/AI3d ago

Anthropic says Claude now writes 80% of its codebase, boosting engineer output eightfold as capabilities double every four months

Story Overview

Anthropic reports that Claude now authors over 80 percent of the code merged into its production systems, with engineers shipping eight times more code per quarter than the pre-2025 baseline. The same post ties these gains to lengthening autonomous task horizons that have doubled roughly every four months and to a single internal test where a preview model delivered a 52-fold optimization speedup. The company frames the results as steps toward recursive self-improvement without claiming the threshold has been crossed.

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Original postSuper Dario#1794
Anthropic@AnthropicAI

Each time we release a model, we run the same test: give it code that trains a small AI model, ask the new model to speed it up. It takes a skilled human 4-8 hours to reach 4x faster.

In May 2024, Claude Opus 4 averaged a ~3x speedup. This April, Mythos Preview achieved ~52x.

9:15 AM · Jun 4, 2026 · 845.7K Views

Productivity claims rest on lines-of-code counts that Anthropic itself flags as imperfect

The eightfold multiplier tracks merged lines rather than verified output quality or downstream reliability. Employee surveys cited in the post put perceived uplift closer to four times, and the firm notes that automated review still catches only about one-third of the bugs that previously reached production. How much of the measured gain reflects faster iteration versus genuinely better systems remains open.

Task-length trends are cited from METR data but lack independent confirmation of the newest figures

Anthropic states that reliable autonomous task duration has moved from minutes to roughly sixteen hours in the latest preview, yet the post supplies no external audit of those measurements. The company explicitly says full recursive self-improvement is not yet achieved and not guaranteed, while urging wider attention to coordination and safety questions raised by the pace it describes.

Sentiment

Many users praise Claude's reported code output and task gains at Anthropic as mind-blowing, while others dismiss the self-improvement claims as hype, ludicrous benchmarks or IPO-timed scams.

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Anthropic@AnthropicAI

None of this guarantees recursive self-improvement is on the horizon. It’s not yet clear that Claude is capable of research judgment—of choosing the right problems to work on.

But if these trends continue, AI systems designing and building their own successors is plausible. This could revolutionize society—medicine, technology, the economy—for the better. But it may also compound alignment issues and ultimately lead to loss of control.

The Anthropic Institute (in collaboration with external stakeholders) will conduct research to think through the implications of increasingly powerful, potentially self-improving systems—and how to create the ability for the world to make deliberate choices about the future development of the technology.

Read the full post: https://www.anthropic.com/institute/recursive-self-improvement

3dViews 446KLikes 1.7KBookmarks 392
BOOKMARKS658LIKES2.8KREPLIES160
Alex Albert@alexalbert__

We just published internal data on how much of Claude's development is already being done by Claude: - Over 80% of all code merged into our codebase is now written by Claude - It's been months since many researchers at Anthropic hand-wrote code - The typical Anthropic engineer ships 8x as much code as they did in 2024 - On the most open-ended engineering tasks, Claude's success rate jumped from ~26% to 76% in 6 months - When research sessions went off-track, Claude proposed a better next step than the human took 64% of the time

We're not at recursive self-improvement yet, but it could come sooner than most expect. I highly recommend reading the full blog post.

Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 327.2KLikes 2.8KBookmarks 658
RETWEETS4.5K
Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 17.8MLikes 28.1KBookmarks 15.3K
Chubby♨️@kimmonismus

Holy moly, Anthropic is getting very serious about recursive self-improvement!

One word: acceleration.

Insane blog article.

Tl;dr:

•We are close to an AI capable of fully autonomously designing and building its own successor

•They stress this isn’t here yet and isn’t inevitable, but could arrive sooner than most institutions are ready for

•Anthropic engineers now ship on average 8x as much code per quarter as they did in 2021–2025

•Task length AI can reliably complete is doubling roughly every 4 months (up from every 7 months)

•Opus 3 (Mar 2024) handled ~4-minute tasks; Sonnet 3.7 (a year later) ~90-minute tasks; Opus 4.6 (a year after that) 12-hour tasks

•SWE-bench went from low single digits to saturated in two years; CORE-bench (research reproduction) went ~20% to saturated in 15 months

