Cox did not start as a product.
It started as a coach for a single athlete — and it has run there every day since June 2025: load, recovery, weekly planning, nutrition, race preparation. What becomes public arrives piece by piece. Strength and nutrition are first.
The athlete first, the product after
The engine grew around a person who trains with it every day: a briefing in the morning, a debrief in the evening, the week on Sunday, and planning across months in between. Every rule in it is there because a real training year demanded it — not because it looks good on a feature list.
That is the difference you can see in software the moment things get awkward: what happens on the day the sleep was bad, the session was missed, and a race is still coming closer? Those cases are not hypothetical here. They happened.
The day as the coach sees it. Example data.
The engine is the part that stays
Language models change — several times in the last year, and the next change is certain. What a model phrases is replaceable. What calculates is not: load and recovery, volume per muscle group, progression per exercise, the shape of the week.
That is where the work sits. The model receives the result and puts it into sentences; it is not given the job of inventing a plan. Turn that around and you have a product that answers differently every Tuesday.
The week, added up. Example data.
What is open today.
What you get in the closed beta — in full, not as a preview.
Strength
Gym mode on the iPhone, progression per machine, 343 exercises with a movement clip, twenty ready-made plans, analysis across muscle groups and weeks. The way in, and the most built-out part.
Nutrition
A photo of the label or of the plate, barcodes, your own food list. Balance against your measured expenditure, protein across the day, carbs around the hard session.
The coach
Briefing, debrief, weekly report, signals — with memory across months and a brake in front of it. In the app, in the browser and, if you want, in Telegram.
Body
Weight, girths and composition — by hand or from the scale, shown as the trend rather than the daily wobble. Your own entry beats any device.
Your devices
intervals.icu (and with it Garmin), Withings, Apple Health, a heart-rate belt in the gym, FIT files by hand. Without a device Cox still calculates — then what you report yourself is what counts.
Your data
Export and deletion are features, not favours: you delete your account yourself, and the connected data sources are deregistered in the process.
What sits on the platform and is not open yet.
The modules exist, they can be switched on per account, and the personal coach uses them daily. They are not public yet — here is which.
Endurance: running, cycling, swimming, triathlon
Where all of this came from. The load arithmetic for it already runs today — if you run or ride alongside the gym, your strength plan knows. What is missing is the surface for it: weekly planning, zones, pace and power models.
Races
A race in the calendar changes everything before it: the build, the unloading, peaking on one day. In the personal coach that is the part with the most rules — and the one that fits a pure strength app least.
Consistency goals
Not "seven-day streak", but goals that survive a bad week: how many sessions, how regularly, across what period — measured against what you set yourself.
Bloodwork and journal
Both deliberately restrained: bloodwork is displayed and not interpreted, and the journal is the part nobody but you reads. Cox is a wellness companion for your training — not medical advice.
We name a date for none of it, and that is deliberate: a module comes out when it is clean for other people's accounts — not when a calendar says so.
Why it comes piece by piece.
A coach for one person is allowed things a service for many is not. That gap is exactly the work between the one and the other.
- Every query belongs to exactly one account. In the personal coach the athlete was a constant in the code; here he is a parameter, and the database additionally enforces that nobody can see another account's rows.
- Personal thresholds become yours. What was calibrated there for one human — load thresholds, care for a sensitive back — is a profile here that you fill in yourself, with defaults for everyone else.
- Time zones, language, units. A coach for one person knows one time zone. A service writes to you at seven in the morning in yours.
- And what shouldn't come along, doesn't. No supplement module, blood pressure for display only, no interpretation of your values. Some of what the personal coach does deliberately does not belong in a product.
That is also the answer to why the beta is closed: every new account is the test of whether that separation holds.
Strength and nutrition are open.
The rest follows once it is clean for other people's accounts. Leave your address and you'll hear about it first.