The rotation question gets asked constantly and answered anecdotally, usually with whichever handful of assets the speaker happens to hold. This compresses it into a single reading: over the period being measured, is the wider field beating Bitcoin or losing to it.

A season on this reading is a condition that has persisted, not a day that happened to go one way. That distinction is what makes the reading worth tracking over months rather than reacting to each week.

What it actually measures

The reading is relative from end to end. A field beating Bitcoin through a general decline counts exactly the same here as a field beating Bitcoin through a general advance, because the only comparison being made is between the two sides.

These states have lasted months rather than days, which is what makes the reading worth following at all. Single-week swings around the trend are the ordinary texture of the series rather than turns in it, and treating each one as a change of season produces a considerable amount of activity and very little information.

The measurement window decides what counts as a season in the first place. A shorter one flips far more often and describes something closer to this month, which is a legitimate question and a different one.

Underperforming and falling are different claims

A reading favouring Bitcoin gets heard as alts going down, which is a reasonable-sounding inference and frequently wrong. It says they are gaining less, which is compatible with them gaining a great deal.

The confusion matters because it changes what the reading is good for entirely. Anyone taking a relative statement as an absolute one has been told nothing whatever about direction while believing they have been told the most important thing.

BTC vs Field: an average return conceals the thing worth knowing

The spread is the reading. A tight fan says the market moved as one, so exposure mattered more than selection; a wide one says the opposite, and says it emphatically enough that the difference between two names dwarfed the difference between being in and being out.

Summary statistics about a market describe an asset that nobody actually owns. The average return over a period is a perfectly real number about an entirely imaginary holding.

The spread is what a real holder actually faced: a range of outcomes wide enough that the choice between two names mattered a great deal more than the direction of the market did. A fan makes that visible immediately, and an average makes it disappear completely.

What it does not tell you

It is a summary of a very large question. Which assets are counted, over what period, and weighted in what way are all choices, and other perfectly defensible choices would give materially different answers.

It says nothing whatever about why capital is moving. Rotation happens for reasons of policy, of narrative and of plain fashion, and none of them are visible in this reading.

Persistence is a historical tendency rather than a rule. The current state has ended abruptly before, without anything in the reading having warned of it.

It treats the field as one thing. A season can be under way for half the market and entirely absent from the rest, and a single reading cannot show that.

How to read it

Altcoin season. Money is moving outward, away from Bitcoin and into the rest.

Neutral. No decisive rotation in either direction.

Bitcoin season. Capital is concentrating into Bitcoin.

Alt Season Index is one of the views on the Relative Performance dashboard, along with BTC Dominance, Altcoin Breadth and BTC vs Field.

Common questions

When does a stretch become a season?

A sustained majority of the field either beating Bitcoin or failing to, across the period being measured. It names a condition that has held rather than a day that happened.

Must the others fall for Bitcoin to win?

Not necessarily. It means they gain less, which can happen while everything is rising. Relative and absolute are separate questions.

How quickly do these change?

Slowly, on the record so far: these conditions have held for months at a stretch, and so the reading repays following. A single week going the other way is generally the series wobbling rather than turning.

How much does the measurement window matter?

Considerably. A shorter one flips more often and describes something closer to this month than to a season, which is a different question.

What does it not explain?

Why the rotation is happening. The reading records where capital is going and has nothing to say about what sent it there.

Why rebase everything to one start?

So the eye is not misled. Once every line begins in the same place, the gap between any two of them is the genuine difference in how they did, rather than an artefact of what each one costs.

Does it show what each asset cost to hold?

No. This is a performance picture, and nothing about the falls endured along the way appears in it.