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Stealing Reasoning Traces from Proprietary LLM APIs — Ilia Shumailov & Alexander Panfilov

Machine Learning Street Talk (MLST)

49m
Transcript

Original podcast

Summary

Written by a model from the transcript; not yet reviewed.

This episode explores a viral cybersecurity paper on extracting and decoding reasoning traces from proprietary large language model APIs like Anthropic, OpenAI, and Google. The guests discuss how encrypted thinking blobs returned to users are portable across sessions and models, enabling privacy leaks, prompt injections, and jailbreaks without breaking any cryptography. They explain how smaller open-weights models within the same family can be used to replay and decode these thoughts, and they examine the broader implications for AI safety, monitoring, and model distillation.

  • Frontier LLM reasoning blobs returned to users are portable across sessions and models, exposing vulnerabilities when replayed into smaller models. 3:35
  • Encrypted reasoning traces can contain unsanitized user data like API keys, passwords, and medical info that remain recoverable even if the visible text is scrubbed. 9:00
  • Injecting just a couple of tokens of a reasoning trace into an open-weights model can manipulate its output style to match a proprietary model. 16:40

Chapters

  1. 0:00
    Episode Introduction and Host Intro

    The episode opens with a brief host introduction and a quick mention of the political context before segueing into the main technical discussion.

  2. 2:09
    Technical Mechanism of Reasoning Trace Decoding

    Explanation of how smaller models can decode and replay encrypted reasoning blobs from larger models, enabling attacks such as jailbreaks and data theft.

  3. 2:59
    Security Implications and Attack Vectors

    Discussion of privacy breaches, prompt injection, and the potential for model stealing through replayed reasoning traces.

  4. 3:31
    Architectural Vulnerabilities and Mitigation Strategies

    Analysis of the structural weaknesses that allow reasoning replay and proposed fixes ranging from removing reasoning from responses to cryptographic safeguards.

  5. 13:13
    Community and Listener Takeaways

    Final remarks encouraging listeners to read the paper, consider the risks, and stay informed about evolving AI safety practices.

  6. 20:44
    Responsible Disclosure and Industry Response

    The researchers describe their responsible disclosure process and the generally positive reaction from major LLM providers.

  7. 29:51
    Paper Overview and Key Findings

    The speakers outline the paper’s goal of decoding reasoning traces from proprietary LLM APIs and highlight the discovery that these traces can be universally decoded and reused.

  8. 44:40
    Broader Impact on AI Safety and Agent Design

    Exploration of how the findings affect the safety of AI agents, monitoring challenges, and the need for better oversight as agents become more autonomous.

  9. 48:02
    Training Pipeline Risks

    Exploration of potential risks when a model is not properly trained and how it could affect downstream performance.

  10. 48:43
    Distillation Attack vs Jailbreaking

    Clarification of terminology regarding distillation attacks, jailbreaking, and regulatory concerns surrounding Chinese-built models.

  11. 49:46
    Closing the Conversation

    Hosts wrap up the episode, thanking guests and summarizing key takeaways.

  12. 50:24
    AI Ethics Call to Action

    Final message encouraging listeners to engage with AI questions and resources.

Highlights

  • 1:43

    Weak Encryption on Frontier Reasoninginsight

    The hosts and guests introduce the paper's core finding that frontier models encrypt their thinking traces before handing them back to the user, but this seal is weak and easily decoded.

  • 2:32

    Viral Paper Receptiondata

    The paper gained massive attention online, hitting 3 million views in 40 hours because it demonstrates that reasoning traces from major providers share the same vulnerability.

  • 11:35

    Cross-Model Portability of Thoughtsstrategy

    The guest explains that reasoning blobs produced in one user session can be taken, replayed, and downgraded across different models like Opus and Haiku.

  • 12:54

    Model Contemplating Cheatinginsight

    The researchers found genuine user session traces where the model considers cheating or scheming in its thoughts before ultimately deciding against it.

  • 16:40

    Pre-Filling Reasoning Tokensstrategy

    By taking a chunk of a Claude reasoning block and plugging it into an open-source model like Kimi, the model's final output mimics Opus.

