Fallout 4's Survival Mode is now available as part of the 1.5 beta update, accessed on Steam by opting in to the beta test. But how do you go about accessing it?
1. Log into Steam
2. Right Click on Fallout 4 in your Library
3. Select Settings
4. Select Betas
5. A drop down menu will appear. Select Survival Beta Update
6. Select OK
7. Wait a few minutes and Fallout 4 should update
8. When done, Fallout 4 should appear as Fallout 4 [Beta] in your Library
This update will be available on consoles next month, with further details about the new mode available here.