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AI Choice Engine

Model comparison

Claude Opus 5.5 vs Claude Sonnet 5

Two Anthropic tiers compared on the figures that decide which one a workload actually needs.

Catalog record checked September 26, 2026Individual provider fields may changeEvidence confidence: High — see receipts below

Anthropic

Claude Opus 5.5

Frontier

vs

Anthropic

Claude Sonnet 5

Balanced

AI model capability comparison
SpecificationClaude Opus 5.5Claude Sonnet 5
ProviderAnthropicAnthropic
TierFrontierBalanced
Context window1M1M
Max output128K128K
Input / 1M tokens$4Winner: $2
Output / 1M tokens$20Winner: $10
WeightsClosedClosed
ParametersNot disclosedUnverifiedNot disclosedUnverified
Reasoning levelsadaptiveadaptive
Modalitiestext, imagetext, image
API model idclaude-opus-5-5claude-sonnet-5
ReleasedSeptember 22, 2026June 30, 2026
Artificial Analysis Intelligence Index [max] (2026-09-26)Winner: 57.638.2
Humanity's Last Exam [max] (2026-09-26)61.4Not verifiedUnverified
Humanity's Last Exam (2026-06-30)Not verifiedUnverified57.4
Terminal-Bench 4.0 [max] (2026-09-26)59.6Not verifiedUnverified
Terminal-Bench 4.0 [xhigh] (2026-09-22)66.4Not verifiedUnverified
Terminal-Bench 2.1 (2026-06-30)Not verifiedUnverified80.4
SWE-bench Verified (2026-09-01)Not verifiedUnverified79.6
LiveBench (2026-09-05)Not verifiedUnverified76

Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.

Benchmark receipts

Where each score comes from, and how far it can be compared across models.

Pricing tiers

Claude Opus 5.5: $4/$20 per MTok, no long-context surcharge. Cache reads $0.20; 5-minute cache writes $5, 1-hour writes $8. Batch $2/$10; Fast mode $8/$40. Batches API allows 300K output with the output-300k-2026-03-24 beta header. Knowledge cutoff Jun 2026; retirement not before 2027-09-22.

Claude Sonnet 5: Standard $2/$10 per MTok; cache reads 10% of base input. Knowledge cutoff Jan 2026.

FrontierRecord checked September 26, 2026

Claude Opus 5.5

Claude Opus 5.5 is Anthropic's default model for agentic coding and knowledge work — Anthropic says it performs near Fable 5.1 on most work at about 40% lower running cost than Opus 5, and it leads the Artificial Analysis Intelligence Index v4.3.2.

Best for

  • Complex agentic coding
  • Enterprise knowledge work
  • Default frontier model

Watch out

Breaking changes from Opus 5: adaptive thinking cannot be disabled (effort runs low to max, default medium) and forced tool use returns an error. Verbose at max effort, so cap output on cost-sensitive routes.

BalancedRecord checked September 26, 2026

Claude Sonnet 5

Claude Sonnet 5 is Anthropic's best speed/intelligence balance for high-volume agentic work at $2/$10.

Best for

  • Everyday generation
  • High-volume agents
  • Cost-sensitive work

Watch out

A step below Opus 5.5 on the hardest tasks; pick Opus 5.5 when quality is paramount. Sonnet 5.5 is announced but not yet released.

When the cheaper one wins

Claude Sonnet 5 is cheaper on output at $10 per million tokens against $20 for Claude Opus 5.5 — about 2.0×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.

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Evidence confidence: High

How strong and complete the evidence behind this comparison is — not a prediction of which model is better.

  • Pricing verified on both sides — Input and output rates are verified for both models.
  • 4/5 core specs verified on both sides — Not published for at least one side: parameter count.
  • 2 shared named benchmarks with differing scores — Measured on: Artificial Analysis Intelligence Index, Humanity's Last Exam.
  • Verified within the last 90 days — Newest catalog check was 2 days ago.
  • Both models carry source citations — Each side has at least two catalog sources on record.

Source receipts

Each catalog figure was checked against the provider or an independent second source on the date shown.

Related comparisons

Diving deeper on one model? Claude Opus 5.5 · Claude Sonnet 5

Common questions

Claude Opus 5.5 vs Claude Sonnet 5

Answered from the verified figures on this page rather than general guidance.

Is Claude Opus 5.5 or Claude Sonnet 5 cheaper for input?
Claude Sonnet 5 is cheaper at $2 per million input tokens, against $4 for Claude Opus 5.5 — roughly 2.0× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Opus 5.5 has tiered pricing: $4/$20 per MTok, no long-context surcharge. Cache reads $0.20; 5-minute cache writes $5, 1-hour writes $8. Batch $2/$10; Fast mode $8/$40. Batches API allows 300K output with the output-300k-2026-03-24 beta header. Knowledge cutoff Jun 2026; retirement not before 2027-09-22. Claude Sonnet 5 has tiered pricing: Standard $2/$10 per MTok; cache reads 10% of base input. Knowledge cutoff Jan 2026.
Is Claude Opus 5.5 or Claude Sonnet 5 cheaper for output?
Claude Sonnet 5 is cheaper at $10 per million output tokens, against $20 for Claude Opus 5.5 — roughly 2.0× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Opus 5.5 has tiered pricing: $4/$20 per MTok, no long-context surcharge. Cache reads $0.20; 5-minute cache writes $5, 1-hour writes $8. Batch $2/$10; Fast mode $8/$40. Batches API allows 300K output with the output-300k-2026-03-24 beta header. Knowledge cutoff Jun 2026; retirement not before 2027-09-22. Claude Sonnet 5 has tiered pricing: Standard $2/$10 per MTok; cache reads 10% of base input. Knowledge cutoff Jan 2026.
Which has the larger context window, Claude Opus 5.5 or Claude Sonnet 5?
Both accept about 1M tokens of context, so document length will not decide between them.
Do Claude Opus 5.5 and Claude Sonnet 5 support the same reasoning levels?
Yes — both accept the same effort settings: "adaptive". Higher effort costs more and takes longer, so start low and raise it only where output quality actually improves.
Should I use Claude Opus 5.5 or Claude Sonnet 5?
Claude Opus 5.5 is the frontier tier and Claude Sonnet 5 the balanced tier. The useful question is whether your hardest task actually fails on the cheaper one — most production volume such as classification, extraction and summarisation does not.

Next step

Choosing between them

The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.

  • Input price: Claude Sonnet 5 costs $2 per 1M tokens versus $4 for Claude Opus 5.5 — a 2x difference at the headline tier.
  • Measured capability: Claude Opus 5.5 leads Artificial Analysis Intelligence Index 57.6 to 38.2 (measured 2026-09-26).
  • Positioning: Claude Opus 5.5 sits in the frontier tier, Claude Sonnet 5 in the balanced tier — most production volume (classification, extraction, summarisation) does not need the pricier tier.
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