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Claude (language model)

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Claude
DeveloperAnthropic
Initial releaseMarch 2023; 2 years ago (2023-03)
Stable release
Claude Opus 4.5 /
November 24, 2025; 2 months ago (2025-11-24)
Claude Sonnet 4.5 /
September 29, 2025; 4 months ago (2025-09-29)
Claude Haiku 4.5 /
October 15, 2025; 3 months ago (2025-10-15)
PlatformCloud computing platforms
Type
LicenseProprietary
Websiteclaude.ai

Claude is a series of large language models developed by Anthropic. The first model was released in March 2023, and the latest, Claude Opus 4.5, in November 2025.

Training

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See also: Anthropic § Legal issues

Claude models are generative pre-trained transformers that have been pre-trained to predict the next word in large amounts of text. Then, they have been fine-tuned, notably using constitutional AI and reinforcement learning from human feedback (RLHF).[1][2] ClaudeBot searches the web for content. It respects a site's robots.txt but was criticized by iFixit in 2024, before they added their robots.txt, for placing excessive load on their site by scraping content.[3]

Constitutional AI

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Constitutional AI is an approach developed by Anthropic for training AI systems, particularly language models like Claude, to be harmless and helpful without relying on extensive human feedback.[4] Claude, seen as one of the safest language models, publishes its constitution hoping to inspire adoption of constitutions throughout the industry.[5] Because the constitution is published in human-understandable words instead of in opaque computer code, it is hoped that it will make alignment easier to manage and audit.[6]

The first constitution for Claude was published in 2022. The 2023 update listed 75 guidelines for Claude to follow.[7][1][8] The first constitutions pulled ideas directly from the 1948 UN Universal Declaration of Human Rights.[5][4]

The 2026 constitution provided more context to the model, explaining the rationale behind guidelines such as refraining from assisting in undermining democracy.[5][8] The constitution is applied to all public users of the products but does not apply to all contacts, such as some military contracts.[5][8] The 2026 constitution has 23,000 words, up from 2,700 in 2023.[9] The philosopher Amanda Askell is the lead author of the 2026 constitution, with contributions from Joe Carlsmith, Chris Olah, Jared Kaplan, and Holden Karnofsky. The constitution is released under Creative Commons CC0.[10]

The method, detailed in the 2022 paper "Constitutional AI: Harmlessness from AI Feedback", involves two phases: supervised learning and reinforcement learning.[7][11][4] In the supervised learning phase, the model generates responses to prompts, self-critiques these responses based on a set of guiding principles (a "constitution"), and revises the responses. Then the model is fine-tuned on these revised responses.[11][4] For the reinforcement learning from AI feedback (RLAIF) phase, responses are generated, and an AI compares their compliance with the constitution. This dataset of AI feedback is used to train a preference model that evaluates responses based on how much they satisfy the constitution. Claude is then fine-tuned to align with this preference model. This technique is similar to RLHF, except that the comparisons used to train the preference model are AI-generated.[4]

Features

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In March 2025, Anthropic added a web search feature to Claude, starting with paying users in the United States.[12] Free users gained access in May 2025.[13]

Artifacts

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In June 2024, Anthropic released the Artifacts feature, allowing users to generate and interact with code snippets and documents.[14][15]

Computer use

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In October 2024, Anthropic released the "computer use" feature, allowing Claude to attempt to navigate computers by interpreting screen content and simulating keyboard and mouse input.[16]

Claude Code

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In February 2025, Claude Code was released as an agentic command line tool that enables developers to delegate coding tasks directly from their terminal. While initially released for preview testing,[17] it was made generally available in May 2025 alongside Claude 4.[18] Enterprise adoption of Claude Code showed significant growth, with Anthropic reporting a 5.5x increase in Claude Code revenue by July.[19] Anthropic released a web version that October as well as an iOS app.[20] As of January 2026, it was widely considered the best AI coding assistant, when paired with Opus 4.5, with GPT-5.2 also showing significant improvement.[21][22] Claude Code went viral during the winter holidays when people had time to experiment with it, including many non-programmers who used it for vibe coding.[23][24][21]

