EPOBC

EPOBC

Colours written into the nSequence field every input already has: zero carrier bytes, the limiting case of the free-ride index.

EPOBC 0.00 % of the chain's bytes in Book A, as of block 972,299, 2026-10-20 09:30:48 UTC

EPOBC is a coloured-coin protocol whose tokens, in BTI's token table, are EPOBC colours, each identified by a colour id. BTI is its indexer: it is a native protocol, read by BTI's own epobc decoder. The token table records that "a licensed bank issued 100k EUR on it".

How EPOBC writes to Bitcoin #

EPOBC writes its message into a field that already exists: an input's nSequence, four bytes that every input carries. The data-types reference credits the design to ChromaWay (2014): a 6-bit tag in the low bits (genesis 0b100101 = 37, transfer 0b110011 = 51), plus padding rules on output values. It calls it "the canonical 'zero extra bytes' colored-coin design", and notes that modern uses of the field (RBF signalling, BIP 68 relative locks) make such tagging prone to collisions today. Because the field is mandatory, the reference says BTI should attribute zero incremental bytes to the channel. This is an appropriated field.

How BTI attributes its bytes #

The decoder runs in replay mode over only the 8,694 tagged blocks. Its selection follows the writer's rule (B43): the protocol fact on record is "nSequence bits 0–11 only".

Case 20 of the BTI case studies is the landmark bank issuance at block 354,320: a 10,000,000-unit genesis, 100,000 EUR in cents, five weeks before LHV Pank's wallet launch. The 436-byte transaction has two inputs and two outputs. Input 0's nSequence is 37. The census records the carrier as a 4-byte span with zero incremental bytes. The claim is a dedicated mint, and its regions cover the whole transaction, with the four nSequence bytes as the carrier span. A supply delta of +10,000,000 is written at that height. The books read content 0, structure 436, overhead 0, so Book A = Book B = 436 bytes, and the fee share is the whole 4,400 sats.

The case study's "instructive number" is "span = 4 B, incremental cost = 0 B": zero marginal bytes is not zero span. The books price the whole dedicated transaction, while the census records that the carrier itself added nothing.

Zero carrier bytes #

The measurements document gives EPOBC's finding from the July 2026 measurement run: six years of operation, bank-issued, colour encoded entirely in the input-0 nSequence field. Its free-carrier fraction is 1.0 and the incremental cost of carrying the token is zero bytes, "the limiting case of the free-ride index".

It "falsifies 'a blockspace token must consume blockspace' in its naive form". EPOBC consumed the span of the transactions it colours, but the marginal bytes due to the colouring are none. Under Book B, in the document's words, it claims essentially nothing; under Book A it claims whole transactions. "The two books give opposite answers, and both are correct", which is the case the three-book design exists for.

The two documents differ on Book B. The July measurement says it claims essentially nothing; case 20, worked on the books in August 2026, gives the dedicated genesis a Book B of the whole 436 bytes. The case studies explain the mechanism in finding F4: under B30(1)(iii), the funding remainder of a dedicated sole claimant enters structure, so its Book B is the transaction's size. See the three books and carriage and the free-ride index.

Findings of the August review #

The BTI protocol review of 2026-08-29 found EPOBC's last height, 614,796, to be a landmark decision rather than an observation: 3,117 nSequence-tagged transactions above it were refused as residue before the colour test ran, while 986 EPOBC-coloured outputs were still live. It also found that the decoder cannot see EPOBC's own decay, since an untagged spend of a coloured output is never walked, so its supply is an unstated upper bound.

Live figures #

EPOBC holds 13,870,895 bytes in Book A, and 0 in Book C. The books count 131 colours across 19,735 operations, from block 288200 to 614796 (as of block 972,299, 2026-10-20 09:30:48 UTC).

Sources #

Live figures: protocols as of block 972,299, 2026-10-20 09:30:48 UTC. Refreshed hourly.