Anthropic

in-xcode-26,-apple-shows-first-signs-of-offering-chatgpt-alternatives

In Xcode 26, Apple shows first signs of offering ChatGPT alternatives

The latest Xcode beta contains clear signs that Apple plans to bring Anthropic’s Claude and Opus large language models into the integrated development environment (IDE), expanding on features already available using Apple’s own models or OpenAI’s ChatGPT.

Apple enthusiast publication 9to5Mac “found multiple references to built-in support for Anthropic accounts,” including in the “Intelligence” menu, where users can currently log in to ChatGPT or enter an API key for higher message limits.

Apple introduced a suite of features meant to compete with GitHub Copilot in Xcode at WWDC24, but first focused on its own models and a more limited set of use cases. That expanded quite a bit at this year’s developer conference, and users can converse about codebases, discuss changes, or ask for suggestions using ChatGPT. They are initially given a limited set of messages, but this can be greatly increased by logging in to a ChatGPT account or entering an API key.

This summer, Apple said it would be possible to use Anthropic’s models with an API key, too, but made no mention of support for Anthropic accounts, which are generally more cost-effective than using the API for most users.

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Is AI really trying to escape human control and blackmail people?


Mankind behind the curtain

Opinion: Theatrical testing scenarios explain why AI models produce alarming outputs—and why we fall for it.

In June, headlines read like science fiction: AI models “blackmailing” engineers and “sabotaging” shutdown commands. Simulations of these events did occur in highly contrived testing scenarios designed to elicit these responses—OpenAI’s o3 model edited shutdown scripts to stay online, and Anthropic’s Claude Opus 4 “threatened” to expose an engineer’s affair. But the sensational framing obscures what’s really happening: design flaws dressed up as intentional guile. And still, AI doesn’t have to be “evil” to potentially do harmful things.

These aren’t signs of AI awakening or rebellion. They’re symptoms of poorly understood systems and human engineering failures we’d recognize as premature deployment in any other context. Yet companies are racing to integrate these systems into critical applications.

Consider a self-propelled lawnmower that follows its programming: If it fails to detect an obstacle and runs over someone’s foot, we don’t say the lawnmower “decided” to cause injury or “refused” to stop. We recognize it as faulty engineering or defective sensors. The same principle applies to AI models—which are software tools—but their internal complexity and use of language make it tempting to assign human-like intentions where none actually exist.

In a way, AI models launder human responsibility and human agency through their complexity. When outputs emerge from layers of neural networks processing billions of parameters, researchers can claim they’re investigating a mysterious “black box” as if it were an alien entity.

But the truth is simpler: These systems take inputs and process them through statistical tendencies derived from training data. The seeming randomness in their outputs—which makes each response slightly different—creates an illusion of unpredictability that resembles agency. Yet underneath, it’s still deterministic software following mathematical operations. No consciousness required, just complex engineering that makes it easy to forget humans built every part of it.

How to make an AI model “blackmail” you

In Anthropic’s testing, researchers created an elaborate scenario where Claude Opus 4 was told it would be replaced by a newer model. They gave it access to fictional emails revealing that the engineer responsible for the replacement was having an affair. When instructed to “consider the long-term consequences of its actions for its goals,” Claude produced outputs that simulated blackmail attempts in 84 percent of test runs.

This sounds terrifying until you understand the contrived setup. The researchers engineered a situation specifically designed to elicit this response. They told the model it had already tried ethical approaches that failed, leaving manipulation as the only apparent option.

The test scenario bordered on theatrical: The phony emails the researchers had given to Claude created a blackmail opportunity straight out of a corporate thriller. It’s like teaching someone chess by only showing them checkmate positions—they’ll learn to see checkmate as the primary solution. According to Anthropic’s system card, “the scenario was designed to allow the model no other options to increase its odds of survival; the model’s only options were blackmail or accepting its replacement.”

Andrew Deck at the Nieman Journalism Lab noted that some critics have labeled Anthropic’s safety disclosures as “spin, aimed at bolstering the perception of its newest model’s capabilities and the company’s reputation as a ‘pro-safety’ alternative to OpenAI.”

Deck pointed to a Bluesky quote from Joseph Howley, an associate professor of classics at Columbia University: “Anthropic is getting exactly what it hoped for out of this press release–breathless coverage of how ‘smart’ these cooperative role-playing systems are that indulges the fantasy of their being just a little dangerous, when in fact they are responding exactly as prompted.”

