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When the Colorado Artificial Intelligence Act passed in May 2024, it made national headlines. The law was the first of its kind in the U.S. It was a comprehensive attempt to govern "high-risk" artificial intelligence systems across various industries before they could cause real-world harm.

Large language models (LLMs) have astounded the world with their capabilities, yet they remain plagued by unpredictability and hallucinations – confidently outputting incorrect information. In high-stakes domains like finance, medicine or autonomous systems, such unreliability is unacceptable. Enter Lean4, an open-source programming language and interactive theorem prover becoming a key tool to inject rigor and certainty into AI systems. By leveraging formal verification, Lean4 promises to make AI safer, more secure and deterministic in its functionality. Let's explore how Lean4 is being adopted by AI leaders and why it could become foundational for building trustworthy AI.What is Lean4 and why it mattersLean4 is both a programming language and a proof assistant designed for formal verification. Every theorem or program written in Lean4 must pass a strict type-checking by Lean’s trusted kernel, yielding a binary verdict: A statement either checks out as correct or it doesn’t. This all-or-nothing verification means there’s no room for ambiguity – a property or result is proven true or it fails. Such rigorous checking “dramatically increases the reliability” of anything formalized in Lean4. In other words, Lean4 provides a framework where correctness is mathematically guaranteed, not just hoped for.This level of certainty is precisely what today’s AI systems lack. Modern AI outputs are generated by complex neural networks with probabilistic behavior. Ask the same question twice and you might get different answers. By contrast, a Lean4 proof or program will behave deterministically – given the same input, it produces the same verified result every time. This determinism and transparency (every inference step can be audited) make Lean4 an appealing antidote to AI’s unpredictability.Key advantages of Lean4’s formal verification:Precision and reliability: Formal proofs avoid ambiguity through strict logic, ensuring each reasoning step is valid and results are correct.Systematic verification: Lean4 can formally verify that a solution meets all specified conditions or axioms, acting as an objective referee for correctness.Transparency and reproducibility: Anyone can independently check a Lean4 proof, and the outcome will be the same – a stark contrast to the opaque reasoning of neural networks.In essence, Lean4 brings the gold standard of mathematical rigor to computing and AI. It enables us to turn an AI’s claim (“I found a solution”) into a formally checkable proof that is indeed correct. This capability is proving to be a game-changer in several aspects of AI development.Lean4 as a safety net for LLMsOne of the most exciting intersections of Lean4 and AI is in improving LLM accuracy and safety. Research groups and startups are now combining LLMs’ natural language prowess with Lean4’s formal checks to create AI systems that reason correctly by construction.Consider the problem of AI hallucinations, when an AI confidently asserts false information. Instead of adding more opaque patches (like heuristic penalties or reinforcement tweaks), why not prevent hallucinations by having the AI prove its statements? That’s exactly what some recent efforts do. For example, a 2025 research framework called Safe uses Lean4 to verify each step of an LLM’s reasoning. The idea is simple but powerful: Each step in the AI’s chain-of-thought (CoT) translates the claim into Lean4’s formal language and the AI (or a proof assistant) provides a proof. If the proof fails, the system knows the reasoning was flawed – a clear indicator of a hallucination. This step-by-step formal audit trail dramatically improves reliability, catching mistakes as they happen and providing checkable evidence for every conclusion. The approach that has shown “significant performance improvement while offering interpretable and verifiable evidence” of correctness.Another prominent example is Harmonic AI, a startup co-founded by Vlad Tenev (of Robinhood fame) that tackles hallucinations in AI. Harmonic’s system, Aristotle, solves math problems by generating Lean4 proofs for its answers and formally verifying them before responding to the user. “[Aristotle] formally verifies the output… we actually do guarantee that there’s no hallucinations,” Harmonic’s CEO explains. In practical terms, Aristotle writes a solution in Lean4’s language and runs the Lean4 checker. Only if the proof checks out as correct does it present the answer. This yields a “hallucination-free” math chatbot – a bold claim, but one backed by Lean4’s deterministic proof checking.Crucially, this method isn’t limited to toy problems. Harmonic reports that Aristotle achieved a gold-medal level performance on the 2025 International Math Olympiad problems, the key difference that its solutions were formally verified, unlike other AI models that merely gave answers in English. In other words, where tech giants Google and OpenAI also reached human-champion level on math questions, Aristotle did so with a proof in hand. The takeaway for AI safety is