There is a recurring story about the Sennheiser HD 600 that does not get told often enough: the headphone has been in continuous production, with effectively the same drivers and the same chassis, since 1997. In a category whose business model depends on annual refreshes, planned obsolescence, and the suggestion that last year's reference is now ten percent obsolete, this is, to put it mildly, a structural anomaly.
It is also why the HD 600 keeps winning.
"Every audio category eventually finds its reference object. The HD 600 has been ours for so long we forgot to be surprised about it."
Almost every serious headphone released in the last twenty years has been benchmarked, implicitly or explicitly, against the HD 600. Reviewers describe new releases as "more analytical than the HD 600," or "warmer than the HD 600," or "with the soundstage the HD 600 has always lacked." This is the language of a fixed point. You do not use a moving object as the unit of measurement.
The honest case for not buying anything else
The HD 600 is not the best headphone you can buy in 2026. There are objectively better headphones. Planar magnetics with more resolution, closed-backs with better isolation, wireless with conveniences the HD 600 will never offer. None of them will still be in production in 2055. None of them will have a thriving aftermarket of replacement parts, foam, cables, and modifications a quarter-century after release. None of them are reference objects.
If you are going to own one good pair of headphones for the rest of your listening life, the HD 600 is the answer you can stop researching. That is the entire game.