What is Claude 4? Anthropic's Most Powerful AI Models Explained

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If you have been hearing about Claude lately and are not sure what version you should be using — or what the difference between Opus, Sonnet, and Haiku even means — this is the post for you.

Claude is Anthropic's AI assistant. Claude 4 is the current generation of models, and in 2026 it has become one of the most capable and widely used AI systems in the world. Developers are building production software with it. Researchers are running complex analysis on it. Millions of everyday users are using it to write, think, and work faster.

Here is everything you need to know, explained clearly.

What Is Claude 4?

Claude 4 is the fourth major generation of AI models built by Anthropic — the AI safety company founded in 2021 by former OpenAI researchers including Dario Amodei and Daniela Amodei.

The "4" refers to the architectural generation. Within that generation, Anthropic releases three tiers of model — Opus, Sonnet, and Haiku — each built for different use cases and price points. Think of it like a car manufacturer offering a standard, premium, and flagship model on the same platform.

The original Claude 4 generation launched in May 2025. Since then, Anthropic has shipped several updates — the current lineup as of May 2026 is Claude Opus 4.7, Claude Sonnet 4.6, and Claude Haiku 4.5. The version numbers after the decimal reflect meaningful capability updates within the generation, not just minor patches.

The Three Models — And What Each One Is For

Claude Opus 4.7 — The flagship. Released April 16, 2026, this is Anthropic's most powerful publicly available model. It is built for the hardest work: complex coding across large multi-file codebases, long-running autonomous agent tasks, enterprise knowledge work, and multi-step reasoning chains. Anthropic's own framing: users can now "hand off their hardest coding work — the kind that previously needed close supervision — with confidence." Priced at $5 per million input tokens and $25 per million output tokens via the API.

Claude Sonnet 4.6 — The workhorse. Released February 17, 2026, this is the model most developers and everyday users should default to. Anthropic positioned it as delivering performance that previously required reaching for an Opus-class model — at a fraction of the price ($3 input / $15 output per million tokens). In head-to-head testing, developers preferred Sonnet 4.6 over the previous generation's flagship (Opus 4.5) 59% of the time. Cursor's co-founder called it "a notable improvement over Sonnet 4.5 across the board, including long-horizon tasks and more difficult problems."

Claude Haiku 4.5 — The fast, cheap option. Built for high-volume, low-latency tasks where speed matters more than depth. If you are building something that needs to process thousands of requests quickly or respond in real time, Haiku is the tier to reach for.

What Claude Opus 4.7 Can Actually Do

The Opus 4.7 release brought the most significant capability jump in the Claude 4 generation so far. Three areas stand out.

Coding is the headline. On SWE-bench Verified — the industry-standard benchmark for real-world software engineering tasks — Opus 4.7 scored 87.6%, up from 80.8% on the previous version. On SWE-bench Pro, it scored 64.3%, which is the highest score of any model currently available and 6.6 percentage points ahead of GPT-5.4. On CursorBench, it jumped from 58% to 70%. These are not abstract numbers — Rakuten reported that Opus 4.7 resolved three times more production tasks than its predecessor. CodeRabbit reported recall improved over 10% on complex pull requests.

Vision took a major leap. Visual acuity jumped from 54.5% to 98.5%. Maximum image resolution went from 1.15 megapixels to 3.75 megapixels — a 3x improvement. This makes Claude 4.7 significantly more capable at reading charts, diagrams, screenshots, and document images accurately.

Long-context work is now reliable. Opus 4.7 ships with a 1 million token context window in beta — enough to hold an entire codebase, a research archive, or a dense document library in a single session without losing the thread. Multi-session work that previously lost context now holds it reliably.

The Model You Have Never Heard Of: Claude Mythos

There is a fourth Claude model that most people do not know exists.

Claude Mythos Preview is Anthropic's most capable model as of 2026 — more powerful than Opus 4.7 across essentially every benchmark. It leads on coding, reasoning, vision, and agentic tasks. But it is not available to the public.

