Claude Opus vs Sonnet: Which One to Use, and When Opus Is Worth Twice the Price

Claude Opus 5.5 costs twice as much per token as Claude Sonnet 5.5, and on Anthropic's own benchmarks the two sit within a few points of each other. The real difference in Claude Opus vs Sonnet shows up at the default settings. At the Medium effort level the Claude apps use, Opus 5.5 scores 51.2 on the Artificial Analysis Intelligence Index and Sonnet 5.5 scores 40.8.

That gap decides most of the choice.

This guide compares the current pair, Opus 5.5 (released September 22, 2026) and Sonnet 5.5 (September 28). It covers price, effort, coding and plan access, with Claude Haiku 5.5 as the third option. It ends with a simple rule for which model to pick and when raising the effort level beats switching models.

The Key Takeaways

• Price: Opus 5.5 costs $4 / $20 per million input and output tokens, Sonnet 5.5 costs $2 / $10.
• Top scores are close: at Max effort, Artificial Analysis scores Opus 5.5 at 58 and Sonnet 5.5 at 56, and on Terminal-Bench 4.0 the leader flips depending on who runs the test.
• Defaults are not close: at Medium effort, Opus 5.5 scores 51.2 for $1.34 per task and Sonnet 5.5 scores 40.8 for $0.48.
• The crossover: Sonnet 5.5 at Xhigh costs $2.01 per task for 51.9, while Opus 5.5 at High scores 53.6 for $1.82. Past Sonnet's High setting, switch to Opus.
• Plans: Claude Free includes Sonnet and Haiku but not Opus, which starts on Pro at $20 a month.

Claude Opus vs Sonnet at a Glance

Claude Opus 5.5 is Anthropic's model for long, open-ended work, and Claude Sonnet 5.5 is the faster, half-price model for well-scoped everyday tasks. Both have a 1 million token context window, 128K tokens of output and the same five effort levels. Claude Haiku 5.5 sits below them for high-volume, latency-sensitive jobs. The table compares all three as of October 11, 2026.

Prices come from Anthropic's pricing page, and the latency ratings and defaults from its model documentation. The benchmark rows come from Anthropic's launch posts and the Artificial Analysis Opus 5.5 model page. Our comparison of every Claude model covers the older generations and Fable 5.1, the class above Opus.

What Actually Separates Claude Opus and Sonnet

Judgment on open-ended work separates Claude Opus 5.5 from Claude Sonnet 5.5, not raw benchmark scores. Anthropic's own Sonnet 5.5 launch post says so directly. Sonnet 5.5 is "strongest at well-scoped everyday tasks, fixing bugs, and creating polished documents, slides, and spreadsheets." Opus 5.5 "remains clearly stronger at complex, open-ended work requiring sustained judgment."

The published benchmarks barely show that difference. On GDPval-AA v2.1, a test of real-world work across 44 occupations, Anthropic's launch table puts Sonnet 5.5 at 1844 Elo against 1846 for Opus 5.5. Artificial Analysis, which runs GDPval-AA, currently shows a wider but still modest gap of 1866 to 1838. In Anthropic's tables, Opus 5.5 leads on Humanity's Last Exam with tools (67.7% vs 64.5%), on OSWorld 2.1 computer use (81.8% vs 80.1%) and on CursorBench 4.0 (57.8% vs 55.5%). On Terminal-Bench 4.0, the result depends on who runs it. Anthropic adds a caution of its own: "benchmark scores capture only one facet of a model's capabilities."

Anthropic's two main documents also point readers in different directions. The developer guide to choosing a model says "most workloads start with Claude Opus 5.5." The Sonnet 5.5 launch post presents Sonnet as the everyday default and Opus as the specialist. Both are true at once. The answer depends on the effort setting, and that is where the price comparison starts.

Claude Opus vs Sonnet Price: Twice the Rate, Not Always Twice the Bill

Claude Opus 5.5 costs exactly twice Claude Sonnet 5.5 per token. The cost of a finished task depends on how many tokens each model spends, and that depends on effort. Effort is the setting that controls how long Claude thinks and how many tokens it uses, from Low through Medium, High and Xhigh to Max. Both models offer all five levels, in the API and in the model menu on Claude.ai.

