Introduction

Claude 4 Sonnet and Claude 4 Opus are Anthropic’s latest AI models (released May 22, 2025). Both belong to the Claude 4 generation but serve different needs. Claude 4 Opus is described as Anthropic’s most powerful model, excelling at complex, long-running tasks (especially coding).

Claude Sonnet 4 is a significant upgrade over the earlier Claude 3.7 Sonnet, offering high-performance reasoning and coding in a faster, more cost-efficient package. This comparison will clarify their specifications, performance benchmarks, access options, and ideal use cases, helping readers understand when to use Sonnet vs Opus and how they stack up against other frontier models.

Claude Sonnet 4 is positioned as a general-purpose, high-throughput model. It offers a huge 200K-token context for reading or analyzing long inputs, and can generate large outputs (e.g. lengthy code or documents) quickly. Its pricing is relatively low, making it suitable for cost-sensitive or high-volume applications.

Claude Opus 4, by contrast, is a premium model aimed at the most challenging tasks. It shares the same massive context window, but under the hood is more advanced (Anthropic calls it their “most intelligent model”). Opus 4 is significantly more expensive to use, reflecting its superior capability in deep reasoning and coding. Both models are accessible via API and major cloud ML platforms, but only Sonnet is available to free-tier users (Opus requires a paid plan).

Benchmark results

To see how these models perform, below is a comparison on several standard benchmarks (higher is better in all cases):

Claude Opus 4 continues to lead in general knowledge (MMLU) and math (GSM8K) with the highest scores across the board. However, Claude Sonnet 4 surprisingly outperforms Opus on the SWE-bench (software engineering) benchmark (80.2% vs 79.4%), suggesting it may be better tuned for practical coding tasks.

Google Gemini 2.5 Pro edges ahead on MMMU, a benchmark for multimodal reasoning, while GPT-4o shows balanced but slightly lower scores across most metrics. Overall, both Claude models dominate coding and reasoning tasks, with Sonnet offering exceptional value given its performance.

How to access Claude 4 models

Both Claude 4 models can be accessed via Anthropic’s chat interface (Claude.ai) as well as through an API and integrated services. Claude 4 Sonnet is available to all users for free on the Claude web app (and mobile apps). Free users can chat with Sonnet 4 with some daily rate limits (approximately 100 messages/day). For higher usage and additional features, Anthropic offers paid plans. Claude Pro costs $20/month and includes increased message limits, priority access, and the ability to use “extended thinking” mode (allowing the model to think longer and use tools for complex queries). Pro users also gain access to Claude Opus 4 on the web. Larger plans (Claude Max and Team/Enterprise) provide even greater usage (5× to 20× Pro’s quota) and collaboration features.

Claude 4 Opus is not available on the free tier; it is included in Pro, Max, Team, and Enterprise plans. Developers can directly use both models via the Anthropic API or third-party cloud platforms: Amazon Bedrock and Google Cloud Vertex AI offer Claude 4 Opus and Sonnet as managed models. The API usage is billed per token as noted above, so organizations can choose API access for pay-as-you-go scaling instead of (or in addition to) the chat subscriptions.

Evaluations by Task Type

We ran extensive evaluations across real-world tasks using the Keywords AI gateway. The results highlight practical performance differences between Claude Sonnet 4 and Claude Opus 4, beyond just benchmark scores.

Time to First Token:

Claude Sonnet 4 consistently starts faster, averaging just 1.27 seconds to first token, compared to 1.82 seconds for Opus. This makes Sonnet feel more responsive in interactive applications like coding editors or chat interfaces.

Tokens per Second:

Sonnet also generates outputs much faster—54.84 tokens per second versus 38.93 for Opus. If you care about throughput (e.g., writing long documents, generating large datasets, or responding to multiple users), Sonnet gives you more speed per dollar.

Average Generation Time:

In full responses, Sonnet 4 completes tasks about 30% faster, with an average generation time of 18 seconds, compared to 25.76 seconds for Opus. That means shorter wait times and quicker turnarounds for most use cases.

Coding Tasks

• Sonnet 4 handles typical tasks like writing React components, debugging snippets, and explaining code with speed and clarity. For example, it can write a full-featured login form or suggest bug fixes in seconds.
• However, when dealing with complex refactoring across multiple files or deeply nested logic, it sometimes stalls or loops.
• Opus 4 shines on harder tasks, such as implementing recursive algorithms, coordinating across large codebases, or reasoning through ambiguous spec docs. It's the safer pick when correctness and robustness matter most.

Content Writing Tasks

• Both models are strong at producing blog posts, marketing copy, and emails. Opus offers slightly more nuanced phrasing and coherence over long outputs.
• That said, Sonnet delivers 90–95% of Opus’ quality at a fraction of the cost, making it a more economical choice for most content workflows.

Document Analysis

• We tested both models with long PDFs (up to 100+ pages). Each consistently achieved 95–98% accuracy in extracting key facts, summarizing sections, and answering embedded questions.
• In tasks like analyzing investor reports or parsing legal documents, both models are highly reliable.

Reasoning Tasks

• Opus 4 is clearly superior for complex reasoning, including logic puzzles, long chain-of-thought prompts, and multi-turn deduction.
• Sonnet performs well, but in tricky cases (e.g. nested hypotheticals or math word problems), it can fail silently or misstep, while Opus stays grounded.

Math Tasks

• Both models are nearly tied in accuracy across arithmetic, algebra, and symbolic problems.
• In tests like solving systems of equations or parsing LaTeX-style math, performance is consistent—making Sonnet a capable, fast option.

Best For

Claude 4 Sonnet is ideal for general-purpose and high-volume tasks. Its fast response mode and lower cost make it a great fit for interactive chatbots, customer support assistants, content creation, and daily coding help. It’s especially strong at coding assistance (now powering GitHub’s Copilot coding agent), and excels in short-form reasoning, writing, and analysis tasks where near-instant answers are valuable. Sonnet delivers “frontier performance” in a practical, cost-efficient manner for most applications.

Claude 4 Opus is best for complex, long-running, or mission-critical tasks. It’s the go-to model when you need maximum reasoning depth, such as extensive research analysis, multi-step problem solving, or orchestrating AI “agents” that operate tools over many steps. Opus 4 can work continuously for hours on coding or analytic tasks without losing context. This makes it ideal for large codebase refactoring, elaborate data analysis, or autonomous task agents. If you need the highest accuracy in tricky domains (advanced coding, math, or graduate-level reasoning), Opus is the better choice – it pushes the boundaries further (for example, achieving 90% on a challenging math competition when given extended computation). The trade-off is cost and speed: Opus is slower and pricier, so it’s overkill for simple queries or casual use.

Conclusion

In summary, Claude 4 Sonnet and Opus represent a two-tier approach by Anthropic. Sonnet 4 offers GPT-4-level performance for everyday use at low cost, while Opus 4 targets superhuman-like performance on the hardest tasks (particularly in coding and reasoning) for those willing to invest more. Our comparison shows both models are top-tier – rivaling OpenAI’s GPT-4 and Google’s Gemini – with Opus usually leading by a small margin. For most users and applications, Claude 4 Sonnet will be the sweet spot, providing advanced capabilities without breaking the bank. Power users with demanding projects, however, will appreciate Claude 4 Opus’s extra headroom. Both models expand what’s possible with AI assistants in 2025, whether you need a quick “sonnet” or an in-depth “opus” of answers.