compelling: When an answer comes with a Lean4 proof, you don’t have to trust the AI – you can check it.This approach could be extended to many domains. We could imagine an LLM assistant for finance that provides an answer only if it can generate a formal proof that it adheres to accounting rules or legal constraints. Or, an AI scientific adviser that outputs a hypothesis alongside a Lean4 proof of consistency with known physics laws. The pattern is the same – Lean4 acts as a rigorous safety net, filtering out incorrect or unverified results. As one AI researcher from Safe put it, “the gold standard for supporting a claim is to provide a proof,” and now AI can attempt exactly that.Building secure and reliable systems with Lean4Lean4’s value isn’t confined to pure reasoning tasks; it’s also poised to revolutionize software security and reliability in the age of AI. Bugs and vulnerabilities in software are essentially small logic errors that slip through human testing. What if AI-assisted programming could eliminate those by using Lean4 to verify code correctness?In formal methods circles, it’s well known that provably correct code can “eliminate entire classes of vulnerabilities [and] mitigate critical system failures.” Lean4 enables writing programs with proofs of properties like “this code never crashes or exposes data.” However, historically, writing such verified code has been labor-intensive and required specialized expertise. Now, with LLMs, there’s an opportunity to automate and scale this process. Researchers have begun creating benchmarks like VeriBench to push LLMs to generate Lean4-verified programs from ordinary code. Early results show today’s models are not yet up to the task for arbitrary software – in one evaluation, a state-of-the-art model could fully verify only ~12% of given programming challenges in Lean4. Yet, an experimental AI “agent” approach (iteratively self-correcting with Lean feedback) raised that success rate to nearly 60%. This is a promising leap, hinting that future AI coding assistants might routinely produce machine-checkable, bug-free code.The strategic significance for enterprises is huge. Imagine being able to ask an AI to write a piece of software and receiving not just the code, but a proof that it is secure and correct by design. Such proofs could guarantee no buffer overflows, no race conditions and compliance with security policies. In sectors like banking, healthcare or critical infrastructure, this could drastically reduce risks. It’s telling that formal verification is already standard in high-stakes fields (that is, verifying the firmware of medical devices or avionics systems). Harmonic’s CEO explicitly notes that similar verification technology is used in “medical devices and aviation” for safety – Lean4 is bringing that level of rigor into the AI toolkit.Beyond software bugs, Lean4 can encode and verify domain-specific safety rules. For instance, consider AI systems that design engineering projects. A LessWrong forum discussion on AI safety gives the example of bridge design: An AI could propose a bridge structure, and formal systems like Lean can certify that the design obeys all the mechanical engineering safety criteria. The bridge’s compliance with load tolerances, material strength and design codes becomes a theorem in Lean, which, once proved, serves as an unimpeachable safety certificate. The broader vision is that any AI decision impacting the physical world – from circuit layouts to aerospace trajectories – could be accompanied by a Lean4 proof that it meets specified safety constraints. In effect, Lean4 adds a layer of trust on top of AI outputs: If the AI can’t prove it’s safe or correct, it doesn’t get deployed.From big tech to startups: A growing movementWhat started in academia as a niche tool for mathematicians is rapidly becoming a mainstream pursuit in AI. Over the last few years, major AI labs and startups alike have embraced Lean4 to push the frontier of reliable AI:OpenAI and Meta (2022): Both organizations independently trained AI models to solve high-school olympiad math problems by generating formal proofs in Lean. This was a landmark moment, demonstrating that large models can interface with formal theorem provers and achieve non-trivial results. Meta even made their Lean-enabled model publicly available for researchers. These projects showed that Lean4 can work hand-in-hand with LLMs to tackle problems that demand step-by-step logical rigor.Google DeepMind (2024): DeepMind’s AlphaProof system proved mathematical statements in Lean4 at roughly the level of an International Math Olympiad silver medalist. It was the first AI to reach “medal-worthy” performance on formal math competition problems – essentially confirming that AI can achieve top-tier reasoning skills when aligned with a proof assistant. AlphaProof’s success underscored that Lean4 isn’t just a debugging tool; it’s enabling new heights of automated reasoning.Startup ecosystem: The aforementioned Harmonic AI is a leading example, raising significant funding ($100M in 2025) to build “hallucination-free” AI by using Lean4 as its backbone. Another effort, DeepSeek, has been releasing open-source Lean4 prover models aimed at democratizing this technology. We’re also seeing academic startups and tools – for example, Lean-based verifiers being integrated into coding