What each effort level costs

Artificial Analysis runs its Intelligence Index v4.3.2 at every effort level and publishes a score and an average cost per task for each. The figures below were read from its leaderboard on October 11, 2026. They measure the index's own mix of tasks, so treat the cost column as a ratio between settings, not as your bill.

Where Opus becomes the cheaper choice

Claude Opus 5.5 becomes the cheaper way to buy intelligence once Sonnet 5.5 is pushed past High effort. Sonnet 5.5 at Xhigh scores 51.9 for $2.01 per task. Opus 5.5 at High scores 53.6 for $1.82, which is both higher and cheaper. Even Opus 5.5 at its default Medium setting comes within a point of Sonnet's Xhigh score (51.2) for two thirds of the cost.

Below that line, Sonnet 5.5 wins. Sonnet at High scores 46.8 for $0.88, and nothing Opus offers is cheaper than that except Opus at Low, which scores lower (42.3 for $0.55). Anthropic describes the same shape in its launch post: Sonnet 5.5 "complements Opus 5.5 best when running at lower effort settings, where it costs less per task. At higher settings, it can perform comparably at a similar cost."

The default settings are where most people meet both models, and there the gap is widest.

In the Claude apps both run at Medium, where Opus 5.5 scores more than 10 points higher at 2.8 times the cost per task. Artificial Analysis also calls both models "very verbose" at Max. Opus 5.5 generated 260 million tokens to complete the index and Sonnet 5.5 generated 420 million, against a median of 82 million. Our explainer on what AI tokens are shows how token counts turn into a bill.

When to Use Claude Opus vs Sonnet

Use Claude Sonnet 5.5 when the task is well defined and easy to check. Use Claude Opus 5.5 when the task is ambiguous, long or expensive to get wrong. The table turns that rule into specific jobs.

Before switching models, try changing the effort level. Anthropic's model guide says "tuning effort is often a better lever than switching models." In practice, try Sonnet 5.5 at High before paying for Opus. Try Opus 5.5 at Low before ruling Opus out on cost.

Low-effort Opus is stronger than its name suggests. Carl Bennett, CIO of Deloitte Consulting, is quoted in Anthropic's Opus 5.5 launch post: "Even at its lowest effort setting, Claude Opus 5.5 caught 72% of known bugs in our code reviews to Opus 5's 56% at high effort, with fewer false alarms and a fraction of the output."

Claude Opus vs Sonnet for Coding

For coding, Claude Sonnet 5.5 is the better value for scoped work and Claude Opus 5.5 is better for large, uncertain projects. The benchmarks do not split as cleanly as that advice suggests.

What the coding benchmarks show

Terminal-Bench 4.0, the headline agentic coding test for both models, does not pick a clear winner. In the comparison table of Anthropic's Sonnet 5.5 launch post, Sonnet 5.5 scores 70.6% against 66.4% for Opus 5.5, which Anthropic ran at Xhigh effort. Artificial Analysis also has Sonnet ahead at Max effort, 63.6% to 59.6%. The public Terminal-Bench 4.0 leaderboard, run in Claude Code at Max effort, has it the other way. Opus 5.5 scores 64.8% and Sonnet 5.5 scores 61.8%, with 95% confidence intervals of about three points on each.

The same leaderboard shows what the Sonnet result costs at the top setting. Its Sonnet 5.5 run used 19.4 billion tokens and cost about $7.3k, against 8.0 billion tokens and about $4.7k for Opus 5.5. That Sonnet cost was priced before Anthropic halved Sonnet 5.5's cache-read price on October 7, so a run today would cost less. On the two other coding tests Anthropic publishes, Opus leads: 54.4% against 52.1% on FrontierCode 1.1 (Sonnet at Xhigh) and 57.8% against 55.5% on CursorBench 4.0. Anthropic says Sonnet's best CursorBench score is "within about two points of Opus 5.5."

The gap between the two models on coding tests is small, and the gap in cost per task depends on effort. For bug fixes and features with a clear specification, Sonnet 5.5 gets close to Opus results at half the token price. For work where the hard part is understanding a large system, Anthropic's biggest examples use Opus. One early tester used Opus 5.5 to audit and fix a 200,000-line codebase in under three hours, where Opus 5 took more than 20.

