Carriage and the free-ride index

Bought or riding: why bytes a token merely rode are measured but never backing, and how B/A shows how much of a token's inclusive claim is its own.

A token can be in a transaction in two ways. The transaction can have been bought for it, or the token can merely ride a transaction that would have happened anyway. BTI keeps the two apart. Bytes a token rode are carriage: measured in full, and never backing. The site documentation puts it this way: carriage answers what moved through the blockspace; backing answers what the blockspace was bought for.

Bought and riding #

A transaction is bought for a token when it exists for that token's operation. Its inputs and outputs, including the funding input, serve the operation and nothing else. Such a claim is dedicated. The ruleset's working test (B1a) is that "every substantive output serves the token or is change"; sale consideration counts as serving the token.

A token rides when the transaction would have happened without it, such as a payment or a consolidation that carried the token along. The ruleset's examples:

a rune drifting through someone's payment;
an inscribed sat being sent;
airdropped dust, which "buys dust-sized backing", and the ruleset says this closes the airdrop attack.

A passive movement like these is a sighting. The location change is recorded as a fact, the byte-diff is zero, and the judgment is carriage.

What each books #

The division formula in ruleset v1 (§6) treats the two cases differently:

pool  = tx.size + Σ enabler shares
dedicated:  A_i = B_i + (pool − ΣB) / n_ded
riding:     A_i = B_i

A dedicated claimant gets its own measured regions (Book B) plus an equal share, among the dedicated claimants, of what is left of the pool. That remainder is the overhead in Book A.
A riding claimant keeps only its own measured regions, so its Book A equals its Book B.
If every claimant aboard is riding, the remainder stays with the transaction. In the ruleset's words, "backing belongs to buyers, and every claimant aboard was a passenger." Case 21 in the case studies, an Omni send that also paid a stranger, is this all-riding case.
By default (mode B25), a claim with no dedication at all is judged carriage and is zero in all three books. A flag, --with-riding-tokens, can promote such claims, and the mode is stamped in the books' metadata.

The free-ride index #

The free-ride index is Book B divided by Book A: the fraction of a token's inclusive claim that is its own measured structure. The ruleset's display law (B9) says Book A is always published with B/A beside it, and names the published indices as the dedicated share and the within-dedicated ratio.

A value near 1 means a protocol built its own transactions. A low value means most of what it claims under the inclusive book is somebody else's payment. The measurements document says two protocols can have identical inclusive totals and mean completely different things, and calls this ratio "the strongest argument that one number was never enough."

Measured cases #

From the July 2026 measurement run (block.space's measurements document):

Open Assets, B/A = 0.72. In the document's words, 29 % of its inclusive claim is riding on payments that were happening anyway.
CoinSpark, a three-regime collapse: 1.00 → 0.91 → 0.09. Measured separately, its regimes read: genesis 0.913, dedicated transfer 0.963 and protocol-unaware carriage 0.405, with a per-claim floor of 0.026. In its late regime CoinSpark moved token state using the default route, with no carrier bytes at all. The document calls it the most extreme free-ride measurement recorded.
EPOBC, free-carrier fraction 1.0. Its colour is encoded entirely in the input-0 nSequence field, which every transaction already has. The marginal bytes for carrying the token are zero. Under Book B it claims essentially nothing; under Book A it claims whole transactions.

The document notes that ratios such as B/A are the durable findings: they hold as measurement advances, while shares of chain totals move.

Where carriage sits in the block #

Carriage is one of the four categories every block divides into, beside claimed, burned and unclaimed bytes. No byte is in two of them, and the four sum to the block's exact size. See conservation.