Claude Opus vs Claude Sonnet: when the bigger model is worth it

Claude Opus vs Sonnet, as of October 2026, means Claude Opus 5.5 (released September 22, 2026) against Claude Sonnet 5.5 (released September 28, 2026). Above them sits Claude Fable 5.1, Anthropic's most capable model open to all customers, and below them Claude Haiku 4.5. This page compares the two models you are most likely to pick between in the Claude app or the API, using only Anthropic's own documentation and announcements. Every benchmark number below is quoted from Anthropic's pages.

Short verdict: which model for which job

• Everyday coding, writing and analysis: Sonnet 5.5. Anthropic's selection guide lists code generation, data analysis, content creation, visual understanding and agentic tool use as its starting use cases.
• Multi-hour agents and large refactors: Opus 5.5. The same guide lists multihour autonomous coding agents, large-scale refactoring, complex systems engineering, vision-heavy workflows and computer use.
• Open-ended work that needs judgment: Opus 5.5. In the Sonnet 5.5 announcement, Anthropic writes that Opus 5.5 is "clearly stronger at complex, open-ended work requiring sustained judgment."
• Cost-sensitive or high-volume API use: Sonnet 5.5, at half the per-token price.
• Claude's free plan: Sonnet only. Opus starts at Claude Pro.
• The hardest tasks: neither. Anthropic points to Fable 5.1 when Opus 5.5 at high effort still falls short.

Spec table, from Anthropic's docs

Both models accept text and images and return text. Batch API requests are 50% off for both. Fast mode on Opus 5.5 gives up to 2.5x higher output speed at premium pricing, according to Anthropic's model selection guide.

Anthropic's published benchmarks, side by side

These figures come from the comparison table in Anthropic's Sonnet 5.5 announcement. They are the vendor's own numbers, measured at different effort settings, so treat them as a rough guide.

The pattern is close scores with Opus ahead on most rows. Anthropic's footnotes say the Opus Terminal-Bench figure is its best score at Xhigh effort and that Sonnet 5.5 scored lower at Max effort than at Xhigh on FrontierCode. Anthropic also says Sonnet 5.5 at Max effort performs comparably to Opus 5.5 on several evaluations, and that Sonnet complements Opus best at lower effort settings, where it costs less per task; at higher settings the two can perform comparably at a similar cost. In other words, Sonnet's price advantage is largest on routine work.

Which is better for writing, coding, research and images

Coding

Anthropic's selection guide says most workloads start with Opus 5.5, and it lists Sonnet 5.5 for speed and capability on everyday coding. For routine coding, Sonnet is the cheaper pick: it is fast, half the price, and close to Opus on CursorBench, which Anthropic describes as tasks taken from real Cursor sessions. Opus 5.5 leads on FrontierCode, which checks whether a change could be merged without human edits, and Anthropic aims it at multihour agents and large refactors. In Claude Code, Anthropic sets the default effort to medium. Our Claude Code prompts work with either model, the Claude Code vs Codex page covers the agent itself, and our Claude Code cheat sheet collects day-to-day commands for either model.

Writing

Anthropic lists content creation among Sonnet 5.5's use cases. For routine drafts, Sonnet's speed and price are the practical draw. For long pieces that require holding many constraints at once, Opus's lead on knowledge-work tests is small but consistent. Test both with the first prompt below.

Research and analysis

Both read up to 1M tokens. Sonnet is listed for data analysis; Opus is listed for complex reasoning and tasks where accuracy outweighs cost. For multistep deep research carried through to a finished document, Anthropic's guide points to Fable 5.1.

Images

Both models read images and answer in text; neither generates images. Anthropic lists vision-heavy workflows under Opus and visual understanding under Sonnet.

Using both together

You do not have to pick one for good. Anthropic's model guide describes two ways to mix models: an executor that hands hard decisions to a stronger advisor, and an orchestrator that delegates bulk work to lower-cost workers. In practice that can mean Sonnet 5.5 doing most of the steps while Opus 5.5 handles planning and the final review, which keeps the bill closer to Sonnet's rates. The guide also suggests tuning the effort setting before switching models, since effort trades intelligence for speed and cost inside one model.

Same prompt in both: run it and compare

In the Claude app on a paid plan you can switch models per chat, so this test takes a few minutes. We do not print outputs. Run each prompt once with Opus 5.5 and once with Sonnet 5.5 and compare quality against the time you waited.

I want you to act as a strategy analyst. Here is my situation: [describe the decision, the constraints and the deadline]. List the three strongest options, the main risk of each, and what would have to be true for each to be the right choice. Then recommend one and say what evidence would change your mind.

I want you to act as a senior engineer. Plan a refactor of [module or service] so that [goal, e.g. it can be tested without the database]. Break it into steps that each leave the code working, name the files each step touches, and list the tests to add before step one.

If Sonnet's answer is good enough, you have saved half the cost. If Opus catches a risk Sonnet missed, that is the kind of task to route to Opus. Our Claude prompts library and the Claude prompt generator have more to test with.

Pricing and plan access

Anthropic's announcement says Opus 5.5's prices are 20% lower than Opus 5's. For comparison, Fable 5.1 is $10 and $50 per million tokens and Haiku 4.5 is $1 and $5. To see how Claude stacks up against OpenAI's lineup, read ChatGPT vs Claude.

FAQ

Is Claude Opus better than Sonnet?

On most of Anthropic's published tests, Opus 5.5 scores higher, but by small margins, and Sonnet 5.5 leads on Terminal-Bench 4.0. Anthropic says Opus 5.5 is clearly stronger at complex, open-ended work. Sonnet 5.5 is faster and half the price.

Which is better for coding, Opus or Sonnet?

Sonnet 5.5 for everyday coding and agentic tool use; Opus 5.5 for multihour agents, large refactors and complex systems work. On CursorBench 4.0 they score 55.5% and 57.8%.

Can I use Opus on the free Claude plan?

No. Claude's pricing page lists Sonnet and Haiku on Free and Opus from Pro.

What is the latest Claude Opus and Sonnet?

As of October 2026, Claude Opus 5.5 (September 22, 2026) and Claude Sonnet 5.5 (September 28, 2026). Claude Fable 5.1 is Anthropic's most capable generally available model.