Summary

  • In ARIN’s Q3 2026 count, just 23 legacy blocks of /15 or larger hold about 38% of the IPv4 space still outside registration services agreements.
  • ARIN handles those blocks as a named list. Its much larger pile of small blocks is most of the casework but a small fraction of the addresses.

The elephants have addresses. In the data-accuracy presentation ARIN posted for its 23 October meeting, 23 legacy blocks of /15 or larger account for about 38% of the IPv4 space still outside registration services agreements. ARIN says it manages that group as a named list. The deck gives no names; it gives the scale of the remaining job.

The wider inventory stands at 16,212 legacy CIDR blocks and 372,877 /24 equivalents in Q3 2026. Another 715 blocks of exactly /16 account for 49.1% of the remaining space. At the other end, blocks from /21 through /24 make up 91.5% of the block count but only 5.9% of the address space. Counting files and counting addresses tell almost opposite stories about where the work sits.

ARIN’s progress has been substantial. The uncontracted address total fell 26,313 /24 equivalents from the preceding quarter and 81% from Q1 2024. In Q4 2025 alone, 2,768 prefixes covering 1.28 million /24 equivalents were brought under registration services agreements, the largest single-quarter change in the programme’s history. That was an agreement milestone, not a mass return of those addresses to the registry.

The remaining giant blocks create a sharp operational choice. ARIN can spend staff time closing many small records or concentrate on the named large-block list where one verified holder and one agreement can move the space measure dramatically. The two measures deserve separate progress reports. A completed small-block contact case is real work, even if it barely moves the address chart.

The slide deck counts blocks, not distinct owners. It gives no block-by-block account of contact verification, successor identification or signed agreements for the 23. The next update can make that list legible in aggregate: how many have a verified holder, how many entered an agreement and how many moved to a different disposition.