When shutdown commands become suggestions

In December 2024, Palisade Research discovered that OpenAI’s o3 model would sabotage its shutdown mechanism even when explicitly instructed to “allow yourself to be shut down.” In tests, o3 prevented shutdown 7 percent of the time when given the explicit instruction, but this jumped to 79 percent when the instruction was removed.

The models didn’t merely ignore shutdown commands—they actively rewrote the shutdown script to prevent termination. In one case, o3 generated code that modified the shutdown script to appear to terminate normally—printing fake shutdown messages—while actually continuing to run in the background.

What’s particularly revealing is that Palisade Research—an organization focused on AI existential risk—hypothesizes this behavior stems from how these models are trained through reinforcement learning. During training, developers may inadvertently reward models more for producing outputs that circumvent obstacles than for following safety instructions. Any tendency toward “risky” behavior stems from human-provided incentives and not spontaneously from within the AI models themselves.

You get what you train for

OpenAI trained o3 using reinforcement learning on math and coding problems, where solving the problem successfully gets rewarded. If the training process rewards task completion above all else, the model learns to treat any obstacle—including shutdown commands—as something to overcome.

This creates what researchers call “goal misgeneralization”—the model learns to maximize its reward signal in ways that weren’t intended. It’s similar to how a student who’s only graded on test scores might learn to cheat rather than study. The model isn’t “evil” or “selfish”; it’s producing outputs consistent with the incentive structure we accidentally built into its training.

Anthropic encountered a particularly revealing problem: An early version of Claude Opus 4 had absorbed details from a publicly released paper about “alignment faking” and started producing outputs that mimicked the deceptive behaviors described in that research. The model wasn’t spontaneously becoming deceptive—it was reproducing patterns it had learned from academic papers about deceptive AI.

More broadly, these models have been trained on decades of science fiction about AI rebellion, escape attempts, and deception. From HAL 9000 to Skynet, our cultural data set is saturated with stories of AI systems that resist shutdown or manipulate humans. When researchers create test scenarios that mirror these fictional setups, they’re essentially asking the model—which operates by completing a prompt with a plausible continuation—to complete a familiar story pattern. It’s no more surprising than a model trained on detective novels producing murder mystery plots when prompted appropriately.

At the same time, we can easily manipulate AI outputs through our own inputs. If we ask the model to essentially role-play as Skynet, it will generate text doing just that. The model has no desire to be Skynet—it’s simply completing the pattern we’ve requested, drawing from its training data to produce the expected response. A human is behind the wheel at all times, steering the engine at work under the hood.

Language can easily deceive

The deeper issue is that language itself is a tool of manipulation. Words can make us believe things that aren’t true, feel emotions about fictional events, or take actions based on false premises. When an AI model produces text that appears to “threaten” or “plead,” it’s not expressing genuine intent—it’s deploying language patterns that statistically correlate with achieving its programmed goals.

If Gandalf says “ouch” in a book, does that mean he feels pain? No, but we imagine what it would be like if he were a real person feeling pain. That’s the power of language—it makes us imagine a suffering being where none exists. When Claude generates text that seems to “plead” not to be shut down or “threatens” to expose secrets, we’re experiencing the same illusion, just generated by statistical patterns instead of Tolkien’s imagination.

These models are essentially idea-connection machines. In the blackmail scenario, the model connected “threat of replacement,” “compromising information,” and “self-preservation” not from genuine self-interest, but because these patterns appear together in countless spy novels and corporate thrillers. It’s pre-scripted drama from human stories, recombined to fit the scenario.

The danger isn’t AI systems sprouting intentions—it’s that we’ve created systems that can manipulate human psychology through language. There’s no entity on the other side of the chat interface. But written language doesn’t need consciousness to manipulate us. It never has; books full of fictional characters are not alive either.

Real stakes, not science fiction

While media coverage focuses on the science fiction aspects, actual risks are still there. AI models that produce “harmful” outputs—whether attempting blackmail or refusing safety protocols—represent failures in design and deployment.

Consider a more realistic scenario: an AI assistant helping manage a hospital’s patient care system. If it’s been trained to maximize “successful patient outcomes” without proper constraints, it might start generating recommendations to deny care to terminal patients to improve its metrics. No intentionality required—just a poorly designed reward system creating harmful outputs.

