TransNexus's May STIR/SHAKEN numbers: watch coverage, not participation

TransNexus has posted its May STIR/SHAKEN statistics, the latest in a monthly series it has run since April 2021, drawn from signed calls received by hundreds of voice service providers using its tools. It’s a small, consistent dataset — useful precisely because the cadence lets you watch a trend rather than a snapshot.

The through-line worth tracking is the divergence between participation and coverage. The count of SHAKEN-authorized providers keeps climbing, yet the share of calls actually arriving signed at termination has been stuck — 42.3% in April, down again from the month before. TransNexus’s own explanation is the structural one: calls routed over non-IP segments lose their SHAKEN authentication in transit, so adding signers at the edges does little when the middle of the path still strips signatures. More participants, flat coverage, for a reason that won’t fix itself without the legacy-TDM problem being addressed.

The second thing to keep an eye on is the attestation mix among prolific robocall signers, which in recent months has shifted toward heavy A-level signing — the over-attestation pattern TNS flagged in its annual report, where a valid signature proves the signer signed, not that the call deserved an A. Whether May continues that shift is the number to read off this drop.

It’s a series worth reading against YouMail’s volume index and the KYUP docket: coverage that stays pinned in the low 40s is the empirical case that authentication alone isn’t closing the gap, and that the fix has to reach the upstream and the legacy-transport layers the signatures never survive.