuff lasted a season.. of racing only. Train on steel, race on Ti..

This design suffered from the failure mentioned above, essentially the pins rub a little counterbore on the outer face of the titanium cog and over time a stress fracture develops that connects to the rivet, it's as much a result of how narrow the spacing has become relative to the advancement in chains technology as anything else. Shimano have improved 'fixed' it in newer generations, but realistically 9000 miles from a Ti cassette is way beyond expectation.. or at least way beyond traditional expectations.

AndyCaleb is generally right, the chain and cassette should be replaced ~3k miles, mainly to keep the chain from wearing out the chainrings resulting in a far more expensive replacement.. but to let it go at 9k and replace the whole lot probably isn't bad! Either way, it's important to remember how good this stuff is nowadays.. half the weight, lasts 4 times as long and works 10x better, everything fails eventually and I think you can say that you ultimately got your money's worth out of this one!

Josh

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Modern Dura-Ace cassettes use steel for most of the cogs, and are intended to be a decently long-lasting part. They're not a race-day-only item in the same way that the short-lasting aluminum freewheels of old were a race-day-only item.

The closest thing to a modern equivalent to the old-school aluminum freewheel cogs would be a modern aluminum cassette, like the Recon ones. Those are much lighter than Dura-Ace cassettes.