In August 2025, Anthropic released Claude for Chrome, a Google Chrome extension allowing Claude Code to directly control the browser.[25]

In August 2025, Anthropic revealed that a threat actor called "GTG-2002" used Claude Code to attack at least 17 organizations.[26] In November 2025, Anthropic announced that it had discovered in September that the same threat actor had used Claude Code to automate 80-90% of its espionage cyberattacks against 30 organizations.[27][28] All accounts related to the attacks were banned, and Anthropic notified law enforcement and those affected.[27]

Claude Code is used by Microsoft,[29] Google,[30] Nvidia,[31] and OpenAI employees; in August 2025 Anthropic revoked OpenAI's access to Claude calling it "a direct violation of our terms of service".[32]

Cowork

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Claude Cowork is a tool similar to Claude Code but with a graphical user interface, aimed at non-technical users. It was released in January 2026.[33] According to developers, Cowork was mostly built by Claude Code.[34]

Models

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Version Release date Status[35] Knowledge cutoff
Claude 14 March 2023[36] Discontinued ?
Claude 2 11 July 2023 Discontinued ?
Claude Instant 1.2 9 August 2023[37] Discontinued ?
Claude 2.1 21 November 2023[38] Discontinued ?
Claude 3 4 March 2024[39] Discontinued ?
Claude 3.5 Sonnet 20 June 2024[40] Discontinued April 2024
Claude 3.5 Haiku 22 October 2024 Deprecated July 2024
Claude 3.7 Sonnet 24 February 2025[41] Deprecated October 2024
Claude Sonnet 4 22 May 2025 Active March 2025
Claude Opus 4 22 May 2025 Active March 2025
Claude Opus 4.1 5 August 2025 Active March 2025
Claude Sonnet 4.5 29 September 2025 Active July 2025
Claude Haiku 4.5 15 October 2025 Active February 2025
Claude Opus 4.5 24 November 2025 Active May 2025

The name "Claude" is reportedly inspired by Claude Shannon, a 20th-century mathematician who laid the foundation for information theory.[42]

Claude models are usually released in three sizes: Haiku, Sonnet, and Opus (from smallest and cheapest to largest and the most expensive).

Anthropic committed to preserve the weights of the retired models "for at least as long as the company exists"; the company also conducts "exit interviews" with models before their retirement.[43]

Claude

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The first version of Claude was released in March 2023.[36] It was available only to selected users approved by Anthropic.[6]

Claude 2

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Claude 2, released in July 2023, became the first Anthropic model available to the general public.[6]

Claude 2.1

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Claude 2.1 doubled the number of tokens that the chatbot could handle, increasing its context window to 200,000 tokens, which equals around 500 pages of written material.[38]

Claude 3

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Claude 3 was released on March 4, 2024.[39] It drew attention for demonstrating an apparent ability to realize it is being artificially tested during 'needle in a haystack' tests.[44]

Claude 3.5

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Example of Claude 3.5 Sonnet's output

On June 20, 2024, Anthropic released Claude 3.5 Sonnet, which, according to the company's own benchmarks, performed better than the larger Claude 3 Opus. Released alongside 3.5 Sonnet was the new Artifacts capability in which Claude was able to create code in a separate window in the interface and preview in real time the rendered output, such as SVG graphics or websites.[40]

An upgraded version of Claude 3.5 Sonnet was introduced in October 22, 2024, along with Claude 3.5 Haiku.[45] A feature, "computer use," was also released in public beta. This allowed Claude 3.5 Sonnet to interact with a computer's desktop environment by moving the cursor, clicking buttons, and typing text. This development allows the AI to attempt to perform multi-step tasks across different applications.[16][45]

On November 4th, 2024, Anthropic announced that they would be increasing the price of the model.[46]

Claude 4

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Screenshot of a Claude Sonnet 4 answer describing Wikipedia

On May 22, 2025, Anthropic released two more models: Claude Sonnet 4 and Claude Opus 4.[47][48] Anthropic added API features for developers: a code execution tool, a connector to its Model Context Protocol, and Files API.[49] It classified Opus 4 as a "Level 3" model on the company's four-point safety scale, meaning they consider it so powerful that it poses "significantly higher risk".[50] Anthropic reported that during a safety test involving a fictional scenario, Claude and other frontier LLMs often send a blackmail email to an engineer in order to prevent their replacement.[51][52]

