Geforce gtx 1080 3 & 4

According to PCPerspective, Nvidia will only allow 3 & 4-way SLI on GeForce GTX 1080 and GTX 1070 in certain situations like synthetic benchmarks and some old games.

Nvidia will only allow 3 & 4-way SLI in very specific scenarios

If you intend to build a team with more than two Pascal-based graphics cards, you should reconsider your approach since Nvidia is going to seriously limit SLI configurations with more than two cards. Nvidia has changed its multi-GPU configuration policy with Pascal and has introduced the 'enthusiast key' concept which consists of nothing more or less than allowing the use of 3 & 4-way SLI configurations in a very small number of selected video games and in the synthetic benchmarks. A limitation that will come via drivers so little can be done to avoid it.

We do not really know what has led Nvidia to make this decision with the arrival of Pascal, although it is true that configurations of three or more cards provide a much lower performance scale than with two cards, but we do not believe that this is a reason for limit the freedom of users, after all pay cards with their money.

The decision that AMD will make with CrossFire technology in its new Polaris cards remains to be seen, hopefully it will not take the same path as Nvidia.

Source: videocardz