GPT-5.6 stealth tests suggest OpenAI's new AI model brings stronger reasoning but slower speeds

OpenAI Appears to Be Testing GPT-5.6 Behind the Scenes

Something shifted inside ChatGPT this week, and users noticed immediately. Developers and AI testers flooded social media with side-by-side comparisons, stopwatch screenshots, and detailed performance logs, all pointing to the same conclusion: OpenAI is conducting stealth tests of GPT-5.6, quietly swapping it in for select users who choose GPT-5.5 Pro 1

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. The company has not confirmed the tests, but the pattern of reports suggests a new AI model is already in limited circulation.

Developer Anshu Chimala shared a video comparison showing one-shot landing page generation that appeared markedly different from previous outputs. Meanwhile, Dobroslav Radosavljevič reported that whatever he encountered inside Codex "feels waaaaaaaay different" from the GPT-5.5 model 1

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. The clearest signal came from response times: tasks that previously took 10 minutes now stretched to over an hour, with some complex simulations requiring 20 to 40 minutes to complete 1

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Extended Response Times Signal Deeper Reasoning

The longer processing windows appear tied to enhanced reasoning and logic capabilities. Conor Dart tested the suspected model with a one-prompt 3D browser game featuring physics and camera controls, which took just over an hour to generate compared to GPT-5.5 Pro's typical 10-minute mark 1

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. AI insider Chetas Lua reported similar slowdowns while testing robotic simulations, noting that such extended response times hadn't appeared since before GPT-5.5 shipped 1

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Not every comparison favored the new model. AI benchmarker Chris gave both models an identical spaceship-building prompt: the suspected GPT-5.6 Pro worked for 87 minutes against GPT-5.5 Extra High's 34 minutes and 42 seconds 1

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. He characterized the incremental improvements over GPT-5.5 as solid but not dominant, predicting the model would trade blows with Fable 5 on some benchmarks while falling short on others.

Technical Upgrades Point to Creative Problem-Solving Gains

Leaked specifications circulating among testers describe a knowledge cutoff pushed to December 2025 and a reasoning-effort setting dubbed "Juice Value" allegedly raised to 960 from 768 1

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. The model reportedly excels at backend coding, particularly in 3.js and SVG generation, alongside impressive 3D generation capabilities 2

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. Users have shared examples of intricate 3D designs, including detailed BMW prototypes and snowy cityscapes, showcasing the model's ability to merge technical precision with creative output 2

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These advancements suggest OpenAI has prioritized creative problem-solving and complex task handling over speed. The model's proficiency in simulation modeling and dynamic project development makes it particularly relevant for developers working on interactive applications 2

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. However, reports also indicate limitations in front-end web development, where outputs occasionally require manual refinement 2

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Competitive Pressures Drive Accelerated Timeline

If OpenAI is rushing GPT-5.6 to market, the timing reflects mounting competitive pressures. China's open-source GLM-5.2 trails Claude Opus 4.8 by just one point on FrontierSWE—a benchmark measuring AI agents on multi-hour engineering projects—while beating GPT-5.5 outright 1

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. Meanwhile, Anthropic's Fable 5 and Mythos 5 models remain pulled under a U.S. export control directive issued June 12, creating a gap at the top of the market that both GLM-5.2 and a potential GPT-5.6 are positioned to fill 1

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OpenAI Chief Scientist Jakub Pachocki reportedly told staff the next model represents a meaningful improvement over GPT-5.5, according to The Information, though this stops short of confirming A/B testing or a release date 1

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. AI influencer Leo, citing unnamed sources, claimed the model is being stealth-tested for GPT-5.5 Pro users with a planned public launch on Thursday, June 25 1

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. Polymarket traders have priced contracts on a launch between June 22 and June 28 as high as 89% this week 1

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What This Means for Developers and Enterprises

The suspected stealth tests reflect OpenAI's iterative development strategy, which prioritizes measurable improvements through real-world usage before formal announcements 2

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. For developers, the model's backend coding strengths and 3D generation capabilities could open new possibilities in dynamic project development and technical applications. However, the significantly longer processing times—20 to 40 minutes for complex tasks—may limit its appeal in time-sensitive scenarios where Fable 5's faster response times offer a practical advantage 2

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OpenAI is also reportedly weighing price cuts on tokens charged to developers and enterprises, according to the Wall Street Journal, in anticipation of Anthropic doing the same as both companies prepare for dueling IPOs 1

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. This suggests the company is positioning GPT-5.6 not just as a technical upgrade but as part of a broader strategy to maintain market leadership amid intensifying competition. Whether the model delivers enough to justify its longer processing times will depend on how well its stronger reasoning capabilities translate to real-world applications across industries requiring both logic and creative problem-solving.