Claude Opus in one minute
Opus is a candidate for tasks requiring substantial coherence, judgement or programming work. Examples include analysing a case file, tracing a change across software components or preparing a reasoned proposal. Greater capability does not automatically mean less checking: flawed sources and unclear goals remain problems.
How does Anthropic position Opus today?
Current API documentation recommends Opus 5.5 as a starting point for most workloads. Anthropic associates it with complex professional work and extended execution. That guidance belongs to this version and documentation; it does not prove that Opus is the best or cheapest choice for everyone.
The relationship with Fable needs nuance. Fable 5.1 focuses on particularly difficult reasoning and work requiring coherence across many steps. Opus 5.5 was released later. Names or version numbers alone cannot reliably rank the families. Documentation mentions Fable when a task still fails your evaluation after increasing reasoning effort in Opus.
For a business, the question is practical: does additional processing produce a more useful result? Sonnet or Haiku may suffice for a straightforward, bounded instruction. Where many dependencies matter, a more extensive approach may save correction work.
Reasoning, knowledge and documents
Opus can analyse relationships in supplied material, compare alternatives and develop a proposal. State which information is established and where estimation is required. Otherwise, a model may fill a missing premise as though it came from the source.
A marketing team might test a positioning proposal against customer interviews, product information and previous campaigns. Request arguments linked directly to those sources. Ask for counterexamples and missing evidence too. This produces a draft people can discuss rather than an apparently definitive judgement.
Opus has knowledge learned during training, but current facts require current sources. Search tools or supplied documents can add that context. More reasoning capability does not automatically refresh old information or turn a convincing statement into an established fact.
Programming and agents
Programming work can involve more than writing one function. A model may need to understand data moving through several modules, reproduce an error and check whether a change affects other components. These are situations in which to evaluate Opus alongside Sonnet.
Through Claude Code or a custom agent, the model can work with a repository, terminal and checks. The environment determines which actions are available. A model without test output cannot demonstrate an executed test. Ask for concrete changes, checks performed and any remaining uncertainty.
Agents can also carry out multi-step work outside programming. An agent could inventory case files, flag missing items and prepare a report draft. A more capable model does not remove the need for clear permissions and a recognisable result.
Current API specifications
The API ID is claude-opus-5-5. Official documentation lists 1 million tokens of context, text and image input, and text output. The relative speed category is “moderate”. Actual response time depends on input, output length, tools and reasoning, among other factors.
Opus 5.5 uses adaptive thinking, which current documentation describes as always enabled. Default effort is medium. Effort is a processing setting within the same model: increasing it does not create another family. Record settings when comparing models so that a configuration difference is not mistaken for a model-quality difference.
The context window is a processing limit, not a guarantee that every detail will be retained. Organise large files and request source locations. Limits in the Claude app, Claude Code and partner platforms need not match the raw model specification.
What might you notice compared with Sonnet?
Suppose an agency is preparing a new service page. Sonnet may suit structure, text alternatives and quick feedback rounds. Opus is a candidate when you must also weigh conflicting customer requirements, technical constraints and several commercial assumptions.
Any difference should appear in the result: fewer missed conditions, better-supported choices or less repair work. A longer response is not inherently useful. Give both models the same sources and acceptance criteria. Measure waiting time and total processing too; official pricing assigns different token rates to different models.
These examples describe a selection method, not a guaranteed ranking. Sonnet can be exactly right for a bounded task. Fable may become relevant when a difficult problem remains inadequately solved despite careful instructions and suitable Opus settings.
History, availability and retired versions
Opus was part of the Claude 3 family in 2024. It developed through several 4.x versions and Opus 5 to Opus 5.5. A family can remain current while older versions have been retired.
The current lifecycle table records Opus 3 as retired on 5 January 2026, Opus 4 on 15 June 2026 and Opus 4.1 on 5 August 2026. Several later 4.x versions and Opus 5 remain active on the review date. When migrating, check your application’s exact model ID and channel.
Opus 5.5 is active in the model catalogue. Access through an app, API or cloud provider follows that account’s and product’s conditions. A Claude subscription and API billing are separate matters. Before purchasing, check that the desired version and usage method are actually included.