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

GPT-5.6 Rumors Heat Up as Users Swear ChatGPT Suddenly Got Smarter

A formal release for GPT-5.6 is rumored for next week, but OpenAI has yet to announce plans. Something felt different in ChatGPT this week -- and a lot of people noticed at once. Across X, testers spent the past two days swapping screenshots and stopwatch times, all pointing to one theory: OpenAI is quietly A/B testing GPT-5.6 inside ChatGPT, swapped in for some users who select GPT-5.5 Pro. Developer Anshu Chimala posted a side-by-side video on Thursday comparing one-shot landing pages, captioning it: "Well well well, I'm one of the lucky ones with early GPT-5.6 Pro access." Developer Dobroslav Radosavljevič posted on X that whatever he's running inside Codex, OpenAI's coding agent, "feels waaaaaaaay different than [the] 5.5 model." Replies underneath split between believers and people calling it placebo. The clearest pattern across the posts is time. Conor Dart, one of the many X users amplifying the rumors, ran the test with a one-prompt 3D browser game -- with physics and camera controls -- that took just over an hour to generate, versus GPT-5.5 Pro's usual 10-minute mark. "Not perfect, but for a one-prompt AI game dev test, this is seriously impressive," Dart wrote. AI insider Chetas Lua reported a similar slowdown testing a robotic simulation, also pretty sure his results come from OpenAI's new model: "GPT 5.6 Pro continues to mog [Anthropic's Fable 5] in 3D test," he wrote. "Working on games one shot too." In a separate post, he noted response times stretching to 20 or 40 minutes, a pace he said hadn't shown up since before GPT-5.5 shipped. Not every comparison flattered the rumored model. Chris, an AI benchmarker on X, gave two models the same 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. "As I've said before, based on great authority, GPT-5.6 will be an incremental/solid improvement over GPT-5.5, not a Fable killer," he wrote, while noting Fable 5 still beat both models on the spaceship's core geometry. "My rough expectation has been that it would trade blows with Fable 5 on some benchmarks, maybe win around half depending on the category, but not clearly surpass it overall." A separate post attributed to leaker Pankaj Kumar detailed leaks going further: a knowledge cutoff pushed to December 2025, a reasoning-effort setting some testers call "Juice Value" allegedly raised to 960 from 768, and SVG and 3D design generation strong enough to beat Fable 5 on some tasks. None of it comes from OpenAI -- but the details are consistent across accounts: stronger reasoning, an unfinished front end, and a release candidate nicknamed Kindle-Alpha. An AI influencer known as Leo, citing unnamed sources, wrote in a thread that the suspected model is "now being stealth tested when 5.5 Pro is selected in ChatGPT," at least for some Pro accounts, with a planned public launch the following Thursday, June 25. The closest thing to an OpenAI fingerprint on any of this is a memo, not a tweet. Chief scientist Jakub Pachocki reportedly told staff the next model is a meaningful improvement over GPT-5.5, according to a report from The Information. That's still not confirmation of A/B testing, a release date, or any spec floating around X, but it does confirm a new model has been brewing. Decrypt reached out to OpenAI to ask whether GPT-5.6 is being tested inside ChatGPT, but the company did not respond by the time of publication. Why OpenAI might be in a hurry If OpenAI is rushing a new flagship model out the door, it has reasons to. China's open-source model GLM-5.2 trails Claude Opus 4.8 by just one point on FrontierSWE -- a benchmark that scores AI agents on multi-hour, open-ended engineering projects by dominance rate -- while beating GPT-5.5 outright on the same test. Anthropic, meanwhile, is dealing with damage of its own making. The company's flagship Mythos 5 and Fable 5 models remain pulled under a U.S. export control directive issued June 12 over a disputed jailbreak vulnerability, leaving a gap at the top of the market that GLM-5.2 and a hypothetical GPT-5.6 are both positioned to fill. If Anthropic CEO Dario Amodei and President Donald Trump make peace, then Fable 5 would be much more powerful than any other model currently available, with the quality gap between Anthropic's top model and OpenAI's becoming much bigger than before. There's also money on the table. OpenAI is reportedly weighing price cuts on the tokens it charges developers and enterprises, according to the Wall Street Journal, in anticipation of Anthropic doing the same as both companies prepare for dueling IPOs. Whether any of it adds up to an actual GPT-5.6 release is something only OpenAI can confirm, and the company has stayed quiet through a week of leaked checkpoints and stealth-testing claims. Polymarket traders aren't waiting around, however -- contracts on a launch between June 22 and June 28 have priced as high as 89% this week.