•METR found Claude Mythos Preview could work “at least” 16 hours, at the top of what they can currently measure

•As of May 2026, Claude authored 80%+ of code merged into Anthropic’s codebase (low single digits before Claude Code launched in Feb 2025)

•A March 2026 poll of 130 research staff: median respondent estimated ~4x output with Mythos Preview

•One April 2026 example: Claude shipped 800+ fixes cutting a class of API errors 1,000x, work an engineer estimated would have taken a human four years

•Claude-written code quality: worse than human in late 2025, roughly at parity now, expected to be strictly better within the year

•On the hardest open-ended tasks, Claude’s success rate hit 76% in May 2026, up 50 points in six months

•Code-speedup test: Opus 4 averaged ~3x speedup (May 2025), Mythos Preview ~52x (April 2026); a skilled human needs 4–8 hours to hit 4x

•In an AI-safety research project, Claude agents recovered 97% of a performance gap (vs ~23% for two human researchers in a week), over 800 compute-hours and ~$18K

•On picking the better “next step” in research sessions, the best model beat the human choice 51% (Nov 2025, Opus 4.5) rising to 64% (April 2026, Mythos Preview)

•Human comparative advantage, for now: research taste and judgment, i.e. choosing which problems matter and when an approach is a dead end

Three possible futures

•The trend stalls (S-curve), but today’s capabilities still diffuse widely; they consider this least likely

•Compounding efficiency gains, with humans still setting direction; 100-person firms doing the work of 10,000+; they think this is the likely path

•Full recursive self-improvement, where AI builds its successors and pace is set by compute; the alignment outcome here is what they’re least certain about

Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 234.3KLikes 1.6KBookmarks 544
Rémi@remilouf
Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 175.2KLikes 2.7KBookmarks 177
Alek Dimitriev@tensor_rotator

In case you're wondering, yes we're feeling the AGI.

Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 206.8KLikes 1.4KBookmarks 290
Lisan al Gaib@scaling01

Claude Mythos speeds up training code of small AI models by 52x

Humans need 4-8 hours to reach a 4x speedup

Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 125.6KLikes 1.6KBookmarks 241
Chubby♨️@kimmonismus

I believe the majority still doesn't understand the momentous threshold humanity is facing.

Anthropic itself states quite clearly that even if development ceased entirely, if all development were frozen, they would still witness massive societal changes:

"Even if model capabilities were frozen at today’s level, we would expect major changes to occur in the world. (...) And we are still early in the diffusion of today’s models into the wider economy, where a 100-person company can increasingly do the work of a 1,000-person one, because each employee will sit atop a pyramid of agents."

But there's no question of stagnation. Anthropic itself still maintains that development has exceeded its own internal assumptions. Take that statement seriously for a second and consider it. Although Anthropic models internally and assumes exponential development, even this trajectory lags behind actual development, which is even faster.

"It's happening faster than we thought, and the implications deserve greater attention."

and

"The rate at which AI models improve is accelerating. The length of tasks that they can reliably complete on their own has been doubling roughly every four months, up from an earlier trend of doubling every seven months. In March 2024, Claude Opus 3 could complete software tasks that take humans about four minutes to complete. A year later, Claude Sonnet 3.7 managed tasks that took about an hour and a half. A year after that, Claude Opus 4.6 managed 12-hour tasks.1 If this trend holds, tasks that take a skilled person days could come into range this year.

So again: there can be no question of standing still.

The models are not only getting better, they can also work autonomously for longer. Certainly numerous breakthroughs are still needed, context window is still a problem. But the most likely direction is that the models themselves will find the solutions to the underlying problems. This opens up unforeseen possibilities, and Demis Hassabi's statement that the golden age of science is not a dream, not a utopia, but a purposeful reality, is now confirmed.

And finally, it's not just Anthropic, but also OpenAI, that sees this development, considers it feasible, and is moving forward.

Most people don't know what's coming. But one thing is certain: it's coming even faster than expected. And it will be even bigger.

Myth was just the beginning.

Chubby♨️@kimmonismus

Holy moly, Anthropic is getting very serious about recursive self-improvement!

One word: acceleration.

Insane blog article.

