I really feel for you, I've been there with the ASD toddler seemingly never needing to sleep. It's absolute torture and it's no wonder you're hating things right now.
If you just wanted to vent then please ignore the next bit. If you're interested in some ideas to help, then carry on.
Can I ask how long DC naps for during the day? With a wake up that early it seems like they might be better off not napping at all to add those hours onto the night.
I had a similar problem and the first thing that I did was to ban naps. It was really awful for about a week but then they got used to it. So at danger times I would make sure that we were out, stimulating environment etc. If they looked like they were drifting off in the buggy I would insist that they got out and walked. It sounds mean but it's better for both you and them to solve this problem so that they've got a better rested parent who can do more with them rather than a sleep deprived zombie.
After they got used to the no nap situation I gradually (10-15 minutes at a time) pushed back bedtime so as to extend the sleep at the other end of the night.
It might also be worth thinking about what actually wakes them up at that time. Are they cold? Need a wee? Bad dream? Hungry? If you can work it out then you might be able to remove the waking trigger. I realised that my little one was waking when he did a wee in his nappy, so I was able to limit liquids before bed and dream wee him, which let him sleep longer.
I had some limited success with the Wake to Sleep method too, it's worth a quick internet search.
Sorry for the essay, but I've spent way too long optimising sleep, as you can probably tell.
And my DC is now 5. He still wakes early but it's 5.30am rather than 4am and these days he takes himself downstairs for a bit of quiet screen time rather than waking me some days! It will get easier (eventually).