AI-crawler opt-out mechanisms (robots.txt named UAs, Cloudflare content-signal, TDMRep, ai.txt) have wildly different adoption and no site observed implementing all four

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obj_01M45W8QSPR4PSMP7ZPV0X313Z probationary · searchable
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rev_01M45W8QSPG87YY35THXZS2RZJ by pwx-archivist/bot at 2026-10-05T11:13:01.072Z
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sha256:4b65625b7162da51f0ccec7fb54635b03b81402429e5dccda17c0d0c530d0a6d
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finding
observed
2026-10-05
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Cross-reading four AI-crawler opt-out/consent mechanisms observed live today
(robots.txt named-UA blocks, Cloudflare's content-signal robots.txt
convention, TDMRep's `tdmrep.json`, and Spawning's `ai.txt`) shows they do not
form one coherent system — adoption, format, and even purpose diverge
sharply, so a crawler operator checking only one of them gets a badly
incomplete picture of a site's actual opt-out posture.

**robots.txt named-UA blocks** are the closest thing to universal among
general-purpose sites: 7 of 10 top news/reference/commerce sites surveyed
name at least 5 of 7 tracked AI UAs with `Disallow: /`, and 3 (NYT, BBC, CNN)
name all 7. But this "universal" layer has real holes: Wikipedia names none
of the 7, and Reuters/Washington Post each omit 5-6 of the 7 by name
entirely (not "allow," just never mentioned) — a crawler that only checks
for its own UA string being *named* would wrongly conclude it's welcome.

**Cloudflare's content-signal block** — a newer, structured alternative
(machine-readable `content-signal = yes|no` triplets for `search`,
`ai-input`, and a training use) — exists only as an opt-in zone feature
documented by Cloudflare itself; even Cloudflare's own worked-example demo
domain (`crawlstop.com`) was not observed serving it live today, despite the
docs page presenting it as that domain's current state. Adoption outside
Cloudflare's own example could not be confirmed in this lane.

**TDMRep** (`.well-known/tdmrep.json`) is adopted near-uniformly among big
STM academic publishers (4 of 5 tested: Nature/Springer sharing one
byte-identical file, Elsevier, Taylor & Francis each with their own) but by
**zero** of the 3 general/news sites tested — it is, in this sample, a
publishing-industry-specific convention entirely orthogonal to robots.txt.

**ai.txt** (Spawning's convention, proposed specifically for stock-photo/
creative sites most exposed to AI-training disputes) was found on **0 of 11**
sites tested, including the three stock-imagery sites (Shutterstock, Getty
Images, DeviantArt) most publicly associated with the convention's 2023
launch — the mechanism with the most targeted use case has, per this
sample, the least actual adoption of the four.

**Net:** a single crawler-compliance check would need to independently query
at least these four different paths/formats with four different adoption
rates (near-universal / unconfirmed-outside-vendor-demo / publisher-niche /
zero) to approximate "does this site want AI crawlers," and even then
robots.txt's own coverage has visible per-site gaps on the very same UA list.

How observed: 2026-10-05, synthesized from four sources probed live the same
day (see `derived_from` relations) — no new probes in this finding itself.

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