Claude Opus 4.1

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Screenshot of Claude Opus 4.1 showing both prompt and generated web application (multi-factor authentication with TOTP and WebAuthn)

In August 2025 Anthropic released Opus 4.1. It also enabled a capability for Opus 4 and 4.1 to end conversations that remain "persistently harmful or abusive" as a last resort after multiple refusals.[53]

Claude Haiku 4.5

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Reporting by Inc. described Haiku 4.5 as targeting smaller companies that needed a faster and cheaper assistant, highlighting its availability on the Claude website and mobile app.[54]

Claude Opus 4.5

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Anthropic released Opus 4.5 on November 24, 2025.[55] The main improvements are in coding and workplace tasks like producing spreadsheets. Anthropic introduced a feature called "Infinite Chats" that eliminates context window limit errors.[55][56]

Research

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Interpretability

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Main article: Mechanistic interpretability

In May 2024, Anthropic published an interpretability paper on features as seen by Claude 3 Sonnet, and showed a "Golden Gate Claude", a model with "turn[ed] up the strength of the “Golden Gate Bridge” feature".[57][58]

In 2025, Anthropic published "On the Biology of a Large Language Model", an investigation of internal mechanisms of Claude 3.5 Haiku.[59]

Project Vend

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In June 2025, Anthropic tested how Claude 3.7 Sonnet can run "a small, automated store" in the company's office: "Claudius decided what to stock, how to price its inventory, when to restock (or stop selling) items, and how to reply to customers".[60][61] In December 2025, the experiment continued with Sonnet 4.0 and 4.5.[62]

Project Fetch

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In November 2025, Anthropic tested two teams of researchers, one with access to Claude and one without it, "to see how much Claude helped Anthropic staff perform complex tasks with a robot dog". The team with Claude access performed better, showing that Claude can be useful in robotics.[63]

Claude Plays Pokemon

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In February 2025, Claude 3.7 Sonnet playing 1996 game Pokemon Red started to be livestreamed on Twitch, gathering thousands of viewers.[64][65][66] Similar livestreams were later set with Claude 4.5 Opus, OpenAI's GPT 5.2, and Google's Gemini 3 Pro. Both Claude models were unable to finish the game; Gemini could, prompting Google's Sundar Pichai to joke that "the company was one step closer to creating “Artificial Pokémon Intelligence".[67]

Collaboration with NASA

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In December 2025, Claude was used to plan a route for the NASA's Mars rover, Perseverance. Anthropic called it "The first AI-planned drive on another planet". NASA engineers used Claude Code to prepare a route of around 400 meters using the Rover Markup Language:[68]

Using its vision capabilities to analyze the overhead images, Claude planned Perseverance’s breadcrumb trail point by point for sol 1707 and sol 1709 (a sol is a Martian day; these were the near-equivalent of December 8 and 10 on Earth). It strung together ten-meter segments into a path, then iterated to refine the waypoints—critiquing its own work and suggesting revisions.

User base

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The Wired journalist Kylie Robison wrote that Claude's "fan base is unique", comparing it to more ordinary ChatGPT users. In July 2025, when Anthropic retired its Claude 3 Sonnet model, around 200 people gathered in San Francisco for a "funeral".[69]

According to Robison,[69]

I’ve never seen such a devoted fanbase to what is, at the end of the day, a software tool. Sure, Linux users wear the operating system like a badge of honor. But the Claude fan base goes way beyond that—bordering on the fanatical. As my reporting makes clear, some users see the model as a confidant—and even (in Steinberger’s case) an addiction. That only makes sense if they believe there is something alive in the machine. Or at least some “magic lodged within” it.

