It is fixable, but you have to find a luthier to do the work.
The crack is there to stay.
The luthier will heavily humidify the guitar for a week or two, the seam will close, he will cleat it on the inside and he will probably put some Tight Bond into the crack itself.
It probably split on the seam of the two top pieces. Happens to a lot of guitars.
Don't use polish ever on that seam or it will discolor over time. Don't get water into the crack or it will loosen the Tight Bond glue, which is water soluble.
I've been lucky with my Martin, which is a little over three years old. I keep my house really cold in the dry winters, and that brings up the Relative Humidity in addition to humidifying the guitar in its case. (You do humidify, right?)
If it really bothers you, trade it in and get a new one, and lose a few dollars. Trouble is, guitars never stay fine, so you WILL end up trading in this one for another one's set of problems.
Martin will not cover it. However, when you go to an authorized Martin repair guy, if he likes you he may find some reason to repair it that is warranty covered.
My luthier hated the ski jump on my guitar, so he pulled on the neck a little, got to see a slight gap between the neck heel and the body, and suddenly I was entitled to a neck reset, the ski jump fix, and a new setup. We did a bunch of other stuff too and the guitar sings now and is gorgeous.
Just so you know, I got a crack on the back of mine in less than a year. Don't know how it happened, and there was no ding, and I professed humidifying, which is true, so he fixed that crack under warranty, but he had to call Martin to get it authorized. (He knows them well, used to be an Engineer there.) That's how I got to know him and then I came in for the set up later and we overhauled it, replacing dots for diamonds, squares, cat's eyes, and a compound radius fingerboard, and new frets since I had worn them down so much. (Damn Stormy Monday, all those bends when learning it forced a fret job in less than two years.) I think out of pocket everything came to under four hunder dollars. Guitar looks super cool now, but I will need new frets again in the Fall. I may have him do Stainless Steel. He can do anything!
What model is yours?
