Claude Opus 5 vs Sonnet 5

Claude Opus 5 vs Sonnet 5 is not a choice between a model that can code and one that cannot. Both have a native 1-million-token context window, 128,000 maximum output tokens, adaptive thinking, vision, and tool use. The useful difference is where each model sits on the capability-cost curve.

For most daily coding, start with Claude Sonnet 5. Escalate to Claude Opus 5 when the task is ambiguous, crosses architectural boundaries, or is expensive to correct after a plausible but wrong implementation. That routing rule is more economical than choosing one model for every turn.

Claude Opus 5 vs Sonnet 5 at a glance

The short version is Sonnet by default, Opus by exception. The exception should be a task signal you can describe, not a feeling that the larger model must always be safer.

Specifications and prices

Prices are USD per million tokens before cache, long-context, fast-mode, or tool charges. Anthropic's Sonnet 5 introductory price runs through August 31, 2026; the $3 / $15 standard rate begins September 1. OmniaKey rates are the listed gateway rates checked on the fact-check date. Verify current prices in the model catalog before budgeting production use.

The equal context and output limits matter. Choosing Sonnet no longer means accepting a smaller advertised working window, and choosing Opus does not buy more raw context. Opus buys a stronger underlying model for the evidence already inside that window.

Where Sonnet 5 is the better coding model

Sonnet 5 is the better default when the task is clear enough that execution matters more than rare-pattern recognition. Typical examples include:

• implementing a scoped feature with explicit acceptance criteria;
• fixing a reproduced bug in a familiar part of the repository;
• adding tests around an existing interface;
• reviewing a focused pull request;
• translating an approved design into code;
• running high-volume search, summarization, or maintenance agents.

Anthropic describes Sonnet 5 as its most agentic Sonnet and says it improves reasoning, tool use, coding, and knowledge work over Sonnet 4.6. Its launch materials also report that higher-effort Sonnet 5 can match Opus 4.8 on some tasks. That does not make Sonnet 5 equal to Opus 5 everywhere, but it does raise the amount of ordinary engineering work that can stay on the cheaper model.

Sonnet is especially attractive when the acceptance test is deterministic. If tests, type checks, a build, or a screenshot can reject a weak result quickly, the cheaper model gets repeated chances to prove it is enough.

Where Opus 5 earns the premium

Opus 5 is the better choice when the costly part of the work is choosing the right explanation or design, not producing lines of code. Escalation signals include:

• the obvious fix treats a symptom while the root cause crosses several services;
• requirements are incomplete and the model must surface hidden constraints;
• a migration or architecture decision will be difficult to reverse;
• a broad refactor must preserve behavior that is not captured by tests;
• the change touches authentication, billing, permissions, or durable data;
• Sonnet read the right evidence, made a serious attempt, and still reached the wrong conclusion.

Anthropic positions Opus 5 for long-running, multi-step agent work and reports leading results on its Frontier-Bench and CursorBench coding evaluations. Those are vendor-reported results, not proof that Opus wins on every repository. The detailed methodology, independent evidence, and limitations are covered in our Claude Opus 5 review rather than repeated here.

Use Opus at the point where failure is expensive. Once the architecture is settled or the root cause is known, moving routine implementation back to Sonnet often preserves quality while lowering spend.

What the price difference means per task

Per-token pricing is easy to compare, but completed-task cost is what matters. Consider one uncached agent task that uses 100,000 input tokens and 20,000 output tokens:

This simplified example excludes prompt caching, tool charges, long-context pricing, and retries. It also assumes both models use the same number of tokens, which real agents often do not.

Opus can still be cheaper per accepted change if Sonnet needs several failed attempts, sends a developer down the wrong path, or produces a migration that must be reversed. Sonnet wins when both models pass the same acceptance test with similar human correction. Measure the whole task instead of multiplying only the published rate.

Model versus effort

Model and effort correct different failure modes.

Change from Sonnet to Opus when the model tried properly but lacked capability. It had the relevant files and tools, investigated the problem, ran the checks, and still misunderstood the system or chose the wrong design.

