From Goodreads

The Long Cosmos (The Long Earth #5)
by Terry Pratchett, Stephen Baxter
3.85 · Rating details · 4,533 Ratings · 399 Reviews
2070-71. Nearly six decades after Step Day and in the Long Earth, the new Next post-human society continues to evolve.

For Joshua Valienté, now in his late sixties, it is time to take one last solo journey into the High Meggers: an adventure that turns into a disaster. Alone and facing death, his only hope of salvation lies with a group of trolls. But as Joshua confronts his mortality, the Long Earth receives a signal from the stars. A signal that is picked up by radio astronomers but also in more abstract ways – by the trolls and by the Great Traversers. Its message is simple but ts implications are enormous:

JOIN US.

The super-smart Next realise that the Message contains instructions on how to develop an immense artificial intelligence but to build it they have to seek help from throughout the industrious worlds of mankind. Bit by bit, byte by byte, they assemble a computer the size of a continent – a device that will alter the Long Earth’s place within the cosmos and reveal the ultimate, life-affirming goal of those who sent the Message. Its impact will be felt by and resonate with all – mankind and other species, young and old, communities and individuals – who inhabit the Long Earths…

The Long Cosmos by Terry Pratchett
My rating: 3 of 5 stars

FINISHED!!! What a saga. I have enjoyed it immensely, but at the end, I think the authors were just tired with it all. It seems to just run out of steam. Some great ideas in the early books but just a bit ho-hum towards the end. Most of the characters were sorted out and certainly not a Game of Thrones pogrom. While essential reading for SciFi lovers,it would have been good to have finished with more options. Oh well. Thanks, Terry – hope you enjoy the Cosmos.