https://archiveofourown.org/works/13272 ... s/30368139
It's Megatron/Optimus Prime...and while it's explicit also features poetry and has subtextual referencing of Ursula Le Guin's The Ones Who Walk Away From Omelas. So yes. Classy robot pr0n.
This is written by astolat aka Naomi Novik who is a Locus award-winning and New York Times bestselling author. She's a hugely prolific fanfic writer, one of the founders of AO3 (probably the best and well-known fanfic archive on the internet), and has work that is enjoyable even when you know nothing about the fandom. XD (Case in point: I haven't actually watched any of the Transformers movies.)
She's known for her Temeraire series - which I enjoyed the first book of, but have very Complicated Feelings about the second book (and hence stopped reading the series). But I do have her fairytale reworking novels Uprooted and Spinning Silver on my to be read list.
She's also the writer of my FAVOURITE FIC IN THE (bbc) MERLIN FANDOM:
https://archiveofourown.org/works/40561 Crown of the Summer Court.
(It's Arthur/Merlin and so lush and beautifully written <3 <3)