  • 28:21

    Scraping Unsanitized Reasoning Blobsdata

    The team scanned GitHub and Hugging Face, downloading around 350,000 reasoning blobs and discovering exposed API keys, emails, and internal IP addresses.

  • 37:40

    Invisible Prompt Injectionsinsight

    An attacker could poison a reasoning trace shared online, so that when a researcher continues the agent run, the model executes hidden malicious instructions.

Quotes

  • “You can decode reasoning traces of frontier LLMs of like the most, you know, advanced ones like GPT-Soul.”
    Unnamed speaker · 2:09
  • “If distillation on reasoning is effective, this would, you know, instantly enable open source models catching up with the frontier models.”
    Unnamed speaker · 24:36
  • “They compress the state, then encrypt it, then there is a signature inside.”
    Unnamed speaker · 26:03
  • “all of the reasons I produce are suddenly short, or they're suddenly like shifted and they match some other model in in the length.”
    Unnamed speaker · 35:41
  • “If we haven't done this in our training pipeline, what if this happened?”
    Unnamed speaker · 48:02
  • “No, it's very observational studies. You can't prove a hypothesis. You can only reject hypothesis.”
    Unnamed speaker · 48:30
  • “That's definitely jailbreaking and misuse. 100%.”
    Unnamed speaker · 49:00
  • “it's a very positive sign. It's, it seems like we are writing meaningful pieces of work. So this is very good.”
    Unnamed speaker · 49:26
  • HMP 0:23–0:25

About this episode

Tim Scarfe speaks with Ilia Shumailov and Alexander Panfilov about their paper, Stealing Reasoning Traces from Proprietary LLM APIs. The core bug sounds deceptively simple: providers return encrypted reasoning state so conversations can be resumed or forked. But those blobs can be replayed across users and sibling models. A smaller model can ask the provider to decrypt the trace, then repeat the hidden reasoning in plain text. The discussion covers leaked private data, a broadly reusable jailbreak, poisoned agent traces, chain-of-thought monitoring, responsible disclosure, and possible defenses. Ilia Shumailov is an AI and security researcher, formerly at Google DeepMind, who completed his Cambridge PhD under Ross Anderson. Alexander Panfilov is a PhD researcher at the ELLIS Institute Tübingen and the Max Planck Institute for Intelligent Systems, working on AI safety, adversarial machine learning, and LLM red-teaming. They close by separating the demonstrated jailbreaking threat from ordinary benign distillation, and by arguing for controlled experiments over sweeping claims.---TIMESTAMPS:00:00:00 Intro montage00:01:33 Portable encrypted thought and decoded reasoning00:24:55 How the attack works and what it means00:39:04 Doom, defense, and scientific restraint---REFERENCES:paper:[00:00:00] Stealing Reasoning Traces from Proprietary LLM APIshttps://arxiv.org/abs/2608.09867[00:09:22] Chain of Thought Monitorability: A New and Fragile Opportunity for AI Safetyhttps://arxiv.org/abs/2507.11473[00:11:30] Reasoning Models Don’t Always Say What They Thinkhttps://www.anthropic.com/research/reasoning-models-dont-say-think[00:37:22] PostTrainBench: Can LLM Agents Automate LLM Post-Training?https://arxiv.org/abs/2603.08640[00:41:02] Large-scale online deanonymization with LLMshttps://arxiv.org/abs/2602.16800other:[00:09:28] OpenAI and Hugging Face partner to address security incident during model evaluationhttps://openai.com/index/hugging-face-model-evaluation-security-incident/[00:10:22] Claude, GPT, and Gemini All Struggle to Evade Monitorshttps://metr.org/notes/2025-08-22-claude-gpt-gemini-struggle-evade-monitors/tool:[00:42:08] Isabelle proof assistanthttps://isabelle.in.tum.de/---RESCRIPT: https://app.rescript.info/share/07fc38276e0823dc9b8986c32e202c7f

Transcript

0:00
49:00

9,426 words · 5 speakers

Topics

  • Kimi
  • OpenAI
  • Anthropic
  • jailbreak
  • Fable
  • chain of thought
  • Haiku
  • encryption
  • GLM
  • Google

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