Summary

  • ARIN counted 372,877 IPv4 /24 equivalents outside agreements in Q3 2026, 81% below Q1 2024.
  • The remaining stock is lopsided: 23 blocks of /15 or larger account for 38% of the space, while ARIN’s slides place records with unknown holder data on a distinct quarantine-and-release path.

The number looks like a cleanup victory. In Q3 2026, ARIN reported 372,877 IPv4 /24 equivalents not under agreement, down 26,313 in the quarter and 81% since Q1 2024. That is a measure of address-space size, not a count of organizations, records, or prefixes. The same presentation counts 16,212 legacy CIDR blocks, 331 fewer than the previous quarter. Those are different ledgers; adding them together would be accounting by shrug.

The remaining space is concentrated. ARIN says 715 /16 blocks represent 49.1% of it. A separate size band—23 blocks of /15 or larger—accounts for 38%, down from 164 such blocks in Q1 2024. The categories overlap by size definition and should not be added. Nor does the chart say that these blocks are idle, disputed, or held by one organization apiece. It says the residual pool is not evenly distributed.

The quarterly change with the biggest bite came in Q4 2025: 2,768 prefixes totaling 1.28 million /24 equivalents were brought under Registration Services Agreements, primarily large legacy allocations. That helps explain why the aggregate fell sharply. It does not tell us which of the remaining large blocks will follow, or when.

ARIN’s slides also divide its work by the quality of holder data. The presentation lists 2,660 organizations in an “Unknown holder data” cohort, where the organization record has no user contact information, and 10,218 in an outreach pipeline. The latter includes organizations with both contracted and uncontracted resources as well as holders with no existing agreement relationship. These are organization counts, not block counts. A bad contact record is a registry problem; an identified holder who has not signed is a different one.

That distinction matters because ARIN’s slide gives the unknown-data cohort a severe path: stop services or quarantine, a 12-month hold, then release through the waiting list, described as rights extinguishment. The public legacy FAQ, meanwhile, says a holder without an agreement can maintain and update unique registration information and that ARIN has no plan or intention to take away legacy rights solely because no agreement was signed. It also says RPKI and IRR access require an agreement. Those statements concern different conditions. Treating every unsigned holder as an unknown holder would erase the line ARIN itself draws.

The presentation does not give the contact-attempt record, decision authority, appeal route, or exact evidence that moves an organization from outreach to unknown-holder status. Those are the missing rules that would change the assessment of the release path. A shrinking pool is measurable progress; the legitimacy of the last step depends on whether the registry can show its work.

Sources: ARIN 58 Data Accuracy slides; ARIN Day 2 recap; Legacy resources; Legacy FAQ. ARIN 58 Day 2 transcript; Data Accuracy Improvement Program.