The upgrade treadmill is planned obsolescence applied to the human body. Each enhancement generation is designed to integrate so deeply with cognitive and biological systems that removal becomes more dangerous than continuation. You're not paying for an upgrade — you're paying to not be downgraded, because baseline human capability now feels like a disability after a year of enhancement.
The mechanism mirrors the SaaS model: your body runs on subscriptions. Neural processing, sensory enhancement, immune system optimization, metabolic regulation — all licensed, all versioned, all requiring periodic updates that introduce new dependencies. Each upgrade makes the previous version feel intolerable. Each new dependency makes the subscription non-optional. The person who chose to enhance their vision five years ago now literally cannot read without the current-generation optic suite — not because their natural eyes were damaged, but because their brain rewired around the enhanced input and can no longer process unaugmented visual data.
The Great Divergence (ST #9) describes the outcome — society split into haves and have-nots. The Upgrade Treadmill is the mechanism — the engine that makes the split irreversible. Those who step onto the treadmill can never step off without catastrophic capability loss. Those who never step on become increasingly unable to participate in a society designed for the enhanced. Both groups are trapped. The only people who profit are the ones selling the next version.
But the chrome was never the only carrier, and arguably never the point. Strip the augmentation away and the same engine remains: a function you cannot perform yourself, outsourced to a system you cannot fully maintain, sourced from a market that prices your desperation rather than the part's value, degrading at a rate you systematically underestimate. This is the Salvage Spiral — the treadmill running on physical survival hardware instead of neural firmware. A Rail Runner who has never taken an augmentation is on the treadmill the instant they buy a crawler, because the crawler is a dependency they cannot build, cannot audit, and cannot finish paying for: drive modules dying every nine weeks at 340% markup with no manufacturer, hardshells degrading invisibly until the threshold, power taps whose green lights mean circuit closed, not circuit useful. Where the firmware treadmill has a designer — leaked specs pegging integration to billing cycles — the Salvage Spiral has only a corporation that walked away from the market and entropy doing the rest. The engineered treadmill is the special case. The salvage treadmill is the natural one, and its purest prisoners are the unaugmented poor the body-subscription story was supposed to leave alone. The terminus of both is the same: the Convergence Crown, the upgrade that has restructured its wearer so completely that removal is no longer survivable.