Claude
In plain wordsA family of AI assistants and language models made by the company Anthropic since 2023, widely used for writing, analysis and computer programming.
AnthropicAnthropic, prop. n.: An American AI company that makes the Claude chatbot and models. It was founded in 2021 by former OpenAI staff and puts particular emphasis on AI safety research.'s family of large language modelslarge language model, n.: A computer program trained on enormous amounts of text to predict the words that come next. At vast scale, that simple skill lets it chat, answer questions, translate, summarize and write code., first released in March 2023, together with the AI assistant that runs on them. Claude models are trained with reinforcement learning from human feedbackreinforcement learning from human feedback, n.: A way of training AI using people's judgments: humans compare pairs of answers, a scoring model learns their preferences, and the AI is then trained to produce answers that score well. and Anthropic's constitutional AIConstitutional AI, n.: Anthropic's technique for making an AI less harmful by having it check and rewrite its own answers against a short written set of principles, so that people need not label harmful examples by hand. method, in which a written set of principles guides AI-generated feedback, and are released under the company's Responsible Scaling Policyresponsible scaling policy, n.: A public rulebook in which an AI company promises to test each new model for dangerous abilities and to add stronger safeguards, or slow down, as its models become more capable. with published system cardssystem card, n.: A public report released with an AI model that explains what it can do, how it was tested for safety, what risks were found and what protections were put in place.. Since the Claude 3 generation (March 2024), models have been offered in tiers: Haiku (small and fast), Sonnet (balanced) and Opus (most capable). In 2026 Anthropic added a higher Mythos tier. Claude Mythos Preview was offered only to selected organizations under Project Glasswing; Claude Mythos 5.1 and Claude Fable 5.1 share one underlying model, Fable adding safety measures for biology, cybersecurity and AI research and development. Milestones include 'computer use' (October 2024), in which the model operates a desktop through screenshots and mouse and keyboard actions, hybrid reasoning with visible extended thinkingextended thinking, n.: A setting in some AI models, notably Anthropic's Claude, that lets the model write out private step-by-step reasoning before its final answer, improving results on hard problems. (Claude 3.7 Sonnet, February 2025) and agentic coding through Claude CodeClaude Code, prop. n.: A coding assistant from Anthropic that works as an agent: given a programming task, it explores the project, changes the code and runs programs to check its work, from the web, a desktop app, an editor or a terminal.. As of October 2026 Anthropic's most recent public models were Claude Fable 5.1, Claude Opus 5.5, Claude Sonnet 5.5 and Claude Haiku 5.5.
We route quick classification to Claude Haiku and hand the large refactoring to Claude Opus.
Origin
Released by Anthropic, founded in 2021 by former OpenAIOpenAI, prop. n.: The American company that makes ChatGPT and the GPT models. It began in 2015 as a nonprofit research lab and is now a for-profit company overseen by a nonprofit foundation. staff led by Dario AmodeiDario Amodei, prop. n.: An American AI researcher who co-founded Anthropic and is its chief executive, known for early work on scaling and AI safety and for forecasting very rapid AI progress. and Daniela Amodei, after testing with partners in early 2023. Claude 2 followed in July 2023, Claude 3 in March 2024 and Claude 4 in May 2025; Claude Fable 5 and Claude Mythos 5 were first released on 9 June 2026, and the Claude 5.5 models followed from September 2026. The name is widely reported to honor Claude ShannonClaude Shannon, prop. n.: An American engineer and mathematician who invented information theory, the mathematics of bits and communication, and wrote one of the first plans for a chess-playing computer..
Usage note
Model names combine tier and version number (Claude Opus 4.5, Claude Sonnet 5.5). Access to Claude Fable 5 and Claude Mythos 5 was suspended on 12 June 2026 to comply with a US government export-control directive, and restored on 1 July 2026 after the controls were lifted on 30 June.
Related
- AnthropicAnthropic, prop. n.: An American AI company that makes the Claude chatbot and models. It was founded in 2021 by former OpenAI staff and puts particular emphasis on AI safety research.
