Claude Opus 5.5 vs Sonnet 5.5: $4 vs $2, and what else differs

Claude Opus 5.5 vs Sonnet 5.5 comes down to price and speed: Opus costs twice as much per token, and Sonnet is faster. On Anthropic's published specs the two models match on context window, output limit and knowledge cutoff. This comparison is based on the products' docs and published results, not our own testing.

Anthropic's models overview describes Opus 5.5 as the model "for long-running agentic coding and knowledge work" and Sonnet 5.5 as "the best combination of speed and intelligence." It tells API users to start with Opus 5.5 for most workloads.

Specs side by side

Source: Anthropic's models overview, October 30, 2026. Anthropic notes the latency row is relative to the current lineup and that real speed depends on prompt length, output length and thinking effort.

How they differ in practice

Price is the clearest gap. A job that reads 1 million tokens and writes 100,000 costs $6 on Opus 5.5 and $3 on Sonnet 5.5 at list price, before batch discounts or caching. Cache reads are $0.20 per million on Opus and $0.10 on Sonnet.

Thinking works differently. Opus 5.5 always thinks, and the model decides how much, steered by the effort setting, which defaults to medium. Sonnet 5.5 also uses adaptive thinking with a high default effort. Anthropic's Models API reports that Sonnet 5.5 does not accept thinking: {type: "disabled"}, so you cannot switch thinking fully off on it.

What independent benchmarks show

On the Artificial Analysis Intelligence Index v5, we reported Opus 5.5 leading at 58. We did not find a Sonnet 5.5 score in the sources we read, so we do not rank the two on benchmarks here. Run your own tests on your own prompts before you pick.

Cost with caching and batch

Both models use the same discount rules, expressed differently. Anthropic's overview says Batch API requests are 50% off, and that cache reads cost 5% of the base input price on Opus 5.5 and Sonnet 5.5. That matches the pricing page: $0.20 per million cached input tokens on Opus and $0.10 on Sonnet. Cache writes with the 5-minute lifetime cost $5 on Opus and $2.50 on Sonnet.

For an agent that resends a long prompt many times, the cache read price is the number that matters. Reading a million cached tokens costs $0.20 on Opus and $0.10 on Sonnet, against $4 and $2 for the same tokens uncached.

Where each model runs

Both models are offered under the same IDs on the Claude API, Microsoft Foundry, Claude Platform on AWS and Claude Models on Google Cloud. On Amazon Bedrock the IDs are anthropic.claude-opus-5-5 and anthropic.claude-sonnet-5-5. Anthropic's retirement commitment applies to platforms it operates, and partner platforms set their own dates.

In the Claude app

Anthropic's pricing page lists both Opus and Sonnet on Pro, Max, Team and Enterprise, and only Sonnet on the Free plan. It does not give version numbers in that table, so confirm in the model picker which version your plan offers. Usage on paid plans is counted in 5-hour sessions, and Anthropic says Pro gives at least 5 times the usage of Free in each one. The pages we read give no ratio for how fast each model uses that allowance.

What this comparison leaves out

We did not test either model, and we did not find an independent score for Sonnet 5.5, so there is no benchmark verdict here. Anthropic's pages also give no figure for how much better Opus is on any task. The honest summary is that the specs are close, the price is not, and the quality gap is something to measure on your own work.

Which one to choose

• Choose Sonnet 5.5 for high-volume work where speed and cost matter, such as chat features, extraction and routing steps.
• Choose Opus 5.5 for long agentic coding runs and hard knowledge work, where Anthropic points its own recommendation.
• Use Opus on Pro, Max, Team or Enterprise plans in the app. The Free plan has Sonnet only, as we explain in Is Claude Opus 5.5 free.

Both models share a one million token window, so context size will not decide it. Cost per finished task will, and that is something only your own evals can show.