Claude Sonnet 5.5 vs Opus 5.5: Which One Should You Use? Pricing, Benchmarks and a Routing Rule

Claude Sonnet 5.5 and Claude Opus 5.5 are the two models most people will choose between this autumn, and the choice is mostly about money. Opus 5.5 lists at exactly twice the price of Sonnet 5.5 per token. Whether that doubled price buys you anything depends on the task, and the benchmark numbers circulating online will not settle it, because they disagree with each other.

This guide covers what Anthropic's launch coverage confirms, how the two models compare on price and on third-party benchmarks, and a simple routing rule for deciding which to use. It also covers what changed since the earlier Sonnet 5 vs Opus 5 comparison, because many pages still describe the older pair. Figures were checked on October 17, 2026. We could not open Anthropic's own launch posts directly, so the vendor figures below come from coverage that cites them and are labelled as claims. Confirm current prices on Anthropic's models overview before you budget.

Claude Sonnet 5.5 vs Opus 5.5 at a glance

Sources for the table: the Gradually comparison, DataNorth's Opus 5.5 report and LLM Reference. Sonnet 5.5's maximum output was not stated in what we found. Batch processing is listed at half price for Sonnet 5.5, which matters for bulk jobs.

What Anthropic says about each model

These are vendor claims, relayed by the coverage cited, and not independent tests.

Opus 5.5 is described as costing about 40 percent less than Opus 5 on typical work, with output more than 30 percent faster, and Anthropic reports better token efficiency on large codebases. DataNorth's summary of the launch says Opus 5.5 matches or beats the more expensive Fable 5.1 on most published benchmarks, and that Anthropic's documentation now recommends Opus 5.5 for most workloads, with Fable 5.1 reserved for the most demanding reasoning and long agent tasks. Fable 5.1 lists at $10 input and $50 output per million tokens.

Sonnet 5.5 is described as more than 30 percent faster than Sonnet 5, with typical work costing up to 30 percent less, according to Let's Data Science's launch report. Anthropic positions it for well-scoped tasks, and says routine software development is unaffected by its new cybersecurity safeguards.

A small piece of arithmetic worth doing: Opus 5.5's list price is $4 against Opus 5's $5, which is only 20 percent lower. So the rest of the claimed 40 percent saving has to come from using fewer tokens per task, not from the price list. That is plausible, but it is a claim to test on your own workload, not a certainty.

What the two models cost

Sources differ on whether Sonnet 5.5's price is a cut from Sonnet 5's standard rate or the same as its introductory rate, so check the live page before comparing.

Here is what that means for a made-up monthly workload of 10 million input tokens and 2 million output tokens, using list prices only and ignoring caching and batch discounts:

The pattern is simple. Opus 5.5 is exactly twice Sonnet 5.5 on input and on output, so the question is whether a given task is worth double.

What the benchmarks say, and why one number is not enough

Anthropic's launch post reports Opus 5.5 at 66.4 percent on Terminal-Bench 4.0, according to DataNorth. The independent index run by Artificial Analysis, as collected by Gradually, shows the same model at 59.6 percent on its own version of Terminal-Bench 4.0. Same model, same benchmark name, a gap of almost seven points. The difference is setup: the agent, the reasoning level and the harness all change the score.

That is the main reason to distrust any single percentage, including the ones below. They come from Gradually's comparison, which collects third-party results, with data dated October 13 to 15, 2026:

Read it as a pattern, not a verdict. Opus 5.5 leads the knowledge and reasoning measures, and Sonnet 5.5 leads several agent and terminal tasks. Gradually itself says winning one benchmark is not an overall verdict, and notes that some pairs use different reasoning levels or output limits. Treat gaps of a point or two as noise.

The routing rule that matters more than any score

Default to Sonnet 5.5 and escalate to Opus 5.5 when you cannot cheaply check the result yourself.

• Use Sonnet 5.5 for: bug fixes, test generation, drafting, summaries, spreadsheet and slide preparation, and bulk work where a wrong answer is easy to spot.
• Use Opus 5.5 for: architecture decisions, changes that span many files, long-running agent jobs, ambiguous requirements, and anything where an unnoticed error is expensive.
• Use Fable 5.1 only if Opus 5.5 fails your own test on the hardest reasoning or long-horizon work. At $10 and $50 it is two and a half times Opus 5.5.

The rule sidesteps the benchmark confusion. You do not need to know whether Sonnet scores 56 or 63 on a test. You need to know whether a wrong answer would be obvious. For developers choosing tools around the model, our guide to AI tools for professional developers covers the surrounding data, and tools such as Cursor and GitHub Copilot let you switch models per task.

What changed since Sonnet 5 vs Opus 5

If you read the earlier Sonnet 5 vs Opus 5 comparison, this is what moved:

One more comparison that surprised us: on Gradually's Sonnet 5.5 vs Opus 5 page, Sonnet 5.5 scores slightly higher than the previous-generation Opus 5 on the Vals Index (67.0 against 63.7) at less than half the list price. A newer Sonnet can beat an older Opus, so upgrade the Sonnet tier before you pay for the top tier. Anthropic's earlier release notes also compared each model with its predecessor rather than head-to-head, a gap that DataCamp's Sonnet 5 vs Opus 5 piece pointed out in August.

A caveat for security and biology work

Per DataNorth's summary, Opus 5.5 was evaluated with production safeguards switched on. When those safeguards stepped in, cybersecurity tasks were completed by Opus 4.8 and biology tasks by Opus 5, and Anthropic says this likely lowered the published scores on those benchmarks. If your work sits near that boundary, such as security research or biology tooling, published scores may not reflect what you will see, so test before you switch.

Which should you pick?

How to test both on your own work

1. Pick ten real tasks. Use work you already did, so you know the correct answer.
2. Run both models. Same prompt, same settings, one attempt each.
3. Score blind. Have someone grade the outputs without knowing which model wrote them.
4. Track tokens. Record input and output tokens per task, since Anthropic's cost claims rest on efficiency.
5. Compare cost per good answer. Divide cost by the number of acceptable results, not by the number of calls.

If Sonnet 5.5 passes most of your tasks, route to it by default and keep Opus 5.5 for the rest. Check the data terms on whatever plan you use, because training defaults differ by plan, as our AI tool contract checklist explains.

Final thoughts

The honest answer to "Sonnet 5.5 or Opus 5.5" is that the third-party numbers cannot decide it for you. The same model scores differently depending on who runs the test, and the gaps between these two are often small. What holds up is the price: Opus 5.5 costs twice as much, so it should earn that premium on tasks where a hidden mistake is expensive.

Use Sonnet 5.5 by default, escalate on purpose, and re-run your ten tasks whenever a new model ships. To keep exploring, browse our AI chatbots category, read our guide to the best AI chatbots, or see the Claude listing.