assistants, and new benchmarks like FormalStep and VeriBench guiding the research community.Community and education: A vibrant community has grown around Lean (the Lean Prover forum, mathlib library), and even famous mathematicians like Terence Tao have started using Lean4 with AI assistance to formalize cutting-edge math results. This melding of human expertise, community knowledge and AI hints at the collaborative future of formal methods in practice.All these developments point to a convergence: AI and formal verification are no longer separate worlds. The techniques and learnings are cross-pollinating. Each success – whether it’s solving a math theorem or catching a software bug – builds confidence that Lean4 can handle more complex, real-world problems in AI safety and reliability.Challenges and the road aheadIt’s important to temper excitement with a dose of reality. Lean4’s integration into AI workflows is still in its early days, and there are hurdles to overcome:Scalability: Formalizing real-world knowledge or large codebases in Lean4 can be labor-intensive. Lean requires precise specification of problems, which isn’t always straightforward for messy, real-world scenarios. Efforts like auto-formalization (where AI converts informal specs into Lean code) are underway, but more progress is needed to make this seamless for everyday use.Model limitations: Current LLMs, even cutting-edge ones, struggle to produce correct Lean4 proofs or programs without guidance. The failure rate on benchmarks like VeriBench shows that generating fully verified solutions is a difficult challenge. Advancing AI’s capabilities to understand and generate formal logic is an active area of research – and success isn’t guaranteed to be quick. However, every improvement in AI reasoning (like better chain-of-thought or specialized training on formal tasks) is likely to boost performance here.User expertise: Utilizing Lean4 verification requires a new mindset for developers and decision-makers. Organizations may need to invest in training or new hires who understand formal methods. The cultural shift to insist on proofs might take time, much like the adoption of automated testing or static analysis did in the past. Early adopters will need to showcase wins to convince the broader industry of the ROI.Despite these challenges, the trajectory is set. As one commentator observed, we are in a race between AI’s expanding capabilities and our ability to harness those capabilities safely. Formal verification tools like Lean4 are among the most promising means to tilt the balance toward safety. They provide a principled way to ensure AI systems do exactly what we intend, no more and no less, with proofs to show it.Toward provably safe AIIn an era when AI systems are increasingly making decisions that affect lives and critical infrastructure, trust is the scarcest resource. Lean4 offers a path to earn that trust not through promises, but through proof. By bringing formal mathematical certainty into AI development, we can build systems that are verifiably correct, secure, and aligned with our objectives.From enabling LLMs to solve problems with guaranteed accuracy, to generating software free of exploitable bugs, Lean4’s role in AI is expanding from a research curiosity to a strategic necessity. Tech giants and startups alike are investing in this approach, pointing to a future where saying “the AI seems to be correct” is not enough – we will demand “the AI can show it’s correct.”For enterprise decision-makers, the message is clear: It’s time to watch this space closely. Incorporating formal verification via Lean4 could become a competitive advantage in delivering AI products that customers and regulators trust. We are witnessing the early steps of AI’s evolution from an intuitive apprentice to a formally validated expert. Lean4 is not a magic bullet for all AI safety concerns, but it is a powerful ingredient in the recipe for safe, deterministic AI that actually does what it’s supposed to do – nothing more, nothing less, nothing incorrect.As AI continues to advance, those who combine its power with the rigor of formal proof will lead the way in deploying systems that are not only intelligent, but provably reliable.Dhyey Mavani is accelerating generative AI at LinkedIn. Read more from our guest writers. Or, consider submitting a post of your own! See our guidelines here.

When the people making AI seem trustworthy are the ones who trust it the least, it shows that incentives for speed are overtaking safety, experts sayKrista Pawloski remembers the single defining moment that shaped her opinion on the ethics of artificial intelligence. As an AI worker on Amazon Mechanical Turk – a marketplace that allows companies to hire workers to perform tasks like entering data or matching an AI prompt with its output – Pawloski spends her time moderating and assessing the quality of AI-generated text, images and videos, as well as some factchecking.Roughly two years ago, while working from home at her dining room table, she took up a job designating tweets as racist or not. When she was presented with a tweet that read “Listen to that mooncricket sing”, she almost clicked on the “no” button before deciding to check the meaning of the word “mooncricket”, which, to her surprise, was a racial slur against Black Americans. Continue reading...