Raise effort when the selected model stopped too early. It skipped a file, avoided a difficult branch, failed to run tests, or returned before verifying the result.

Fix context before changing either control. A vague request, stale repository guidance, missing logs, or unavailable test environment can defeat both models. Paying for Opus does not make absent evidence appear.

Anthropic recommends starting with each model's default effort. Higher effort controls more than private reasoning: it can increase the files read, tools used, steps completed, and verification performed. Compare models at the same default first, then tune effort on the model you plan to use.

A practical Sonnet-to-Opus routing policy

Use clean task boundaries rather than switching models after every imperfect response:

1. Start routine feature, maintenance, and review work on Sonnet 5 at its default effort.
2. Define the acceptance test before the model edits code.
3. Retry Sonnet only when the failure came from missing context or insufficient effort.
4. Move to Opus when Sonnet had the evidence, tried seriously, and still failed on capability.
5. Keep Opus for the architectural decision, root-cause analysis, or highest-risk implementation.
6. Return to Sonnet when the remaining work becomes explicit and mechanical.

This policy avoids two common wastes: paying Opus rates for trivial turns and forcing Sonnet through a problem it repeatedly cannot solve.

Switching in Claude Code

After configuring the Anthropic-compatible endpoint with the Claude Code setup guide, use exact model IDs for reproducible comparisons:

/model claude-sonnet-5
/model claude-opus-5

Use a fresh session or a clean task boundary when comparing. Switching halfway through a long conversation makes the next model consume the inherited history, which changes latency and cost and can obscure which model actually solved the problem.

The broader Claude Code model-selection guide also covers Fable and Haiku. This page deliberately keeps the narrower Opus-versus-Sonnet decision.

How to compare them on your repository

Build a small evaluation set from work your team actually accepts or rejects:

Run each task more than once because agent outcomes vary. Record input, cache, and output tokens; elapsed time; tool calls; human correction minutes; and whether the final change passed the same acceptance test.

Do not change model, effort, prompt, and permissions in one comparison. If all four move, the result cannot tell you why one run succeeded.

Final recommendation

Choose Claude Sonnet 5 for daily coding, bounded implementation, routine review, and high-volume agent work. It offers the same 1M context and 128K output ceiling as Opus 5 at a lower token price.

Choose Claude Opus 5 for ambiguous debugging, architecture, long autonomous work, and changes where a convincing mistake is expensive. Use it as an escalation path, then let your accepted-change data decide whether any workload deserves Opus by default.

Frequently asked questions

Is Claude Opus 5 better than Sonnet 5 for coding?

Opus 5 is the more capable model and is the stronger starting point for difficult, ambiguous, or high-risk coding tasks. Sonnet 5 is usually the better default for routine work because it is cheaper and designed as a strong generalist. Neither is the best choice for every task.

Does Opus 5 have more context than Sonnet 5?

No. Both models have a native 1-million-token context window and up to 128,000 output tokens. Opus provides more capability, not a larger advertised window.

How much more expensive is Opus 5?

Anthropic lists Opus 5 at $5 input and $25 output per million tokens. Sonnet 5 is $2 / $10 through August 31, 2026 and $3 / $15 from September 1. Actual task cost also depends on token use, caching, tools, retries, and human correction.

Should I use Opus 5 for every Claude Code task?

No. Start with Sonnet for routine work and move to Opus when ambiguity, capability limits, or failure cost justify it. Keeping Opus on every simple turn increases spend without guaranteeing a better accepted result.

Can high-effort Sonnet 5 replace Opus 5?

Sometimes. Higher effort can make Sonnet investigate and verify more thoroughly, and Anthropic reports that high-effort Sonnet 5 can match Opus 4.8 on some tasks. It does not change Sonnet into Opus 5. Escalate when Sonnet had the right evidence and effort but still lacked the capability to solve the task.

Sources checked

• Introducing Claude Sonnet 5
• Introducing Claude Opus 5
• What's new in Claude Sonnet 5
• What's new in Claude Opus 5
• Claude models overview
• Anthropic API pricing
• Choosing a Claude model and effort level in Claude Code
• Claude Code model configuration