Over at the forums, the word is spreading that the team AOSParadox is working on the Marshmallow AOSP ROM for the last year’s dashing OnePlus One set. A working build isn’t available as of now, so you have to wait — and pray, perhaps — for it to happen.
We has heard the gossips earlier that AOSPA Marshmallow ROM are in being worked on, and it’s great to hear that it’s now happening for the cool device OnePlus One is.
You will need Marshmallow Gapps with this ROM because it’s an AOSP based ROM, and thus won’t have Google Apps (Gapps) by default installed.
Once the ROM is available for download, we will let you know. Be sure to check back here as we will be updating the post with latest developments.
Via OnePlus Forums