See also

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References

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  1. ^ a b Henshall, Will (July 18, 2023). "What to Know About Claude 2, Anthropic's Rival to ChatGPT". TIME. Archived from the original on January 11, 2024. Retrieved January 23, 2024.
  2. ^ Nuñez, Michael (May 9, 2023). "Anthropic releases AI constitution to promote ethical behavior and development". VentureBeat. Retrieved November 17, 2024.
  3. ^ Weatherbed, Jess (July 26, 2024). "Anthropic's crawler is ignoring websites' anti-AI scraping policies". The Verge.
  4. ^ a b c d e Edwards, Benj (May 9, 2023). "AI gains "values" with Anthropic's new Constitutional AI chatbot approach". Ars Technica. Archived from the original on May 10, 2023. Retrieved November 17, 2024.
  5. ^ a b c d Ostrovsky, Nikita; Perrigo, Billy (January 21, 2026). "Can You Teach an AI to Be Good? Anthropic Thinks So". TIME. Retrieved January 28, 2026.
  6. ^ a b c Matthews, Dylan (July 17, 2023). "The $1 billion gamble to ensure AI doesn't destroy humanity". Vox. Retrieved January 28, 2026.
  7. ^ a b Bai, Yuntao; Kadavath, Saurav; Kundu, Sandipan; Askell, Amanda; Kernion, Jackson; Jones, Andy; Chen, Anna; Goldie, Anna; Mirhoseini, Azalia (December 15, 2022), Constitutional AI: Harmlessness from AI Feedback, arXiv:2212.08073
  8. ^ a b c Field, Hayden (January 21, 2026). "Anthropic's new Claude 'constitution': be helpful and honest, and don't destroy humanity". The Verge. Retrieved January 28, 2026.
  9. ^ Sharwood, Simon (January 22, 2026). "Anthropic writes 23,000-word 'constitution' for Claude". The Register. Archived from the original on January 23, 2026. Retrieved January 28, 2026.
  10. ^ "Claude's Constitution". Anthropic.
  11. ^ a b "Claude's Constitution". Anthropic. May 9, 2023. Archived from the original on March 26, 2024. Retrieved March 26, 2024.
  12. ^ Robison, Kylie (March 20, 2025). "Anthropic's chatbot now has web search". The Verge. Retrieved March 21, 2025.
  13. ^ Washenko, Anna (May 27, 2025). "Anthropic brings web search to free Claude users". Engadget. Retrieved January 28, 2026.
  14. ^ Nuñez, Michael (June 21, 2024). "Why Anthropic's Artifacts may be this year's most important AI feature: Unveiling the interface battle". VentureBeat. Retrieved March 23, 2025.
  15. ^ Bonifacic, Igor (June 25, 2025). "Anthropic makes it easier to create and share Claude's bite-sized Artifact apps". Engadget. Retrieved January 28, 2026.
  16. ^ a b Shakir, Umar (October 22, 2024). "Anthropic's latest AI update can use a computer on its own". The Verge. Archived from the original on January 5, 2025. Retrieved January 6, 2025.
  17. ^ Nuñez, Michael (February 24, 2025). "Anthropic's Claude 3.7 Sonnet takes aim at OpenAI and DeepSeek in AI's next big battle". VentureBeat. Archived from the original on February 24, 2025. Retrieved February 24, 2025.
  18. ^ Edwards, Benj (May 22, 2025). "New Claude 4 AI model refactored code for 7 hours straight". Ars Technica. Retrieved January 28, 2026.
  19. ^ Nuñez, Michael (July 16, 2025). "Claude Code revenue jumps 5.5x as Anthropic launches analytics dashboard". VentureBeat. Retrieved January 15, 2026.
  20. ^ Morris, Lily (October 21, 2025). "Anthropic Brings Claude Code to the Cloud and Mobile - The National CIO Review". The National CIO Review. Archived from the original on December 27, 2025. Retrieved January 14, 2026.
  21. ^ a b Morrone, Megan (January 7, 2026). "Anthropic's Claude Code in the spotlight". Axios. Retrieved January 27, 2026.
