Shimano Ultegra 6870 Di2 – cassette size?

Does anybody know what the biggest cassette size I can fit on the 10 speed version of this is? It’s currently fitted with standard compact chainrings and an 11 -28 cassette? I’d like to go to 30 or even 32* if I can but I have no idea if this is possible.

* I have a very long ride in the summer and I’d really like to stay out of the red zone if poss.

Do you mean 6770? 6870 is 11 speed…

I’ve fitted a 30t to my 10 speed di2, it took a bit of time to get the chain length correct, but works fine.

roadlinks are pretty cheap

My apologies you are quite right. It’s 6770. I’ll have a look at the Roadlink but I may compromise and run a 30 tooth.

Thanks very much for the help.