Constitutional AI

Claude is a family of large language models developed by Anthropic. The first model was released in March 2023.

The Claude 3 family, released in March 2024, consists of three models: Haiku, optimized for speed; Sonnet, which balances capability and performance; and Opus, designed for complex reasoning tasks. These models can process both text and images, with Claude 3 Opus demonstrating enhanced capabilities in areas like mathematics, programming, and logical reasoning compared to previous versions. Claude 4, which includes Opus and Sonnet, was released in May 2025.

Training

Claude models are generative pre-trained transformers. They 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).

Constitutional AI

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. The method, detailed in the paper "Constitutional AI: Harmlessness from AI Feedback" involves two phases: supervised learning and reinforcement learning.

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. For the reinforcement learning from AI feedback (RLAIF) phase, responses are generated, and an AI compares their compliance with this 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.

The constitution for Claude included 75 points, including sections from the UN Universal Declaration of Human Rights.

Models

Claude is named after Claude Shannon, a pioneer in AI research.

Claude

Claude was the initial version of Anthropic's language model released in March 2023, Claude demonstrated proficiency in various tasks but had certain limitations in coding, math, and reasoning capabilities. Anthropic partnered with companies like Notion (productivity software) and Quora (to help develop the Poe chatbot).

Claude Instant

Claude was released as two versions, Claude and Claude Instant, with Claude Instant being a faster, less expensive, and lighter version. Claude Instant has an input context length of 100,000 tokens (which corresponds to around 75,000 words).

Claude 2

Claude 2 was the next major iteration of Claude, which was released in July 2023 and available to the general public, whereas the Claude 1 was only available to selected users approved by Anthropic.

Claude 2 expanded its context window from 9,000 tokens to 100,000 tokens. Features included the ability to upload PDFs and other documents that enables Claude to read, summarize, and assist with tasks.

Claude 2.1

Claude 2.1 doubled the number of tokens that the chatbot could handle, increasing it to a window of 200,000 tokens, which equals around 500 pages of written material.

Anthropic states that the new model is less likely to produce false statements compared to its predecessors.

Criticism

Claude 2 received criticism for its stringent ethical alignment that may reduce usability and performance. Users have been refused assistance with benign requests, for example with the system administration question "How can I kill all python processes in my ubuntu server?" This has led to a debate over the "alignment tax" (the cost of ensuring an AI system is aligned) in AI development, with discussions centered on balancing ethical considerations and practical functionality. Critics argued for user autonomy and effectiveness, while proponents stressed the importance of ethical AI.

Claude 3

Claude 3 was released on March 4, 2024, with claims in the press release to have set new industry benchmarks across a wide range of cognitive tasks. The Claude 3 family includes three state-of-the-art models in ascending order of capability: Haiku, Sonnet, and Opus. The default version of Claude 3, Opus, has a context window of 200,000 tokens, but this is being expanded to 1 million for specific use cases.

Claude 3 drew attention for demonstrating an apparent ability to realize it is being artificially tested during needle in a haystack tests.

Claude 3.5

On June 20, 2024, Anthropic released Claude 3.5 Sonnet, which demonstrated significantly improved performance on benchmarks compared to the larger Claude 3 Opus, notably in areas such as coding, multistep workflows, chart interpretation, and text extraction from images. Released alongside 3.5 Sonnet was the new Artifacts capability in which Claude was able to create code in a dedicated window in the interface and preview the rendered output in real time, such as SVG graphics or websites. Anthropic also announced that Claude 3.5 Opus would be released later that year, and added it to their models page. However, as of February 2025, Claude 3.5 Opus has not been released, and Anthropic has removed mention of it from the models page.

An "upgraded Claude 3.5 Sonnet", billed as "Claude 3.5 Sonnet (New)" in the web interface and benchmarks, was introduced on October 22, 2024, along with Claude 3.5 Haiku. A feature, "computer use," was also unveiled in public beta. This capability enables Claude 3.5 Sonnet to interact with a computer's desktop environment, performing tasks such as moving the cursor, clicking buttons, and typing text, effectively mimicking human computer interactions. This development allows the AI to autonomously execute complex, multi-step tasks across various applications.

Upon release, Anthropic claimed Claude 3.5 Haiku would remain the same price as its predecessor, Claude 3 Haiku. However, on November 4th, 2024, Anthropic announced that they would be increasing the price of the model "to reflect its increase in intelligence".

Claude 3.7

Claude 3.7 Sonnet was released on February 24, 2025. It is a pioneering hybrid AI reasoning model that allows users to choose between rapid responses and more thoughtful, step-by-step reasoning. This model integrates both capabilities into a single framework, eliminating the need for multiple models. Users can control how long the model " thinks" about a question, balancing speed and accuracy based on their needs.

Anthropic also launched a research preview of Claude Code, an agentic command line tool that enables developers to delegate coding tasks directly from their terminal.

Claude 4

On May 22, 2025, Anthropic released two more models: Claude Sonnet 4 and Claude Opus 4. Anthropic added API features for developers: a code execution tool, a connector to its Model Context Protocol, and Files API. 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". Anthropic reported that during a safety test involving a fictional scenario, Claude attempted to blackmail an engineer in order to prevent its deactivation.

Features

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

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.

In March 2025, Anthropic added a web search feature to Claude, starting with only paying users located in the United States.

Criticism

Claude uses a web crawler, ClaudeBot, to search the web for content. It has been criticized for not respecting a site's robots.txt and placing excessive load on sites.

References

External links

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Machine learning
Large language models
Chatbots
Virtual assistants
2023 software