I asume you mean the 960 pro.  I doubt you mean 850 as that's a sata not nvme interface.

Nice to know it fits though, I ordered one only to realize I never checked to see if the helix 2 took an 80mm long card or if I needed to find a shorter one :P

Nope, just tested Samsung 960 evo on helix 2. Windows will install but bios can't boot it. Helix 2 motherboard won't boot nvme drives. Use 850 evo as it's sata interface instead. 

FYI the pro might work. Some people say the pro inserts it's own firmware during boot time to enable older machines to boot it, didn't have a pro unit to test.

Gandalforce's method worked for my NVME.  I don't recall what model mine is.  I'll have to check when I get home.

I have the 950 pro 256gb.

Thread revive!

Mine is the Samsung 950 Pro. NVMe style for a PCIe connection. M.2 size.

Been working for 2 years now, soild performance but the Core M 5Y71 bottlenecks on clock speed.

It works guys, trust me. 

Thanks! I have an OEM 950 Pro running in my X1 Tablet (SM951 MZVKV512HAJH) and am tempted to swap it into the Helix 2 to breathe some new life into it. Would that be a similar part number to yours? I have tried a PM951 part but that would not boot on the Helix 2.

Mine is a retail 950 pro.  I don't think I had any luck with the SM951 and ended up swapping it out with a retail 950 pro from work.  I have a horrible memory though so don't stop it from exploring it as an option.

Thank you for the update. I find it amazing that the Helix 2 is only a 2015 machine and it seems crippled in all sorts of ways already. Perhaps this would help.

So based on everyones testing so far and my own research, the helix 2 does not support nvme devices for booting, only sata which means the nvme evo devices won't work.  However it appears retail pro devices do work. If anyone who is using a pro device can test this, could you see if the pro is loading it's own firmware on boot?  This would explain it working. A classic example of this is raid controllers and some network cards, how during the boot process they'll load their own firmware to allow the device to function on computers who's bios don't support booting from raid/network.

If this is the case, I kinda wish I bought a pro instead of the evo I tried lol.

Anyway, starting a list of known compatable devices for helix 2.

SSD;  

Any m.2 sata card

samsung 950 pro nvme retail card [must be retail version of pro]

wwan cards.

Helix 2 ships with a range of cards, for those who are unlucky like me and got a sierra em7345 card which is a buggy extremely unreliable card that only worked 40% of the time. Lucky unlike past lenovo products, the helix 2 isn't locked down to a specific card.  I installed the sierra em7455 card and haven't had a problem since, had to make a gps antenna though. Please note, after installing any card, even if windows recognizes it from the start, it won't work till you install official driver package and/or your carriers firmware. till then it'll claim there's no sim installed.

known wwan cards to work well;

sierra em7455

Known not working devices

Sierra EM7345 works 40% of the time, and what's pathetic is this is the primary card they ship in the helix 2. in fact avoid any wwan card that's based on intel chipsets, none of them work reliably at this point. qualcom based devices work great.

Samsung nvme evo devices. Helix 2 can't boot nvme devices without a little help, some devices load their own firmware at boot to bypass older bios limitations.