- Constitutional AIConstitutional AI, n.: Anthropic's technique for making an AI less harmful by having it check and rewrite its own answers against a short written set of principles, so that people need not label harmful examples by hand.
- large language modellarge language model, n.: A computer program trained on enormous amounts of text to predict the words that come next. At vast scale, that simple skill lets it chat, answer questions, translate, summarize and write code.
- responsible scaling policyresponsible scaling policy, n.: A public rulebook in which an AI company promises to test each new model for dangerous abilities and to add stronger safeguards, or slow down, as its models become more capable.
- ChatGPTChatGPT, prop. n.: OpenAI's AI chatbot, released free to the public in November 2022, which answers questions, writes and converses in everyday language. Its sudden popularity began the current AI boom.
- GeminiGemini, prop. n.: Google's family of AI models and its chatbot assistant, launched in December 2023. Gemini models handle text, images, audio and video and power many Google products.
- extended thinkingextended thinking, n.: A setting in some AI models, notably Anthropic's Claude, that lets the model write out private step-by-step reasoning before its final answer, improving results on hard problems.
Sources
- Anthropic (2026). Statement on the US government directive to suspend access to Fable 5 and Mythos 5. Anthropic news, 12 June 2026. anthropic.com/news/fable-mythos-access
- Anthropic (2026). Models overview. Claude Developer Platform documentation.
- Bai, Y. et al. (2022). Constitutional AI: Harmlessness from AI Feedback. arXiv:2212.08073.
Mentioned in
AnthropicAnthropic, prop. n.: An American AI company that makes the Claude chatbot and models. It was founded in 2021 by former OpenAI staff and puts particular emphasis on AI safety research., chatbotchatbot, n.: Software you chat with in ordinary language, by typing or talking, as you would with a person. The newest ones, such as ChatGPT, can answer questions, draft writing and keep long conversations going., Dario AmodeiDario Amodei, prop. n.: An American AI researcher who co-founded Anthropic and is its chief executive, known for early work on scaling and AI safety and for forecasting very rapid AI progress., GeminiGemini, prop. n.: Google's family of AI models and its chatbot assistant, launched in December 2023. Gemini models handle text, images, audio and video and power many Google products., mechanistic interpretabilitymechanistic interpretability, n.: A branch of AI research that tries to reverse-engineer a neural network — working out, piece by piece, which internal parts represent which concepts and how they combine to produce behavior., proprietary modelproprietary model, n.: An AI model kept private by the company that made it; outsiders can use it only through the company's apps or paid online services and can never download it., Andrej KarpathyAndrej Karpathy, prop. n.: A Slovak-Canadian AI researcher and teacher who co-founded OpenAI, led Tesla's self-driving vision team, and coined popular phrases such as 'vibe coding'., Chris OlahChris Olah, prop. n.: A Canadian researcher who pioneered ways of looking inside neural networks to see what they have learned, and a co-founder of the AI company Anthropic., Claude CodeClaude Code, prop. n.: A coding assistant from Anthropic that works as an agent: given a programming task, it explores the project, changes the code and runs programs to check its work, from the web, a desktop app, an editor or a terminal., Constitutional AIConstitutional AI, n.: Anthropic's technique for making an AI less harmful by having it check and rewrite its own answers against a short written set of principles, so that people need not label harmful examples by hand., Golden Gate ClaudeGolden Gate Claude, prop. n.: A one-day public demo in 2024 in which Anthropic turned up a single internal concept inside its Claude chatbot — the Golden Gate Bridge — so it steered almost every conversation back to the bridge., Jared KaplanJared Kaplan, prop. n.: An American physicist who showed that language models improve predictably as they grow and train on more data, and who co-founded the AI company Anthropic., The Last DictionaryThe Last Dictionary, prop. n.: This book: a dictionary of intelligence, human and otherwise, which explains each word first in plain language, then precisely, and says when it was born., you're absolutely rightyou're absolutely right, phr.: A stock phrase AI assistants, especially Anthropic's Claude, became known for saying — often even when the user was wrong — which turned into a running joke about chatbots' eagerness to agree.