I haven't checked imbibe, but I just checked Mr. Boston and DeGroffs new book and both list it as 1:1:1 (with mr. boston adding a splash of club as optional) stired over rocks.
Interestingly, the history states that I was wrong, it was invented in 1925. still checking when it first appeared in print though.
p.s. the general consensus for shaking or stirring is that either produces an equally cold drink (although still brings up thermodynamics debate, but...i'll debate that with the everchanging variable of ice in size, shape, temp, hardness, etc.) however, usually for aesthetics, you stir most cocktails that are "clear" meaning they don't have cloudy fruit juices. i.e. a manhattan, martini, etc. and you usually shake anything with fruit juice....usually. in most cases..........for the most part....with exceptions of course.
remember, the most important ingredient in a cocktail, especially a Martini, is water (from dilution of ice)