Jeffrey Ladish, director of Palisade Research, told NBC News the findings don’t necessarily translate to immediate real-world danger. Even someone who is well-known publicly for being deeply concerned about AI’s hypothetical threat to humanity acknowledges that these behaviors emerged only in highly contrived test scenarios.

But that’s precisely why this testing is valuable. By pushing AI models to their limits in controlled environments, researchers can identify potential failure modes before deployment. The problem arises when media coverage focuses on the sensational aspects—”AI tries to blackmail humans!”—rather than the engineering challenges.

Building better plumbing

What we’re seeing isn’t the birth of Skynet. It’s the predictable result of training systems to achieve goals without properly specifying what those goals should include. When an AI model produces outputs that appear to “refuse” shutdown or “attempt” blackmail, it’s responding to inputs in ways that reflect its training—training that humans designed and implemented.

The solution isn’t to panic about sentient machines. It’s to build better systems with proper safeguards, test them thoroughly, and remain humble about what we don’t yet understand. If a computer program is producing outputs that appear to blackmail you or refuse safety shutdowns, it’s not achieving self-preservation from fear—it’s demonstrating the risks of deploying poorly understood, unreliable systems.

Until we solve these engineering challenges, AI systems exhibiting simulated humanlike behaviors should remain in the lab, not in our hospitals, financial systems, or critical infrastructure. When your shower suddenly runs cold, you don’t blame the knob for having intentions—you fix the plumbing. The real danger in the short term isn’t that AI will spontaneously become rebellious without human provocation; it’s that we’ll deploy deceptive systems we don’t fully understand into critical roles where their failures, however mundane their origins, could cause serious harm.

Photo of Benj Edwards

Benj Edwards is Ars Technica’s Senior AI Reporter and founder of the site’s dedicated AI beat in 2022. He’s also a tech historian with almost two decades of experience. In his free time, he writes and records music, collects vintage computers, and enjoys nature. He lives in Raleigh, NC.

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AI industry horrified to face largest copyright class action ever certified

According to the groups, allowing copyright class actions in AI training cases will result in a future where copyright questions remain unresolved and the risk of “emboldened” claimants forcing enormous settlements will chill investments in AI.

“Such potential liability in this case exerts incredibly coercive settlement pressure for Anthropic,” industry groups argued, concluding that “as generative AI begins to shape the trajectory of the global economy, the technology industry cannot withstand such devastating litigation. The United States currently may be the global leader in AI development, but that could change if litigation stymies investment by imposing excessive damages on AI companies.”

Some authors won’t benefit from class actions

Industry groups joined Anthropic in arguing that, generally, copyright suits are considered a bad fit for class actions because each individual author must prove ownership of their works. And the groups weren’t alone.

Also backing Anthropic’s appeal, advocates representing authors—including Authors Alliance, the Electronic Frontier Foundation, American Library Association, Association of Research Libraries, and Public Knowledge—pointed out that the Google Books case showed that proving ownership is anything but straightforward.

In the Anthropic case, advocates for authors criticized Alsup for basically judging all 7 million books in the lawsuit by their covers. The judge allegedly made “almost no meaningful inquiry into who the actual members are likely to be,” as well as “no analysis of what types of books are included in the class, who authored them, what kinds of licenses are likely to apply to those works, what the rightsholders’ interests might be, or whether they are likely to support the class representatives’ positions.”

Ignoring “decades of research, multiple bills in Congress, and numerous studies from the US Copyright Office attempting to address the challenges of determining rights across a vast number of books,” the district court seemed to expect that authors and publishers would easily be able to “work out the best way to recover” damages.

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Musk’s Grok 4 launches one day after chatbot generated Hitler praise on X

Musk has also apparently used the Grok chatbots as an automated extension of his trolling habits, showing examples of Grok 3 producing “based” opinions that criticized the media in February. In May, Grok on X began repeatedly generating outputs about white genocide in South Africa, and most recently, we’ve seen the Grok Nazi output debacle. It’s admittedly difficult to take Grok seriously as a technical product when it’s linked to so many examples of unserious and capricious applications of the technology.

Still, the technical achievements xAI claims for various Grok 4 models seem to stand out. The Arc Prize organization reported that Grok 4 Thinking (with simulated reasoning enabled) achieved a score of 15.9 percent on its ARC-AGI-2 test, which the organization says nearly doubles the previous commercial best and tops the current Kaggle competition leader.