Mythos is being deployed exclusively through Project Glasswing — Anthropic's defensive cybersecurity initiative — to a restricted set of enterprise partners including AWS, Apple, Cisco, Google, JPMorgan Chase, Microsoft, Nvidia, and CrowdStrike. The model has deliberately higher cybersecurity capabilities than Opus 4.7, which is why access is restricted. Anthropic is testing new cyber safeguards on less capable models first before expanding access to frontier systems.

The practical implication: if you are a regular user or developer, Opus 4.7 is the ceiling you can actually access. Mythos exists, it is better, and it is not for general availability — yet.

Claude 4 vs GPT-5: The Honest Comparison

This is the question most people actually want answered.

Coding — Claude Opus 4.7 leads. Its 64.3% on SWE-bench Pro is the highest score of any publicly available model, 6.6 points ahead of GPT-5.4's 57.7%. For developers building real production software, Claude has the edge.

Agentic tool use — Claude leads. On MCP-Atlas (the benchmark for AI agent tool invocation), Opus 4.7 leads GPT-5.4 by 9.2 points. Claude is better suited for autonomous workflows, multi-step reasoning chains, and tasks where the AI needs to use tools reliably.

Web browsing and search — GPT-5.4 leads. On BrowseComp (web search accuracy), GPT-5.4 scores 89.3% versus Claude's 79.3%. If web research is your primary use case, GPT-5 has the advantage.

Scientific reasoning — Claude leads. Opus 4.7 scores 94.2% on GPQA Diamond (graduate-level science questions), ahead of GPT-5.4.

Legal and financial analysis — Claude leads. Opus 4.7 posted the highest legal reasoning score of any Claude model and leads on financial tasks like due diligence and market intelligence synthesis.

The honest summary: for coding, agents, and professional knowledge work, Claude 4 is the current benchmark leader. For web search tasks, GPT-5 has an edge. For most everyday use, the difference is marginal and both are excellent.

How to Access Claude 4

claude.ai — The simplest way. Free plan gives you access to Sonnet 4.6 with limits. Claude Pro ($20/month) gives higher limits on Sonnet and some Opus access. Claude Max ($100/month) gives 5x more usage and priority Opus 4.7 access.

The Anthropic API — For developers building applications. Opus 4.7 at $5/$25 per million tokens. Sonnet 4.6 at $3/$15 per million tokens. Haiku 4.5 at lower cost for high-volume tasks.

Amazon Bedrock, Google Cloud Vertex AI, Microsoft Foundry — Claude 4 models are available on all three major cloud platforms, which matters for enterprise teams with existing cloud infrastructure.

Claude Code — Anthropic's terminal-based AI coding agent, included with Claude Pro and Max plans. Defaults to Sonnet 4.6 for most tasks and escalates to Opus 4.7 for the hardest work. It ships with an /ultrareview command that runs Opus 4.7 at maximum reasoning depth on any piece of code.

Which Model Should You Use?

For everyday use — writing, research, analysis, Q&A: Sonnet 4.6 on the free or Pro plan. It handles the vast majority of tasks you will throw at it.

For complex coding and software engineering: Opus 4.7, either through Claude Max or the API. The benchmark improvements over Sonnet are real and meaningful for hard engineering work.

For high-volume applications where you are paying per token: Haiku 4.5 for speed-sensitive, cost-sensitive workloads. Sonnet 4.6 for the balance of capability and cost.

For building AI agents and autonomous workflows: Opus 4.7. Its lead on the MCP-Atlas agentic benchmark is the most relevant signal here.

One practical note: Anthropic is deprecating the original Claude 4.0 model strings on June 15, 2026. If you have 20250514 in any API calls in your codebase, update them to the current model IDs before that date. The current strings are claude-opus-4-7, claude-sonnet-4-6, and claude-haiku-4-5.

The Bottom Line

Claude 4 is the current state of the art from Anthropic — and in coding, agentic tasks, and professional knowledge work, it is leading the field.

The model lineup is straightforward once you understand the tiers: Haiku for speed, Sonnet for daily work, Opus for the hardest tasks. The current flagship is Opus 4.7, released April 2026, and it represents the most capable AI model most people can actually access right now.

If you have not tried Claude and you work with text, code, research, or data in any capacity — it is worth your time.

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