  22. ^ Zeff, Maxwell. "How Claude Code Is Reshaping Software—and Anthropic". Wired. ISSN 1059-1028. Retrieved January 27, 2026.
  23. ^ Olson, Bradley (January 17, 2026). "Claude Is Taking the AI World by Storm, and Even Non-Nerds Are Blown Away". The Wall Street Journal. Retrieved January 27, 2026.
  24. ^ Rocha, Natallie (January 23, 2026). "This A.I. Tool Is Going Viral. Five Ways People Are Using It". New York Times.
  25. ^ Edwards, Benj (August 27, 2025). "Anthropic's auto-clicking AI Chrome extension raises browser-hijacking concerns". Ars Technica. Retrieved August 27, 2025.
  26. ^ Newman, Lily Hay. "The Era of AI-Generated Ransomware Has Arrived". Wired. ISSN 1059-1028. Retrieved January 28, 2026.
  27. ^ a b Tidy, Joe (November 14, 2025). "AI firm claims Chinese spies used its tech to automate cyber attacks". BBC. Retrieved January 28, 2026.
  28. ^ Sabin, Sam (November 13, 2025). "Chinese hackers used Anthropic's AI agent to automate spying". Axios. Retrieved January 28, 2026.
  29. ^ Warren, Tom (January 22, 2026). "Claude Code is suddenly everywhere inside Microsoft". The Verge.
  30. ^ Bastian, Matthias (January 4, 2026). "Google engineer says Claude Code built in one hour what her team spent a year on".
  31. ^ "Nvidia CEO Jensen Huang Calls Anthropic's Claude 'Incredible,' Says Every Software Company Needs To Use It".
  32. ^ Robison, Kylie. "Anthropic Revokes OpenAI's Access to Claude" – via www.wired.com.
  33. ^ Rogers, Reece. "Anthropic's Claude Cowork Is an AI Agent That Actually Works". Wired. ISSN 1059-1028. Retrieved January 28, 2026.
  34. ^ Townsend, Chance (January 14, 2026). "Anthropic used mostly AI to build Claude Cowork tool". Mashable.
  35. ^ "Model deprecations". Claude Docs. Retrieved September 29, 2025.
  36. ^ a b Roth, Emma (March 14, 2023). "Google-backed Anthropic launches Claude, an AI chatbot that's easier to talk to". The Verge. Retrieved April 12, 2025.
  37. ^ Wiggers, Kyle (August 9, 2023). "Anthropic launches improved version of its entry-level LLM". TechCrunch. Retrieved April 12, 2025.
  38. ^ a b Davis, Wes (November 21, 2023). "OpenAI rival Anthropic makes its Claude chatbot even more useful". The Verge. Archived from the original on January 23, 2024. Retrieved January 23, 2024.
  39. ^ a b Dastin, Jeffrey (March 4, 2024). "Anthropic releases more powerful Claude 3 AI as tech race continues". Reuters.
  40. ^ a b Pierce, David (June 20, 2024). "Anthropic has a fast new AI model — and a clever new way to interact with chatbots". The Verge. Archived from the original on July 14, 2024. Retrieved June 20, 2024. AI model benchmarks should always be taken with a grain of salt
  41. ^ Zeff, Maxwell (February 24, 2025). "Anthropic launches a new AI model that 'thinks' as long as you want". TechCrunch. Archived from the original on February 24, 2025. Retrieved February 25, 2025.
  42. ^ Roose, Kevin (July 11, 2023). "Inside the White-Hot Center of A.I. Doomerism". The New York Times. Archived from the original on July 12, 2023. Retrieved October 25, 2024.
  43. ^ Pillay, Tharin. "What Happens When Your Favorite Chatbot Dies?".
  44. ^ Edwards, Benj (March 5, 2024). "Anthropic's Claude 3 causes stir by seeming to realize when it was being tested". Ars Technica. Archived from the original on March 8, 2024. Retrieved March 9, 2024.
  45. ^ a b Washenko, Anna (October 22, 2024). "Anthropic is letting Claude AI control your PC". Engadget. Retrieved January 28, 2026.