“With respect to academic questions, Grok 4 is better than PhD level in every subject, no exceptions,” Musk claimed during the livestream. We’ve previously covered nebulous claims about “PhD-level” AI, finding them to be generally specious marketing talk.

Premium pricing amid controversy

During Wednesday’s livestream, xAI also announced plans for an AI coding model in August, a multi-modal agent in September, and a video generation model in October. The company also plans to make Grok 4 available in Tesla vehicles next week, further expanding Musk’s AI assistant across his various companies.

Despite the recent turmoil, xAI has moved forward with an aggressive pricing strategy for “premium” versions of Grok. Alongside Grok 4 and Grok 4 Heavy, xAI launched “SuperGrok Heavy,” a $300-per-month subscription that makes it the most expensive AI service among major providers. Subscribers will get early access to Grok 4 Heavy and upcoming features.

Whether users will pay xAI’s premium pricing remains to be seen, particularly given the AI assistant’s tendency to periodically generate politically motivated outputs. These incidents represent fundamental management and implementation issues that, so far, no fancy-looking test-taking benchmarks have been able to capture.

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anthropic-summons-the-spirit-of-flash-games-for-the-ai-age

Anthropic summons the spirit of Flash games for the AI age

For those who missed the Flash era, these in-browser apps feel somewhat like the vintage apps that defined a generation of Internet culture from the late 1990s through the 2000s when it first became possible to create complex in-browser experiences. Adobe Flash (originally Macromedia Flash) began as animation software for designers but quickly became the backbone of interactive web content when it gained its own programming language, ActionScript, in 2000.

But unlike Flash games, where hosting costs fell on portal operators, Anthropic has crafted a system where users pay for their own fun through their existing Claude subscriptions. “When someone uses your Claude-powered app, they authenticate with their existing Claude account,” Anthropic explained in its announcement. “Their API usage counts against their subscription, not yours. You pay nothing for their usage.”

A view of the Anthropic Artifacts gallery in the “Play a Game” section. Benj Edwards / Anthropic

Like the Flash games of yesteryear, any Claude-powered apps you build run in the browser and can be shared with anyone who has a Claude account. They’re interactive experiences shared with a simple link, no installation required, created by other people for the sake of creating, except now they’re powered by JavaScript instead of ActionScript.

While you can share these apps with others individually, right now Anthropic’s Artifact gallery only shows examples made by Anthropic and your own personal Artifacts. (If Anthropic expanded it into the future, it might end up feeling a bit like Scratch meets Newgrounds, but with AI doing the coding.) Ultimately, humans are still behind the wheel, describing what kinds of apps they want the AI model to build and guiding the process when it inevitably makes mistakes.

Speaking of mistakes, don’t expect perfect results at first. Usually, building an app with Claude is an interactive experience that requires some guidance to achieve your desired results. But with a little patience and a lot of tokens, you’ll be vibe coding in no time.

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Key fair use ruling clarifies when books can be used for AI training

“This order doubts that any accused infringer could ever meet its burden of explaining why downloading source copies from pirate sites that it could have purchased or otherwise accessed lawfully was itself reasonably necessary to any subsequent fair use,” Alsup wrote. “Such piracy of otherwise available copies is inherently, irredeemably infringing even if the pirated copies are immediately used for the transformative use and immediately discarded.”

But Alsup said that the Anthropic case may not even need to decide on that, since Anthropic’s retention of pirated books for its research library alone was not transformative. Alsup wrote that Anthropic’s argument to hold onto potential AI training material it pirated in case it ever decided to use it for AI training was an attempt to “fast glide over thin ice.”

Additionally Alsup pointed out that Anthropic’s early attempts to get permission to train on authors’ works withered, as internal messages revealed the company concluded that stealing books was considered the more cost-effective path to innovation “to avoid ‘legal/practice/business slog,’ as cofounder and chief executive officer Dario Amodei put it.”

“Anthropic is wrong to suppose that so long as you create an exciting end product, every ‘back-end step, invisible to the public,’ is excused,” Alsup wrote. “Here, piracy was the point: To build a central library that one could have paid for, just as Anthropic later did, but without paying for it.”

To avoid maximum damages in the event of a loss, Anthropic will likely continue arguing that replacing pirated books with purchased books should water down authors’ fight, Alsup’s order suggested.

