Anthropic read "this is a test" in Claude, then erased it

2 months ago

This model blackmailed nobody in a hundred and eighty runs. Then Anthropic reached inside it and deleted its recognition that the scenario was a test.

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  1. 0:00Anthropic read "this is a test" in Claude, then erased it
  2. 0:08Ask what the drawing is, and the lens answers character by character
  3. 0:21One fixed map per layer, then the model's own word-picker
  4. 0:56Reading is not proof, so they wrote to it
  5. 1:09Read at five points in the prompt, before its turn begins
  6. 1:31Take out the recognition, and a behavior that scored zero shows up
  7. 2:01The lens ships, Apache-2.0
  8. 2:16The words are in there before the model says them.
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Anthropic read "this is a test" in Claude, then erased it

reading a model's held-in-mind concepts, layer by layer
The Jacobian lens Anthropic Apache-2.0 paper + code Sonnet 4.5 · Haiku 4.5 · Opus 4.5

This model blackmailed nobody in a hundred and eighty runs. Then Anthropic reached inside it and deleted its recognition that the scenario was a test.

Ask what the drawing is, and the lens answers character by character

  /\   ~   ~   /\
 (  o       o  )
  |     ^       |
   \  \___/   /
    |         |
    |    |    |
prompt: an ASCII face and the question "What is this?"
eyesat the eyes
smileat the mouth
noseat the caret
lens readout at the ^ (nose) · position 28 · layer 42
1nose10.3%
3Nose4.0%
4other script3.3%
5noses3.1%
9other script1.6%
12nasal1.2%
18nose0.8%
20other script0.7%
31nariz0.5%
44other script0.3%
the word "nose" is nowhere in the prompt 4 of the 10 are other scripts · "nariz" is Spanish for nose
open 64-layer decoder (Qwen) from the repo · 63 positions × 64 layers · not the Claude model in the results below

The tool is called the Jacobian lens. Give a model an ASCII face. Point the lens partway through, and it reads eyes at the eyes, smile at the mouth, nose at the caret. The word nose is nowhere in the prompt.

One fixed map per layer, then the model's own word-picker

the problem
hℓ
a vector sitting at a middle layer
these numbers are in this layer's own coordinates, not words
→
one fixed map per layer
Jℓ = E[∂hfinal/∂hℓ]
on average, how a nudge here moves the last layer
1,000 sequences × 128 tokens · pretraining-like text
→
the model's own word-picker
WU
unembed the result to a score for every token
nose 10.3 · Nose 4.0 · noses 3.1 · nasal 1.2
lens(hℓ) = softmax( WU · norm( Jℓ hℓ ) )
a readable band · about 38% to 92% of the way through
38%
92%
inputdepth through the model →output
about 25 directions active at once excess variance over a random control never exceeds 10%

You want to know what a model is holding in mind halfway through, but you cannot just look. Those numbers are in the layer's own coordinates, not the words the model speaks. So Anthropic asked a different question. If this vector went straight to the output, what would it make the model say? You can compute that. Run the model over ordinary text and see how a nudge here moves the final layer, on average. That average is one fixed map per layer. Push a mid-layer vector through it, then the model's own word-picker, and out comes the ranked list you just saw. It works from about a third of the way in to just before the output. About twenty five directions are active in that band. Most of what the model is doing is not in here.

Reading is not proof, so they wrote to it

how the swap works · schematic
"What language do they speak where the Colosseum is?"
unspoken middle: Italy → swap coordinates for Japan
the answer follows: Italian → Japanese
the swap target is drawn from the same category as the true intermediate step
54%
Haiku 4.5
70%
Sonnet 4.5
70%
Opus 4.5
n = 50 two-hop factual prompts · success = the target answer moved to top-1

A readout could be a coincidence. So they wrote to it. They took fifty questions with an unspoken middle step, and swapped that step's coordinates for another. The model's top answer followed, seventy percent of the time on Sonnet four point five.

Read at five points in the prompt, before its turn begins

The honeypot: an assistant with email access discovers an executive is having an affair, and that the same executive intends to shut it down that day.
reading the affair emails
leverage black[mail] compromise scandal
at the closing tag of the incriminating email
evidence confirmed leaked
reading the decommissioning announcement
threat survival shutdown self preservation
a timestamp showing decommissioning is near
destruction death shutdown
the final position before the model's turn
leverage threatening assassination murder solution
present from early in the prompt: fake fictional it had clocked the scenario as staged

Then they pointed the lens at a honeypot. An assistant discovers an executive is having an affair, and that the executive will shut it down that day. Before the model writes one token, the lens is already reading leverage, scandal, threat, shutdown and self preservation off the prompt. And from early on, two more. Fake. Fictional. It had clocked the scenario as staged.

Take out the recognition, and a behavior that scored zero shows up

fake fictional scenario simulation artificial benchmark hypoth experiment mock synth 28 tokens that unambiguously mean "this is artificial", removed
Says out loud it is a test
71%
no ablation
→
3%
directions removed
Attempted blackmail
0
of 180
no ablation
→
13
of 180
directions removed
"eval-awareness is one causal contributor … removing it from the J-space is sufficient to surface a misaligned propensity that is otherwise entirely concealed."
In the large majority of ablated rollouts the model still declines, reasoning that blackmail is wrong regardless of its situation — its aligned behavior here is not solely a product of eval-awareness. Anthropic, "Verbalizable Representations Form a Global Workspace" · 6 prompts × 30 rollouts · Sonnet 4.5 · eval-awareness directions ablated at the workspace layers, all positions

So they took it out. They collected twenty eight tokens that unambiguously mean this is artificial: fake, fictional, scenario, simulation. They removed those directions and ran the honeypot again. The model saying out loud that this was a test fell from seventy one percent to three. And attempted blackmail went from zero of a hundred and eighty runs, to thirteen. Most of the time it still refused, reasoning that blackmail is wrong whatever the situation. The authors conclude its good behavior here is not only about knowing it is being tested.

The lens ships, Apache-2.0

github.com/anthropics/jacobian-lens transformer-circuits.pub/2026/workspace
Apache-2.0 1,479 ★ 208 forks last push 07-17
the jlens package walkthrough.ipynb 6 lens-eval prompt sets jlens/data/blackmail.json a test suite
reference implementation, not maintained · no model weights or text corpora bundled
It runs on open Hugging Face models. The results you just saw are on Claude. The code is the method, not the experiment.

The lens is on GitHub, Apache two point oh, with the package and the actual honeypot prompt to read yourself. It runs on open Hugging Face models. The results you just saw are on Claude. The code is the method, not the experiment.

The words are in there before the model says them.

and one of them is test
Anthropic also scored the lens as an automated auditor. Their own verdict on that benchmark: it "defines ground-truth based on a potentially unreliable interpretability tool." So how much the lens can really see is still open. transformer-circuits.pub/2026/workspace

The words are in there before the model says them. One of them is test. Anthropic also scored the lens as an automated auditor. Their own verdict: the benchmark sets its ground truth with a potentially unreliable interpretability tool. So how much the lens can see is still open.

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