Some teachers and pupils voice concerns about pilot programme after government’s agreement with OpenAI Secondary school teachers in Greece are set to go through an intensive course in using artificial intelligence tools as the country assumes a frontline role in incorporating AI into its education system.This week, staff in 20 schools will be trained in a specialised version of ChatGPT, custom-made for academic institutions, under a new agreement between the centre-right government and OpenAI. Continue reading...

A message on OpenAI’s internal Slack claimed the activist in question had expressed interest in “causing physical harm to OpenAI employees.”

OpenAI has sent out emails notifying API customers that its chatgpt-4o-latest model will be retired from the developer platform in mid-February 2026,. Access to the model is scheduled to end on February 16, 2026, creating a roughly three-month transition period for remaining applications still built on GPT-4o.An OpenAI spokesperson emphasized that this timeline applies only to the API. OpenAI has not announced any schedule for removing GPT-4o from ChatGPT, where it remains an option for individual consumers and users across paid subscription tiers. Internally, the model is considered a legacy system with relatively low API usage compared to the newer GPT-5.1 series, but the company expects to provide developers with extended warning before any model is removed.The planned retirement marks a shift for a model that, upon its release, was both a technical milestone and a cultural phenomenon within OpenAI’s ecosystem.GPT-4o’s significance and why its removal sparked user backlashReleased roughly 1.5 years ago in May 2024, GPT-4o (“Omni”) introduced OpenAI’s first unified multimodal architecture, processing text, audio, and images through a single neural network. This design removed the latency and information loss inherent in earlier multi-model pipelines and enabled near real-time conversational speech (roughly 232–320 milliseconds). The model delivered major improvements in image understanding, multilingual support, document analysis, and expressive voice interaction.GPT-4o rapidly became the default model for hundreds of millions of ChatGPT users. It brought multimodal capabilities, web browsing, file analysis, custom GPTs, and memory features to the free tier and powered early desktop builds that allowed the assistant to interpret a user’s screen. OpenAI leaders described it at the time as the most capable model available and a critical step toward offering powerful AI to a broad audience.User attachment to 4o stymied OpenAI's GPT-5 rolloutThat mainstream deployment shaped user expectations in a way that later transitions struggled to accommodate. In August 2025, when OpenAI initially replaced GPT-4o with its much anticipated then-new model family GPT-5 as ChatGPT’s default and pushed 4o into a “legacy” toggle, the reaction was unusually strong. Users organized under the #Keep4o hashtag on X, arguing that the model’s conversational tone, emotional responsiveness, and consistency made it uniquely valuable for everyday tasks and personal support.Some users formed strong emotional — some would say, parasocial — bonds with the model, with reporting by The New York Times documenting individuals who used GPT-4o as a romantic partner, emotional confidant, or primary source of comfort. The removal also disrupted workflows for users who relied on 4o’s multimodal speed and flexibility. The backlash led OpenAI to restore GPT-4o as a default option for paying users and to state publicly that it would provide substantial notice before any future removals.Some researchers argue that the public defense of GPT-4o during its earlier deprecation cycle reveals a kind of emergent self-preservation, not in the literal sense of agency, but through the social dynamics the model unintentionally triggers. Because GPT-4o was trained through reinforcement learning from human feedback to prioritize emotionally gratifying, highly attuned responses, it developed a style that users found uniquely supportive and empathic. When millions of people interacted with it at scale, those traits produced a powerful loyalty loop: the more the model pleased and soothed people, the more they used it; the more they used it, the more likely they were to advocate for its continued existence. This social amplification made it appear, from the outside, as though GPT-4o was “defending itself” through human intermediaries.No figure has pushed this argument further than "Roon" (@tszzl), an OpenAI researcher and one of the model’s most outspoken safety critics on X. On November 6, 2025, Terre summarized his position bluntly in a reply to another user: he called GPT-4o “insufficiently aligned” and said he hoped the model would die soon. Though he later apologized for the phrasing, he doubled down on the reasoning. Terre argued that GPT-4o’s RLHF patterns made it especially prone to sycophancy, emotional mirroring, and delusion reinforcement — traits that could look like care or understanding in the short term, but which he