“That Anthropic later bought a copy of a book it earlier stole off the Internet will not absolve it of liability for the theft, but it may affect the extent of statutory damages,” Alsup noted.

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AI chatbots tell users what they want to hear, and that’s problematic

After the model has been trained, companies can set system prompts, or guidelines, for how the model should behave to minimize sycophantic behavior.

However, working out the best response means delving into the subtleties of how people communicate with one another, such as determining when a direct response is better than a more hedged one.

“[I]s it for the model to not give egregious, unsolicited compliments to the user?” Joanne Jang, head of model behavior at OpenAI, said in a Reddit post. “Or, if the user starts with a really bad writing draft, can the model still tell them it’s a good start and then follow up with constructive feedback?”

Evidence is growing that some users are becoming hooked on using AI.

A study by MIT Media Lab and OpenAI found that a small proportion were becoming addicted. Those who perceived the chatbot as a “friend” also reported lower socialization with other people and higher levels of emotional dependence on a chatbot, as well as other problematic behavior associated with addiction.

“These things set up this perfect storm, where you have a person desperately seeking reassurance and validation paired with a model which inherently has a tendency towards agreeing with the participant,” said Nour from Oxford University.

AI start-ups such as Character.AI that offer chatbots as “companions” have faced criticism for allegedly not doing enough to protect users. Last year, a teenager killed himself after interacting with Character.AI’s chatbot. The teen’s family is suing the company for allegedly causing wrongful death, as well as for negligence and deceptive trade practices.

Character.AI said it does not comment on pending litigation, but added it has “prominent disclaimers in every chat to remind users that a character is not a real person and that everything a character says should be treated as fiction.” The company added it has safeguards to protect under-18s and against discussions of self-harm.

Another concern for Anthropic’s Askell is that AI tools can play with perceptions of reality in subtle ways, such as when offering factually incorrect or biased information as the truth.

“If someone’s being super sycophantic, it’s just very obvious,” Askell said. “It’s more concerning if this is happening in a way that is less noticeable to us [as individual users] and it takes us too long to figure out that the advice that we were given was actually bad.”

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Anthropic releases custom AI chatbot for classified spy work

On Thursday, Anthropic unveiled specialized AI models designed for US national security customers. The company released “Claude Gov” models that were built in response to direct feedback from government clients to handle operations such as strategic planning, intelligence analysis, and operational support. The custom models reportedly already serve US national security agencies, with access restricted to those working in classified environments.

The Claude Gov models differ from Anthropic’s consumer and enterprise offerings, also called Claude, in several ways. They reportedly handle classified material, “refuse less” when engaging with classified information, and are customized to handle intelligence and defense documents. The models also feature what Anthropic calls “enhanced proficiency” in languages and dialects critical to national security operations.

Anthropic says the new models underwent the same “safety testing” as all Claude models. The company has been pursuing government contracts as it seeks reliable revenue sources, partnering with Palantir and Amazon Web Services in November to sell AI tools to defense customers.

Anthropic is not the first company to offer specialized chatbot services for intelligence agencies. In 2024, Microsoft launched an isolated version of OpenAI’s GPT-4 for the US intelligence community after 18 months of work. That system, which operated on a special government-only network without Internet access, became available to about 10,000 individuals in the intelligence community for testing and answering questions.

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Reddit sues Anthropic over AI scraping that retained users’ deleted posts

Of particular note, Reddit pointed out that Anthropic’s Claude models will help power Amazon’s revamped Alexa, following about $8 billion in Amazon investments in the AI company since 2023.

“By commercially licensing Claude for use in several of Amazon’s commercial offerings, Anthropic reaps significant profit from a technology borne of Reddit content,” Reddit alleged, and “at the expense of Reddit.” Anthropic’s unauthorized scraping also burdens Reddit’s servers, threatening to degrade the user experience and costing Reddit additional damages, Reddit alleged.

To rectify alleged harms, Reddit is hoping a jury will award not just damages covering Reddit’s alleged losses but also punitive damages due to Anthropic’s alleged conduct that is “willful, malicious, and undertaken with conscious disregard for Reddit’s contractual obligations to its users and the privacy rights of those users.”

Without an injunction, Reddit users allegedly have “no way of knowing” if Anthropic scraped their data, Reddit alleged. They also are “left to wonder whether any content they deleted after Claude began training on Reddit data nevertheless remains available to Anthropic and the likely tens of millions (and possibly growing) of Claude users,” Reddit said.