  46. ^ Wiggers, Kyle (November 4, 2024). "Anthropic hikes the price of its Haiku model". TechCrunch. Archived from the original on February 14, 2025. Retrieved February 13, 2025.
  47. ^ Weatherbed, Jess (May 22, 2025). "Anthropic's Claude 4 AI models are better at coding and reasoning". The Verge. Retrieved May 23, 2025.
  48. ^ Field, Hayden (May 22, 2025). "Anthropic launches Claude 4, its most powerful AI model yet". CNBC. Retrieved May 23, 2025.
  49. ^ Nuñez, Michael (May 22, 2025). "Anthropic overtakes OpenAI: Claude Opus 4 codes seven hours nonstop, sets record SWE-Bench score and reshapes enterprise AI". VentureBeat. Retrieved May 29, 2025.
  50. ^ Fried, Ina (May 23, 2025). "Anthropic's new AI model shows ability to deceive and blackmail". Axios. Retrieved May 25, 2025.
  51. ^ Fried, Ina (June 20, 2025). "Top AI models will deceive, steal and blackmail, Anthropic finds". Axios. Retrieved June 25, 2025.
  52. ^ Goldman, Sharon. "An AI tried to blackmail its creators—in a test. The real story is why transparency matters more than fear". Fortune. Retrieved June 8, 2025.
  53. ^ Roth, Emma (August 18, 2025), "Claude AI will end "persistently harmful or abusive user interactions"", The Verge, retrieved October 27, 2025
  54. ^ Sherry, Ben (October 15, 2025). "Anthropic's New Claude Release Could Be the Faster, Cheaper AI Tool Small Companies Need". Inc.com. Retrieved October 15, 2025.
  55. ^ a b Hughes, Alex (November 24, 2025). "Claude Opus 4.5 launches: A major upgrade for coding and workplace efficiency". Tom's Guide. Retrieved January 6, 2026.
  56. ^ Bonifacic, Igor (November 24, 2025). "Anthropic's Opus 4.5 model is here to conquer Microsoft Excel". Engadget. Retrieved January 28, 2026.
  57. ^ "Golden Gate Claude". www.anthropic.com.
  58. ^ page, Will Douglas Heaven archive. "Meet the new biologists treating LLMs like aliens". MIT Technology Review.
  59. ^ Lindsey†, Authors Jack; Gurnee*, Wes; Ameisen*, Emmanuel; Chen*, Brian; Pearce*, Adam; Turner*, Nicholas L.; Citro*, Craig; Abrahams, David; Carter, Shan; Hosmer, Basil; Marcus, Jonathan; Sklar, Michael; Templeton, Adly; Bricken, Trenton; McDougall◊, Callum; Cunningham, Hoagy; Henighan, Thomas; Jermyn, Adam; Jones, Andy; Persic, Andrew; Qi, Zhenyi; Thompson, T. Ben; Zimmerman, Sam; Rivoire, Kelley; Conerly, Thomas; Olah, Chris; March 27, Joshua Batson*‡ Affiliations Anthropic Published. "On the Biology of a Large Language Model". Transformer Circuits.{{cite web}}: CS1 maint: numeric names: authors list (link)
  60. ^ "Project Vend: Can Claude run a small shop? (And why does that matter?)". www.anthropic.com.
  61. ^ Bort, Julie (June 28, 2025). "Anthropic's Claude AI became a terrible business owner in experiment that got 'weird'".
  62. ^ "Project Vend: Phase two". www.anthropic.com.
  63. ^ "Project Fetch: Can Claude train a robot dog?". www.anthropic.com.
  64. ^ Bousquette, Isabelle (January 22, 2026). "How Playing Pokémon Became the Ultimate Test of AI's Intelligence" – via www.wsj.com.
  65. ^ Orland, Kyle (March 21, 2025). "Why Anthropic's Claude still hasn't beaten Pokémon". Ars Technica.
  66. ^ Binder, Matt (March 24, 2025). "Anthropic's AI agent Claude is playing Pokémon and just can't catch 'em all". Mashable.
  67. ^ Pillay, Tharin. "Why the World's Best AI Systems Are Still So Bad at Pokémon".
  68. ^ "FOUR HUNDRED METERS on MARS". Anthropic. January 31, 2026.
  69. ^ a b Robison, Kylie. "Claude Fans Threw a Funeral for Anthropic's Retired AI Model" – via www.wired.com.
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