OpenAI's Stealth Tests Reveal ChatGPT 5.6 Pro's True Power

OpenAI's upcoming GPT-5.6 Pro has sparked widespread discussion within the AI community, with many eager to see how it measures up against established competitors like Fable 5. According to Universe of AI, this new model promises significant advancements in reasoning and logic, alongside creative problem-solving capabilities. Notably, GPT-5.6 Pro has demonstrated proficiency in generating intricate 3D designs, such as detailed BMW prototypes, showcasing its ability to merge technical precision with creative output. However, its longer processing times for complex tasks, ranging from 20 to 40 minutes, highlight a potential limitation, especially when compared to the faster response rates of Fable 5. Explore how GPT-5.6 Pro's enhanced backend coding capabilities, including strengths in 3.js and SVG generation, could appeal to developers working on dynamic projects. Gain insight into its iterative development process, which has included stealth testing under the GPT-5.5 Pro label to refine its performance. Additionally, understand the challenges it faces in front-end web development and how these limitations might impact its broader adoption. This explainer offers a balanced look at what GPT-5.6 Pro brings to the table and where it still has room to grow. What to Expect from the ChatGPT 5.6 Pro Release The AI community is eagerly awaiting the debut of GPT-5.6 Pro. Reports indicate that OpenAI has been conducting stealth testing under the guise of GPT-5.5 Pro, using this phase to refine the model's features and address potential issues. This approach reflects OpenAI's iterative development strategy, which prioritizes gradual, measurable improvements over sweeping changes. If the rumored release date holds true, GPT-5.6 Pro could represent a pivotal step forward in AI technology, offering new capabilities that cater to both technical and creative applications. The model is expected to excel in areas such as advanced reasoning, creative design and backend development, making it a versatile tool for a wide range of industries. However, questions remain about whether these enhancements will be enough to outpace competitors like Fable 5, which has already established itself as a leader in efficiency and reliability. Key Performance Upgrades GPT-5.6 Pro introduces a host of upgrades designed to enhance its performance across multiple domains. One of its standout features is its improved reasoning and logic capabilities, which enable it to tackle complex tasks with greater accuracy and consistency. For example, the model has demonstrated proficiency in generating intricate 3D designs, such as detailed BMW prototypes and snowy cityscapes. These outputs highlight its ability to combine technical precision with creative innovation, making it a valuable tool for industries that require both. In addition to creative tasks, GPT-5.6 Pro shows significant advancements in backend coding. It performs particularly well in areas like 3.js, SVG generation and simulation modeling, offering developers a powerful resource for creating dynamic and interactive projects. These improvements underscore OpenAI's commitment to balancing technical rigor with creative versatility, making sure the model remains relevant across diverse use cases. Gain further expertise in ChatGPT 5 by checking out these recommendations. How Does GPT-5.6 Pro Compare to Fable 5? When compared to Fable 5, GPT-5.6 Pro demonstrates strengths in several key areas. Its enhanced reasoning and logic capabilities often rival or surpass those of its competitor, particularly when solving complex problems. The model's ability to handle backend development and 3D modeling further highlights its adaptability, positioning it as a strong contender in the AI landscape. However, Fable 5 retains certain advantages. For instance, while GPT-5.6 Pro delivers high-quality outputs, its processing times for complex tasks, ranging from 20 to 40 minutes, can be a significant drawback in time-sensitive scenarios. In contrast, Fable 5 offers faster response rates, making it a more practical choice for users who prioritize efficiency. Additionally, Fable 5 exhibits greater consistency in maintaining logical coherence and avoiding unnecessary elements, which enhances its reliability in critical applications. Limitations to Address Despite its impressive capabilities, GPT-5.6 Pro is not without its limitations. One notable challenge lies in front-end web development, where the model occasionally struggles to produce optimized and user-friendly designs. This shortcoming can require manual intervention to refine outputs, reducing its overall efficiency in this domain. Another area of concern is processing efficiency. The model's longer processing times can hinder its usability, particularly for users who need quick solutions. This limitation stands in stark contrast to Fable 5, which offers faster and more consistent performance. Additionally, while GPT-5.6 Pro has made strides in reasoning, some outputs still include redundant or irrelevant elements, indicating room for further optimization. Stealth Testing and Future Applications Evidence suggests that OpenAI has been conducting stealth testing of GPT-5.6 Pro under the GPT-5.5 Pro label within ChatGPT. This strategy allows the company to gather real-world user feedback, allowing them to fine-tune the model before its official release. By using this approach, OpenAI aims to ensure that GPT-5.6 Pro meets the needs of its diverse user base, from developers to creative professionals. Looking ahead, OpenAI appears to be focusing on enhancing the model's reasoning capabilities for potential integration into Codex workflows. This move could significantly expand GPT-5.6 Pro's utility for technical users, particularly those working in software development and other specialized fields. If successful, these efforts could position GPT-5.6 Pro as a leading tool for both technical innovation and creative exploration. Potential Impact and Future Prospects GPT-5.6 Pro represents a significant milestone in AI development, offering notable advancements in reasoning, creative tasks and backend coding. Its ability to generate intricate designs and handle complex coding challenges makes it a versatile tool for a wide range of applications. However, areas like front-end web development and processing efficiency remain hurdles that OpenAI must address to fully unlock the model's potential. As OpenAI continues to refine its technology, GPT-5.6 Pro has the potential to become a cornerstone in the AI landscape. By addressing its current limitations and building on its strengths, the model could set a new standard for what AI can achieve in both technical and creative domains. The coming months will reveal whether GPT-5.6 Pro can live up to its promise and establish itself as a true leader in the field. Media Credit: Universe of AI Disclosure: Some of our articles include affiliate links. If you buy something through one of these links, Geeky Gadgets may earn an affiliate commission. Learn about our Disclosure Policy.