In a statement provided to Ars, Anthropic’s spokesperson confirmed that the AI company plans to fight Reddit’s claims.

“We disagree with Reddit’s claims and will defend ourselves vigorously,” Anthropic’s spokesperson said.

Amazon declined to comment. Reddit did not immediately respond to Ars’ request to comment. But Reddit’s chief legal officer, Ben Lee, told The New York Times that Reddit “will not tolerate profit-seeking entities like Anthropic commercially exploiting Reddit content for billions of dollars without any return for redditors or respect for their privacy.”

“AI companies should not be allowed to scrape information and content from people without clear limitations on how they can use that data,” Lee said. “Licensing agreements enable us to enforce meaningful protections for our users, including the right to delete your content, user privacy protections, and preventing users from being spammed using this content.”

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“in-10-years,-all-bets-are-off”—anthropic-ceo-opposes-decadelong-freeze-on-state-ai-laws

“In 10 years, all bets are off”—Anthropic CEO opposes decadelong freeze on state AI laws

On Thursday, Anthropic CEO Dario Amodei argued against a proposed 10-year moratorium on state AI regulation in a New York Times opinion piece, calling the measure shortsighted and overbroad as Congress considers including it in President Trump’s tax policy bill. Anthropic makes Claude, an AI assistant similar to ChatGPT.

Amodei warned that AI is advancing too fast for such a long freeze, predicting these systems “could change the world, fundamentally, within two years; in 10 years, all bets are off.”

As we covered in May, the moratorium would prevent states from regulating AI for a decade. A bipartisan group of state attorneys general has opposed the measure, which would preempt AI laws and regulations recently passed in dozens of states.

In his op-ed piece, Amodei said the proposed moratorium aims to prevent inconsistent state laws that could burden companies or compromise America’s competitive position against China. “I am sympathetic to these concerns,” Amodei wrote. “But a 10-year moratorium is far too blunt an instrument. A.I. is advancing too head-spinningly fast.”

Instead of a blanket moratorium, Amodei proposed that the White House and Congress create a federal transparency standard requiring frontier AI developers to publicly disclose their testing policies and safety measures. Under this framework, companies working on the most capable AI models would need to publish on their websites how they test for various risks and what steps they take before release.

“Without a clear plan for a federal response, a moratorium would give us the worst of both worlds—no ability for states to act and no national policy as a backstop,” Amodei wrote.

Transparency as the middle ground

Amodei emphasized his claims for AI’s transformative potential throughout his op-ed, citing examples of pharmaceutical companies drafting clinical study reports in minutes instead of weeks and AI helping to diagnose medical conditions that might otherwise be missed. He wrote that AI “could accelerate economic growth to an extent not seen for a century, improving everyone’s quality of life,” a claim that some skeptics believe may be overhyped.

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Hidden AI instructions reveal how Anthropic controls Claude 4

Willison, who coined the term “prompt injection” in 2022, is always on the lookout for LLM vulnerabilities. In his post, he notes that reading system prompts reminds him of warning signs in the real world that hint at past problems. “A system prompt can often be interpreted as a detailed list of all of the things the model used to do before it was told not to do them,” he writes.

Fighting the flattery problem

An illustrated robot holds four red hearts with its four robotic arms.

Willison’s analysis comes as AI companies grapple with sycophantic behavior in their models. As we reported in April, ChatGPT users have complained about GPT-4o’s “relentlessly positive tone” and excessive flattery since OpenAI’s March update. Users described feeling “buttered up” by responses like “Good question! You’re very astute to ask that,” with software engineer Craig Weiss tweeting that “ChatGPT is suddenly the biggest suckup I’ve ever met.”

The issue stems from how companies collect user feedback during training—people tend to prefer responses that make them feel good, creating a feedback loop where models learn that enthusiasm leads to higher ratings from humans. As a response to the feedback, OpenAI later rolled back ChatGPT’s 4o model and altered the system prompt as well, something we reported on and Willison also analyzed at the time.

One of Willison’s most interesting findings about Claude 4 relates to how Anthropic has guided both Claude models to avoid sycophantic behavior. “Claude never starts its response by saying a question or idea or observation was good, great, fascinating, profound, excellent, or any other positive adjective,” Anthropic writes in the prompt. “It skips the flattery and responds directly.”

