Walls and Ceilings - Ceiling crack repair help needed

We are going to paint the interior of our home and have a nasty ceiling crack that needs repair. The crack in is the high ceiling of our 1962 split level home. It is about five feet long and runs to the entry light that hang from the ceiling.
I do not want to mud and tape it it wouldn't look against the 40+ year stipple of the many coats of paint.
What I am hoping is that there is some sort of flexible spackle or caulk that I can use to fill the gap which is 1/8" wide or less. I am not trying to miraculously make the crack disappear, but am shooting to eliminate the "dark valley" that the crack makes.
Any ideas?

You may be able to caulk it. The best way to fix it is with tape and mud. You can eliminate the slick finish of the repair by thinning down som mud and texturing with a sponge. Trial and error will get you a matching repair.

Thanks. I had contemplated using caulk.
Would the best caulk for this application be basic paintable latex interior caulk?
Is there such a thing as flexible spackle?