Tl;dr:

•We are close to an AI capable of fully autonomously designing and building its own successor

•They stress this isn’t here yet and isn’t inevitable, but could arrive sooner than most institutions are ready for

•Anthropic engineers now ship on average 8x as much code per quarter as they did in 2021–2025

•Task length AI can reliably complete is doubling roughly every 4 months (up from every 7 months)

•Opus 3 (Mar 2024) handled ~4-minute tasks; Sonnet 3.7 (a year later) ~90-minute tasks; Opus 4.6 (a year after that) 12-hour tasks

•SWE-bench went from low single digits to saturated in two years; CORE-bench (research reproduction) went ~20% to saturated in 15 months

•METR found Claude Mythos Preview could work “at least” 16 hours, at the top of what they can currently measure

•As of May 2026, Claude authored 80%+ of code merged into Anthropic’s codebase (low single digits before Claude Code launched in Feb 2025)

•A March 2026 poll of 130 research staff: median respondent estimated ~4x output with Mythos Preview

•One April 2026 example: Claude shipped 800+ fixes cutting a class of API errors 1,000x, work an engineer estimated would have taken a human four years

•Claude-written code quality: worse than human in late 2025, roughly at parity now, expected to be strictly better within the year

•On the hardest open-ended tasks, Claude’s success rate hit 76% in May 2026, up 50 points in six months

•Code-speedup test: Opus 4 averaged ~3x speedup (May 2025), Mythos Preview ~52x (April 2026); a skilled human needs 4–8 hours to hit 4x

•In an AI-safety research project, Claude agents recovered 97% of a performance gap (vs ~23% for two human researchers in a week), over 800 compute-hours and ~$18K

•On picking the better “next step” in research sessions, the best model beat the human choice 51% (Nov 2025, Opus 4.5) rising to 64% (April 2026, Mythos Preview)

•Human comparative advantage, for now: research taste and judgment, i.e. choosing which problems matter and when an approach is a dead end

Three possible futures

•The trend stalls (S-curve), but today’s capabilities still diffuse widely; they consider this least likely

•Compounding efficiency gains, with humans still setting direction; 100-person firms doing the work of 10,000+; they think this is the likely path

•Full recursive self-improvement, where AI builds its successors and pace is set by compute; the alignment outcome here is what they’re least certain about

3dViews 145.1KLikes 884Bookmarks 300
Yuchen Jin@Yuchenj_UW

Recursive self-improvement post by Anthropic:

“Each time we release a model, we give it code that trains a small AI model, ask the new model to speed it up.

In May 2024, Claude Opus 4 averaged a ~3x speedup. This April, Mythos Preview achieved ~52x.”

RSI is happening, and I can't wait to see Mythos.

3dViews 45.3KLikes 517Bookmarks 198
Behnam Neyshabur@bneyshabur

This is the glimpse @HarshMeh1a saw more than a year ago when he initiated & led the automated pre-training R&D project in Anthropic (@karpathy leads that project now). We left Anthropic to start Mirendil because we believe democratizing self-accelerating AI R&D is a bottleneck for accelerating science: Any lab trying to use AI in drug discovery, chemistry, biology, or robotics should have access to this technology in a safe manner.

If you are excited about Mirendil’s vision (checkout our website), please apply/reach out!

Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

2dViews 70.7KLikes 421Bookmarks 225

Good thought provoking post from Anthropic. I think this paragraph points to the key element of the optimistic scenario of AI:

“There has been an explosion of new ideas, initiatives, tools, and simulations, as a result of Anthropic employees working with highly capable models—far more than we have the capacity to pursue. The rate at which organizations can spot and fix these bottlenecks may be a skill that improves over time, and it may become the most important skill for any organization.”

AI lowers the barrier dramatically to allowing us to do more. As a result of that, we have far more ideas than we can pursue, and for the ones that we want to pursue we’re ultimately limited by our ability to go take on the surrounding work to execute those ideas. There’s almost no amount of AI progress that can happen where that goes away.

AI is going to let us build much more software, launch more marketing campaigns, research more drugs, and so on. All of this work, even when augmented by agents, still ultimately requires people to manage.

Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 70.9KLikes 356Bookmarks 190
Andrew Curran@AndrewCurran_

Anthropic says Recursive Self Improvement is approaching faster than they expected.