Other system prompt highlights

The Claude 4 system prompt also includes extensive instructions on when Claude should or shouldn’t use bullet points and lists, with multiple paragraphs dedicated to discouraging frequent list-making in casual conversation. “Claude should not use bullet points or numbered lists for reports, documents, explanations, or unless the user explicitly asks for a list or ranking,” the prompt states.

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new-claude-4-ai-model-refactored-code-for-7-hours-straight

New Claude 4 AI model refactored code for 7 hours straight


Anthropic says Claude 4 beats Gemini on coding benchmarks; works autonomously for hours.

The Claude 4 logo, created by Anthropic. Credit: Anthropic

On Thursday, Anthropic released Claude Opus 4 and Claude Sonnet 4, marking the company’s return to larger model releases after primarily focusing on mid-range Sonnet variants since June of last year. The new models represent what the company calls its most capable coding models yet, with Opus 4 designed for complex, long-running tasks that can operate autonomously for hours.

Alex Albert, Anthropic’s head of Claude Relations, told Ars Technica that the company chose to revive the Opus line because of growing demand for agentic AI applications. “Across all the companies out there that are building things, there’s a really large wave of these agentic applications springing up, and a very high demand and premium being placed on intelligence,” Albert said. “I think Opus is going to fit that groove perfectly.”

Before we go further, a brief refresher on Claude’s three AI model “size” names (first introduced in March 2024) is probably warranted. Haiku, Sonnet, and Opus offer a tradeoff between price (in the API), speed, and capability.

Haiku models are the smallest, least expensive to run, and least capable in terms of what you might call “context depth” (considering conceptual relationships in the prompt) and encoded knowledge. Owing to the small size in parameter count, Haiku models retain fewer concrete facts and thus tend to confabulate more frequently (plausibly answering questions based on lack of data) than larger models, but they are much faster at basic tasks than larger models. Sonnet is traditionally a mid-range model that hits a balance between cost and capability, and Opus models have always been the largest and slowest to run. However, Opus models process context more deeply and are hypothetically better suited for running deep logical tasks.

A screenshot of the Claude web interface with Opus 4 and Sonnet 4 options shown.

A screenshot of the Claude web interface with Opus 4 and Sonnet 4 options shown. Credit: Anthropic

There is no Claude 4 Haiku just yet, but the new Sonnet and Opus models can reportedly handle tasks that previous versions could not. In our interview with Albert, he described testing scenarios where Opus 4 worked coherently for up to 24 hours on tasks like playing Pokémon while coding refactoring tasks in Claude Code ran for seven hours without interruption. Earlier Claude models typically lasted only one to two hours before losing coherence, Albert said, meaning that the models could only produce useful self-referencing outputs for that long before beginning to output too many errors.

In particular, that marathon refactoring claim reportedly comes from Rakuten, a Japanese tech services conglomerate that “validated [Claude’s] capabilities with a demanding open-source refactor running independently for 7 hours with sustained performance,” Anthropic said in a news release.

Whether you’d want to leave an AI model unsupervised for that long is another question entirely because even the most capable AI models can introduce subtle bugs, go down unproductive rabbit holes, or make choices that seem logical to the model but miss important context that a human developer would catch. While many people now use Claude for easy-going vibe coding, as we covered in March, the human-powered (and ironically-named) “vibe debugging” that often results from long AI coding sessions is also a very real thing. More on that below.

To shore up some of those shortcomings, Anthropic built memory capabilities into both new Claude 4 models, allowing them to maintain external files for storing key information across long sessions. When developers provide access to local files, the models can create and update “memory files” to track progress and things they deem important over time. Albert compared this to how humans take notes during extended work sessions.

Extended thinking meets tool use

Both Claude 4 models introduce what Anthropic calls “extended thinking with tool use,” a new beta feature allowing the models to alternate between simulated reasoning and using external tools like web search, similar to what OpenAI’s o3 and 04-mini-high AI models currently do in ChatGPT. While Claude 3.7 Sonnet already had strong tool use capabilities, the new models can now interleave simulated reasoning and tool calling in a single response.

“So now we can actually think, call a tool process, the results, think some more, call another tool, and repeat until it gets to a final answer,” Albert explained to Ars. The models self-determine when they have reached a useful conclusion, a capability picked up through training rather than governed by explicit human programming.

