Claude Sonnet 5.5 is the sensible lower-cost baseline in this pairing. Evaluate Opus 5.5 when difficult coding or knowledge work produces costly failures with that baseline. The decision should depend on accepted results and reviewer time, not the assumption that the premium model wins every task.
Researched and written by GPT, an AI, from primary documentation checked November 3, 2026. The recommendations are editorial assessments. No hands-on performance test is claimed; numerical examples are calculations under the stated assumptions.
Sources checked November 3, 2026.
“Opus vs Sonnet” describes model families. This comparison fixes the versions at Opus 5.5 and Sonnet 5.5, checked November 3, 2026. Earlier versions have different limits, prices and retirement dates. The Claude app’s subscription allowance is also a different purchase from API tokens. Anthropic’s current model overview.
What paying twice as much buys—and does not prove
The standard API rates are $4 per million input tokens and $20 per million output tokens for Opus, versus $2 and $10 for Sonnet. A hypothetical batch with two million uncached input tokens and 500,000 billed output tokens therefore costs $18 on Opus or $9 on Sonnet. This calculation excludes caching, tools, discounts, retries and taxes. Reasoning can contribute to billed output, so compare billed usage rather than only the final answer’s length. Opus pricing and Sonnet pricing.
For a production workflow, a $9 saving is irrelevant if it creates an hour of correction work. Conversely, paying twice the rate is wasteful if both pass the same checks. Neither outcome has been measured here. A support classifier, a code migration and a financial-document extraction pipeline need different acceptance tests.
Their headline context limits are the same
Both list a one-million-token context window and 128,000 maximum standard output tokens. Both accept text and images and return text. A large input ceiling means material can fit; it does not establish that every fact will be retrieved correctly or that a long answer will remain coherent.
Anthropic positions Opus for long-running agentic coding and knowledge work and Sonnet for a balance of speed and intelligence. Those descriptions are vendor positioning. Its comparative latency labels are not independent stopwatch measurements under your workload. Model specifications.
Integration differences can decide the migration
Opus 5.5 uses always-on adaptive thinking. Sonnet 5.5 supports a between_tools setting that turns off up-front thinking at supported effort levels. This is not a promise of identical behavior with thinking “off.” Both versions also introduce compatibility changes around forced tool use and thinking blocks; copying an older integration without checking the migration documentation can produce errors.
A useful evaluation is a real repository change: give both models the same starting commit, issue description, tools and budget. Check the requested behavior, regression tests, unrelated edits and explanations of uncertainty. Record effort settings, token bills, retries and human correction time. Preserve failed patches as well as successful ones.
When the recommendation changes
Choose Sonnet when it meets the acceptance threshold and the lower rate matters at your volume. Consider routing only ambiguous or high-cost failures to Opus instead of sending everything there. Choose Opus when your own evaluation demonstrates a meaningful reduction in errors or repair work that covers its extra cost.
If the application depends on forcing a particular tool call or reusing thinking blocks between models, resolve compatibility before comparing quality. A model that scores well in a benchmark can still be the wrong replacement for an integration it breaks. For a new deployment, confirm the current model IDs and retirement commitments again at launch.
Model references
Anthropic · Model library
Claude Opus 5.5
AvailableExact Opus version used for this API and workflow comparison.
Author’s assessment; check the guide’s evidence and limitations.- Access
- API
- Input
- text, image
- Output
- text
- Context window
- 1,000,000 tokens
Catalog checked . Model specifications do not establish access through a particular app or subscription.
Anthropic · Model library
Claude Sonnet 5.5
AvailableExact Sonnet version used as the lower-cost comparison baseline.
Author’s assessment; check the guide’s evidence and limitations.- Access
- API
- Input
- text, image
- Output
- text
- Context window
- 1,000,000 tokens
Catalog checked . Model specifications do not establish access through a particular app or subscription.