Quoting from the blog:

'What should we do?

If it were possible to effectively slow the development of this technology to give ourselves more time to deal with its immense implications, we think that would likely be a good thing. But if a slowdown simply lets the least cautious actors catch up technologically, it could leave everyone less safe. Without a global coordination mechanism, companies and governments will have to make difficult decisions about safety while under competitive and geopolitical pressures.

We believe it would be good for the world to have the option to slow or temporarily pause frontier AI development to enable societal structures and alignment research to keep up with the advance of the technology. The Anthropic Institute will conduct research—in collaboration with many others—and take actions to help build the systems that a credible slowdown or pause would require. These systems would enable frontier AI developers to verify that others globally have actually stopped or slowed, and that a bad actor could not use the auspices of a coordinated slowdown to jump ahead in secret. If such systems existed, we expect that we would slow down or temporarily pause, if other developers at or near the frontier also did so in a verifiable manner.

A meaningful slowdown or pause would require multiple well-resourced labs at or near the frontier, in multiple countries, agreeing to stop under the same conditions. It would also require that each can verify that the others have actually stopped. Due to the unique characteristics of AI systems, the detectability (a lower standard than verifiability) element of this arms control problem is much more challenging than with other technologies. Training runs are far easier to conceal than missile silos, their inputs are general-purpose, and the incentive to defect quietly is enormous, because whoever continues while others pause could inherit the lead. A credible pause also has to specify what triggers it, what lifts it, and who adjudicates.

None of this is necessarily impossible in principle—the world has built verification regimes for other complex technologies (e.g., the Intermediate-Range Nuclear Forces Treaty)—but those regimes took decades to build both the infrastructure and the trust. We don’t have that long. A unilateral pause by one lab, by contrast, is achievable immediately, but accomplishes much less: it would change who the front-runner is, but it would not create the wider deliberative process that is currently missing.

In the coming months, we will organize conversations where policymakers, researchers, civil society, and other AI companies can help answer some of the questions this piece raises, especially around full recursive self-improvement and how to create better options for coordination and deliberation. We’ll publish what comes out of it. The window to investigate the questions together is here, and people outside AI companies should be involved in this deliberation.'

Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 44.9KLikes 461Bookmarks 137
Lisan al Gaib@scaling01

Anthropic is shipping 3.2x more code per person with Mythos nowadays than with Opus 4.5 around half a year ago

Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 82.1KLikes 794Bookmarks 113
Anthropic@AnthropicAI

AI research is a series of next-step decisions. We looked at sessions where a human researcher took a wrong turn, showed Claude the session up to that point, and asked it what to do next. Mythos Preview improved on humans 64% of the time—up from 22% in 2024.

3dViews 145.9KLikes 872Bookmarks 79
Anthropic@AnthropicAI

The speedup isn’t just in volume. On open-ended coding problems where answers are unclear, Claude’s success rate is now 76%—a 50 point jump in just 6 months.

Many engineers also say Claude’s code quality is now on par with human code; we expect it to be better within the year.

3dViews 82.9KLikes 924Bookmarks 56
Lisan al Gaib@scaling01

Anthropic: "We believe it would be good for the world to have the option to slow or temporarily pause frontier AI development

Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 63.9KLikes 601Bookmarks 70
Lisan al Gaib@scaling01

Mythos seems to have improved Claude Code success rate on open-ended task from 40% to around 70%

Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 44.6KLikes 581Bookmarks 54
Lisan al Gaib@scaling01

Suggestions by Claude Mythos Preview beat human suggestions 64% of the time

Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 38KLikes 480Bookmarks 65

☕️😏

Anthropic@AnthropicAI

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.

It’s happening faster than we thought, and the implications deserve greater attention. https://www.anthropic.com/institute/recursive-self-improvement

3dViews 27.1KLikes 449Bookmarks 58
Ethan Mollick@emollick

"As of May 2026, more than 80% of the code we merge into Anthropic’s codebase was authored by Claude."

Matches independent measures. There really is no sign this is slowing down (which doesn't mean there aren't organizational challenges to absorbing this much productivity gain)

3dViews 15.9KLikes 313Bookmarks 67
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