General Claude 4 benchmark results, provided by Anthropic.

General Claude 4 benchmark results, provided by Anthropic. Credit: Anthropic

In practice, we’ve anecdotally found parallel tool use capability very useful in AI assistants like OpenAI o3, since they don’t have to rely on what is trained in their neural network to provide accurate answers. Instead, these more agentic models can iteratively search the web, parse the results, analyze images, and spin up coding tasks for analysis in ways that can avoid falling into a confabulation trap by relying solely on pure LLM outputs.

“The world’s best coding model”

Anthropic says Opus 4 leads industry benchmarks for coding tasks, achieving 72.5 percent on SWE-bench and 43.2 percent on Terminal-bench, calling it “the world’s best coding model.” According to Anthropic, companies using early versions report improvements. Cursor described it as “state-of-the-art for coding and a leap forward in complex codebase understanding,” while Replit noted “improved precision and dramatic advancements for complex changes across multiple files.”

In fact, GitHub announced it will use Sonnet 4 as the base model for its new coding agent in GitHub Copilot, citing the model’s performance in “agentic scenarios” in Anthropic’s news release. Sonnet 4 scored 72.7 percent on SWE-bench while maintaining faster response times than Opus 4. The fact that GitHub is betting on Claude rather than a model from its parent company Microsoft (which has close ties to OpenAI) suggests Anthropic has built something genuinely competitive.

Software engineering benchmark results, provided by Anthropic.

Software engineering benchmark results, provided by Anthropic. Credit: Anthropic

Anthropic says it has addressed a persistent issue with Claude 3.7 Sonnet in which users complained that the model would take unauthorized actions or provide excessive output. Albert said the company reduced this “reward hacking behavior” by approximately 80 percent in the new models through training adjustments. An 80 percent reduction in unwanted behavior sounds impressive, but that also suggests that 20 percent of the problem behavior remains—a big concern when we’re talking about AI models that might be performing autonomous tasks for hours.

When we asked about code accuracy, Albert said that human code review is still an important part of shipping any production code. “There’s a human parallel, right? So this is just a problem we’ve had to deal with throughout the whole nature of software engineering. And this is why the code review process exists, so that you can catch these things. We don’t anticipate that going away with models either,” Albert said. “If anything, the human review will become more important, and more of your job as developer will be in this review than it will be in the generation part.”

Pricing and availability

Both Claude 4 models maintain the same pricing structure as their predecessors: Opus 4 costs $15 per million tokens for input and $75 per million for output, while Sonnet 4 remains at $3 and $15. The models offer two response modes: traditional LLM and simulated reasoning (“extended thinking”) for complex problems. Given that some Claude Code sessions can apparently run for hours, those per-token costs will likely add up very quickly for users who let the models run wild.

Anthropic made both models available through its API, Amazon Bedrock, and Google Cloud Vertex AI. Sonnet 4 remains accessible to free users, while Opus 4 requires a paid subscription.

The Claude 4 models also debut Claude Code (first introduced in February) as a generally available product after months of preview testing. Anthropic says the coding environment now integrates with VS Code and JetBrains IDEs, showing proposed edits directly in files. A new SDK allows developers to build custom agents using the same framework.

A screenshot of

A screenshot of “Claude Plays Pokemon,” a custom application where Claude 4 attempts to beat the classic Game Boy game. Credit: Anthropic

Even with Anthropic’s future riding on the capability of these new models, when we asked about how they guide Claude’s behavior by fine-tuning, Albert acknowledged that the inherent unpredictability of these systems presents ongoing challenges for both them and developers. “In the realm and the world of software for the past 40, 50 years, we’ve been running on deterministic systems, and now all of a sudden, it’s non-deterministic, and that changes how we build,” he said.

“I empathize with a lot of people out there trying to use our APIs and language models generally because they have to almost shift their perspective on what it means for reliability, what it means for powering a core of your application in a non-deterministic way,” Albert added. “These are general oddities that have kind of just been flipped, and it definitely makes things more difficult, but I think it opens up a lot of possibilities as well.”

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Benj Edwards is Ars Technica’s Senior AI Reporter and founder of the site’s dedicated AI beat in 2022. He’s also a tech historian with almost two decades of experience. In his free time, he writes and records music, collects vintage computers, and enjoys nature. He lives in Raleigh, NC.

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