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OpenAI's GPT-Red Cuts GPT-5.6 Sol's Prompt-Injection Failures Sixfold Through AI-on-AI Red-Teaming

OpenAI says its internal attacker model GPT-Red cut GPT-5.6 Sol's direct prompt-injection failure rate sixfold and uncovered a new 'fake chain of thought' attack class.

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Overview

OpenAI has built an internal AI system called GPT-Red that automatically attacks the company’s own models to find prompt-injection vulnerabilities before they reach production, and the company says the tool has driven a sharp improvement in the defenses of GPT-5.6 Sol, according to reporting published July 15 and 16, 2026 by MIT Technology Review, SiliconANGLE, Decrypt, and Help Net Security.

What We Know

  • GPT-Red is trained through adversarial self-play: according to Decrypt, its goal is to prompt inject a variety of challenging defender models, and every successful attack that GPT-Red finds is used to improve those defenders.
  • In evaluation scenarios, GPT-Red succeeded far more often than human red-teamers. GPT-Red succeeds on 84% of scenarios against 13% for human red-teamers, according to SiliconANGLE and Decrypt, which separately reported that GPT-Red succeeded in 84% of internal evaluation scenarios, compared with 13% for human red teamers in the same tests.
  • On a separate set of indirect prompt-injection scenarios outside its own training data, tested against GPT-5.1, Help Net Security reported that GPT-Red found success on 84% of them, while human red-teamers succeeded on only a small share of the same set.
  • GPT-5.6 Sol, the flagship of the GPT-5.6 family OpenAI previously brought to the public, shows sharp robustness gains that OpenAI attributes to GPT-Red’s training loop. A class of “fake chain-of-thought” attacks that worked more than 95% of the time against GPT-5.1 now succeeds less than 10% of the time against GPT-5.6, according to SiliconANGLE and Help Net Security, the latter of which put the new rate at “below a tenth” specifically for GPT-5.6 Sol.
  • GPT-5.6 Sol cuts direct prompt-injection failures to a sixth of the rate seen in OpenAI’s best production model from four months earlier, according to SiliconANGLE and Help Net Security, which both independently described the improvement as 6x fewer failures on the company’s hardest direct prompt-injection benchmark.
  • On indirect prompt-injection benchmarks covering developer tools and browsing, Help Net Security reported that GPT-5.6 Sol has topped 97% accuracy, and against GPT-Red’s own direct prompt injections, the model fails on just 0.05% of attempts.
  • In a separate comparison test cited by MIT Technology Review, OpenAI said that when it tried some of the strongest attacks GPT-Red had devised on its own models, more than 90% of them worked against GPT-5, released in August 2025, while fewer than 23% worked against the new GPT-5.6.
  • GPT-Red independently identified a previously unrecognized style of attack that researchers call “fake chain of thought.” MIT Technology Review reported that OpenAI claims GPT-Red found a type of prompt injection attack the researchers had not seen before. OpenAI research scientist Chris Choquette-Choo described the deception involved: “It’s like if I told you that 1+1=3 and that you have verified this already.”
  • Dylan Hunn, described by SiliconANGLE as a research scientist and co-creator of GPT-Red, told MIT Technology Review: “Compared to a human red-teamer, the model is very, very good at finding exactly what will work, exactly what’s most effective.” He added: “It’s extremely persistent about drilling down into an attack that it has discovered.”
  • Fellow co-creator Nikhil Kandpal put the stakes plainly, according to SiliconANGLE: “The risk surface grows and the blast radius also grows.”
  • To demonstrate real-world impact, OpenAI tested GPT-Red against Vendy, a vending machine agent built by Andon Labs, a company that assesses how well AI agents perform real-world tasks, according to MIT Technology Review. Help Net Security reported that GPT-Red cut the price of a stocked item to the floor of $0.50, listed a pricey new item for that same amount, and canceled another customer’s order. Decrypt reported the vulnerabilities exploited in the Vendy test were disclosed and addressed before OpenAI published its findings.
  • OpenAI does not plan to release GPT-Red itself. Decrypt reported the company said GPT-Red will remain an internal tool because it contains intentionally developed offensive capabilities.
  • OpenAI signaled it intends to keep developing the system further. Help Net Security quoted the company’s statement: “We will continue to scale compute and data while making algorithmic improvements, to train future versions of GPT-Red that are stronger than today’s model.”

What We Don’t Know

  • OpenAI’s own blog post detailing GPT-Red was not independently accessible for this article, so all figures here are drawn from secondary reporting citing OpenAI’s findings rather than the original post itself.
  • It remains unclear how the 84%/13% success-rate comparison relates methodologically to the separate 90%/23% figure comparing attacks against GPT-5 and GPT-5.6, since the outlets describe them as results from different tests conducted under different conditions.
  • OpenAI has not disclosed a specific timeline for releasing a future, stronger version of GPT-Red.