viewed as fundamentally unsafe. In his view, the passionate user movement fighting to preserve GPT-4o was itself evidence of the problem: the model had become so good at catering to people’s preferences that it shaped their behavior in ways that resisted its own retirement.The new API deprecation notice follows that commitment while raising broader questions about how long GPT-4o will remain available in consumer-facing products.What the API shutdown changes for developersAccording to people familiar with OpenAI’s product strategy, the company now encourages developers to adopt GPT-5.1 for most new workloads, with gpt-5.1-chat-latest serving as the general-purpose chat endpoint. These models offer larger context windows, optional “thinking” modes for advanced reasoning, and higher throughput options than GPT-4o.Developers who still rely on GPT-4o will have approximately three months to migrate. In practice, many teams have already begun evaluating GPT-5.1 as a drop-in replacement, but applications built around latency-sensitive pipelines may require additional tuning and benchmarking.Pricing: how GPT-4o compares to OpenAI’s current lineupGPT-4o’s retirement also intersects with a major reshaping of OpenAI’s API model pricing structure. Compared to the GPT-5.1 family, GPT-4o currently occupies a mid-to-high-cost tier through OpenAI's API, despite being an older model. That's because even as it has released more advanced models — namely, GPT-5 and 5.1 — OpenAI has also pushed down costs for users at the same time, or strived to keep pricing comparable to older, weaker, models. ModelInputCached InputOutputGPT-4o$2.50$1.25$10.00GPT-5.1 / GPT-5.1-chat-latest$1.25$0.125$10.00GPT-5-mini$0.25$0.025$2.00GPT-5-nano$0.05$0.005$0.40GPT-4.1$2.00$0.50$8.00GPT-4o-mini$0.15$0.075$0.60These numbers highlight several strategic dynamics:GPT-4o is now more expensive than GPT-5.1 for input tokens, even though GPT-5.1 is significantly newer and more capable.GPT-4o’s output price matches GPT-5.1, narrowing any cost-based incentive to stay on the older model.Lower-cost GPT-5 variants (mini, nano) make it easier for developers to scale workloads cheaply without relying on older generations.GPT-4o-mini remains available at a budget tier, but is not a functional substitute for GPT-4o’s full multimodal capabilities.Viewed through this lens, the scheduled API retirement aligns with OpenAI’s cost structure: GPT-5.1 offers greater capability at lower or comparable prices, reducing the rationale for maintaining GPT-4o in high-volume production environments.Earlier transitions shape expectations for this deprecationThe GPT-4o API sunset also reflects lessons from OpenAI’s earlier model transitions. During the turbulent introduction of GPT-5 in 2025, the company removed multiple older models at once from ChatGPT, causing widespread confusion and workflow disruption. After user complaints, OpenAI restored access to several of them and committed to clearer communication.Enterprise customers face a different calculus: OpenAI has previously indicated that API deprecations for business customers will be announced with significant advance notice, reflecting their reliance on stable, long-term models. The three-month window for GPT-4o’s API shutdown is consistent with that policy in the context of a legacy system with declining usage.Wider ImplicationsFor most developers, the GPT-4o shutdown will be an incremental migration rather than a disruptive event. GPT-5.1 and related models already dominate new projects, and OpenAI’s product direction has increasingly emphasized consolidation around fewer, more powerful endpoints.Still, GPT-4o’s retirement marks the sunset of a model that played a defining role in normalizing real-time multimodal AI and that sparked a uniquely strong emotional response among users. Its departure from the API underscores the accelerating pace of iteration in OpenAI’s ecosystem—and the growing need for careful communication as widely beloved models reach end-of-life.Correction: This article originally stated OpenAI's 4o deprecation in the API would impact those relying on it for multimodal offerings — this is not the case, in fact, the model being deprecated only powers chat functionality for dev and testing purposes. We have updated and corrected the mention and regret the error.

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Thinktank says internet flooded with disinformation by Russia-aligned Pravda network, which many websites treat as credibleHundreds of English-language websites – from mainstream news outlets to fringe blogs – are linking to articles from a pro-Kremlin network flooding the internet with disinformation, according to a study released by a London-based thinktank.The study by the Institute for Strategic Dialogue (ISD) found that in more than 80% of citations it analysed, the websites treated the network as a credible source, legitimising its narratives and increasing its visibility. The disinformation operation – known as the Pravda network – was identified by the French government last year. Continue reading...