Found the description of the change in the release note: https://github.com/pytorch/pytorch/releases/tag/v1.5.0 4.
But even with torch._C._jit_set_profiling_mode(True), I don’t see any fusion group in the output.
$ cat small.py
import torch
torch._C._jit_set_profiling_mode(True)

def f(x,y): return x + y * 3

print(torch.jit.script(f).graph_for(torch.rand(2, 2, device='cuda'), torch.rand(2, 2, device='cuda')))

$ python small.py
graph(%x.1 : Tensor,
      %y.1 : Tensor):
  %2 : int = prim::Constant[value=3]() # small.py:4:27
  %3 : int = prim::Constant[value=1]()
  %4 : Tensor = prim::profile(%y.1)
  %5 : Tensor = aten::mul(%4, %2) # small.py:4:23
  %6 : Tensor = prim::profile(%x.1)
  %7 : Tensor = prim::profile(%5)
  %8 : Tensor = aten::add(%6, %7, %3) # small.py:4:19
  %9 : Tensor = prim::profile(%8)
   = prim::profile()
  return (%9)