Opus and Sonnet in Claude Code

Claude Code already picks Opus for you. Its model configuration docs say the default model is Opus 5.5 on Pro, Max, Team, Enterprise and the Anthropic API. Opus 5.5 and Sonnet 5.5 both start at Medium effort. To spend less on scoped work, switch to Sonnet 5.5 with the /model command and change effort with /effort.

Claude Code also has a setting that uses both. The opusplan model alias runs Opus in plan mode "for complex reasoning and architecture decisions." In execution mode it switches to Sonnet "for code generation and implementation." That split matches Anthropic's own advice: Opus for the judgment, Sonnet for the scoped work that follows.

Three commands cover most of it in a Claude Code session. The first moves scoped work to Sonnet at half the token price, the second lets Opus plan while Sonnet writes the code, and the third raises effort before you switch models at all:

/model sonnet
/model opusplan
/effort high

Two more details matter in Claude Code. Opus 5.5 has a fast mode at $8 / $40 per million tokens, with up to 2.5 times the output speed. Both models also run safety classifiers. When one flags a cybersecurity request, Sonnet 5.5 re-runs it on Sonnet 5 and Opus 5.5 re-runs it on Opus 4.8, and Anthropic says routine secure-coding work is unaffected.

Where Claude Haiku Fits

Claude Haiku 5.5 beats both Opus and Sonnet when a task is simple, repeated many times, or needs the fastest response. It costs $0.10 / $0.50 per million tokens for prompts up to 100,000 tokens, a twentieth of Sonnet 5.5's input price. Anthropic's model overview rates it the fastest current Claude model.

In Anthropic's tables, Haiku 5.5 scores 1620 on GDPval-AA, well below Sonnet 5.5's 1844, and 39.2% on Terminal-Bench 4.0 against Sonnet's 70.6%. Anthropic's Haiku launch post says Sonnet and Opus "remain better choices for complex agentic coding tasks." It recommends Haiku for summaries, classification, database queries and subagent work under a larger model. Our Claude Haiku 5.5 guide covers its benchmarks and when it beats Sonnet.

Which Claude Plans Include Opus and Sonnet

Claude Sonnet 5.5 is on every Claude plan including Free, while Claude Opus 5.5 needs Pro or above. Pro costs $20 a month, or $17 a month billed annually, according to Anthropic's pricing page on October 11, 2026. Max 5x starts at $100 a month.

The model you pick also affects how long your plan lasts. Anthropic's usage guidance lists model choice and effort level among the factors that drain usage limits. Its settings guide warns that higher effort uses more tokens, "so you'll reach your usage limits faster."

Anthropic does not publish how much faster Opus drains a session than Sonnet. Our guides to Claude usage limits and Claude Pro vs Max explain the session and weekly meters.

In the Claude apps, both models live in the model menu next to the send button, which also holds the effort selector. Each model's recommended level is marked "Default." Thinking cannot be turned off on Opus 5.5 or Sonnet 5.5, so effort is the setting that controls how much either model thinks.

Compare Claude with other models without a plan upgrade

If the real question is whether a stronger model would answer your prompt better, the quickest test is to ask the same prompt twice and compare. Fello AI puts Claude in one picker next to GPT, Gemini, Grok and DeepSeek on Mac, iPhone and iPad. You can run that comparison in one conversation before deciding whether a bigger Claude plan is worth it. It has a free tier to start.

The Verdict on Claude Opus vs Sonnet

On a paid plan, make Claude Opus 5.5 at Medium effort your default. At the settings the Claude apps use, it scores about 10 points higher than Sonnet 5.5, and Claude Code already picks it for you.

Drop to Claude Sonnet 5.5 for scoped tasks, high-volume work, or weeks when your usage limit runs short. Never push Sonnet past High effort: Opus at High scores more for less per task than Sonnet at Xhigh. On the Free plan, Sonnet 5.5 is the strongest Claude model you can use, and for most writing, research and scoped coding it is enough. For Opus 5.5 alone, our Claude Opus 5.5 guide covers its launch, pricing and system card.

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