Anthropic launched Claude Opus 5.5 on September 22, 2026, introducing the first model in its Claude 5.5 family. The release focuses on complex coding, long-running AI tasks and professional work, while reducing the cost of running the model compared with its predecessor.
For developers, one of the most interesting questions is what Opus 5.5 changes inside Claude Code, Anthropic’s AI coding tool. A model that can understand a large codebase, follow a multi-step plan and make coordinated changes may be useful for projects that extend well beyond generating a single function.
Here is what Anthropic has announced, how to access Opus 5.5 in Claude Code and what to consider before using it on a real project.
Read Anthropic’s official Claude Opus 5.5 announcement
What Is Claude Opus 5.5?
Claude Opus 5.5 is an AI model designed for demanding tasks, including software development, research and workflows that involve multiple steps or tools.
Anthropic describes it as the first release in the Claude 5.5 family. According to the company, Opus 5.5 delivers performance comparable to Claude Fable 5.1 on many tasks while costing less to run than the earlier Opus 5 model.
Those comparisons come from Anthropic’s published evaluations and early-user testing. Results on an individual project will still depend on the task, the instructions, the available tools and how success is measured.
For people who use AI during development, the practical question is whether Opus 5.5 can help them complete larger pieces of work with fewer revisions.
What’s New in Claude Opus 5.5?
1. A Focus on Longer Coding Tasks
Opus 5.5 is designed for work that may require an AI assistant to inspect several files, understand dependencies, propose changes and continue working through a sequence of steps.
That makes it relevant to projects such as application updates, codebase reviews and migrations between frameworks or programming languages.
Anthropic reports that, during early testing, one user completed a migration involving 680,000 lines of code in less than a day. This is a reported example from an early tester, not a promise that every migration can be completed at the same speed.
For everyday development, a more useful test may be to give Opus 5.5 a well-defined task in an existing repository and assess whether its changes are correct, maintainable and consistent with the project.
2. A Large Context Window
According to Anthropic’s model documentation, Claude Opus 5.5 has a 1 million-token context window and supports up to 128,000 output tokens in its standard API configuration.
A large context window can help when a task involves extensive documentation, several related files or a long conversation about an ongoing project.
However, a large context window does not mean that every file in a repository should automatically be included in a prompt. Providing the most relevant files, clear instructions and a specific goal can still make a workflow easier to manage.
Explore the Claude Opus 5.5 model specifications
3. Faster Output and Lower Running Costs
Anthropic says Opus 5.5 generates output more than 30% faster than Opus 5 in its testing.
The company also reports that typical workloads at default settings can cost approximately 40% less to run than with Opus 5. This overall estimate reflects both pricing changes and the number of tokens used to complete a task.
The actual time and cost savings for an individual workflow may differ. A complex repository update, for example, can require repeated tool calls, tests and reviews regardless of which model is selected.
4. Changes to Reasoning and Communication
Opus 5.5 uses adaptive thinking, which is always enabled. Developers can control the model’s thinking depth through its supported effort settings, but they cannot switch thinking off for this model.
Anthropic also says it has worked on making the model’s responses clearer and more natural. This may be useful during extended development sessions, when an AI assistant needs to explain what it changed and why.
For API users migrating from earlier models, the always-on thinking behaviour is an important compatibility detail. Existing integrations should be checked against Anthropic’s migration documentation before switching model IDs.
Read Anthropic’s Opus 5.5 migration guidance
What Does Claude Opus 5.5 Mean for Claude Code?
Claude Code is Anthropic’s coding tool for working with projects through a terminal and other supported development environments.
Instead of only asking an AI model to produce a code snippet, a developer can use Claude Code to inspect an existing project, discuss an implementation plan and carry out permitted development tasks.
Opus 5.5 gives Claude Code users another model to test for work such as:
- Investigating a problem that involves several connected files.
- Updating an application while preserving existing behaviour.
- Refactoring code and checking whether tests still pass.
- Reviewing a repository before planning a larger change.
- Working through a multi-step feature request with developer oversight.
The model may be capable of completing several actions in sequence, but the developer remains responsible for reviewing changes, especially when a task affects production systems, user data or important business functions.
A Practical Example: Improving a Website
Imagine you maintain a content website and notice that article images are being cropped incorrectly on mobile devices.
You could ask Claude Code to inspect the components responsible for article images, identify where the image sizing rules are applied and propose a change that allows an image to be displayed in full.
A useful instruction would describe the desired result: preserve the image’s aspect ratio, avoid cutting off important content and maintain a clean layout across desktop and mobile screens.
After Claude Code proposes or applies a solution, you would still preview the affected pages, check other image formats and confirm that the change does not introduce layout problems elsewhere.
This illustrates where an AI coding assistant can fit into development: understanding the existing implementation, making a targeted change and helping you verify the result.
How to Use Claude Opus 5.5 in Claude Code
If you already use Claude Code and have access to Opus 5.5, you can select the model from the tool’s model menu.
Open Claude Code in your terminal:
claudeThen enter:
/modelChoose Opus 5.5 from the available models. To check which model your session is currently using, enter:
/statusAnthropic’s model configuration guide lists claude-opus-5-5 as the model identifier and explains additional ways to configure a preferred model.
If Opus 5.5 does not appear in your model menu, check your Claude Code version, account access and the model options available to your subscription or organisation.
Read the Claude Code model configuration guide
Claude Opus 5.5 Availability
Anthropic says Opus 5.5 is available in Claude for Pro, Max, Team and Enterprise users, subject to the applicable product access and usage limits.
Developers can also access the model through the Claude API using the identifier:
claude-opus-5-5Anthropic lists availability through additional cloud platforms, including Amazon Web Services, Google Cloud and Microsoft Azure.
If you use Claude Code through a subscription, check your plan’s current usage allowances. If you use it through API billing, usage is charged according to the applicable API rates and any additional services involved in your workflow.
How Much Does Claude Opus 5.5 Cost?
Anthropic’s published standard API rates for Opus 5.5 are:
Claude Opus 5.5 API Pricing
- Input tokens: $4 per 1 million tokens.
- Output tokens: $20 per 1 million tokens.
- Cache reads: $0.20 per 1 million tokens.
For comparison, Anthropic listed Opus 5 at $5 per million input tokens and $25 per million output tokens. That means Opus 5.5’s standard input and output token prices are 20% lower than those of Opus 5.
Anthropic’s broader estimate of approximately 40% lower cost for typical workloads also takes token efficiency into account; it is not a flat 40% reduction in every published token rate.
What About Fast Mode?
Anthropic also offers a Fast mode for Opus 5.5 in Claude Code and on the Claude Platform.
The company says this mode can run at up to 2.5 times the standard speed. Its published API rates are $8 per million input tokens and $40 per million output tokens.
Fast mode may be useful when faster responses are especially valuable, but its pricing differs from standard mode. Check the cost and availability shown in your product before enabling it.
API token prices are not the same as Claude subscription fees. The amount you pay depends on how you access the model and how much usage your workflow requires.
Check Anthropic’s current model documentation and pricing
Should You Use Opus 5.5 for Every Coding Task?
Not every development task requires the same model or the same amount of reasoning.
For a short explanation or a small, well-defined code change, you may find that another available model meets your needs. For a project involving multiple files, dependencies and several rounds of verification, testing Opus 5.5 may be worthwhile.
A practical comparison is to give your existing model and Opus 5.5 the same representative task, then review:
- Whether the proposed code works as intended.
- How many changes or corrections were needed.
- Whether the model followed the project’s existing conventions.
- How long the task took to complete.
- The total usage or API cost, where applicable.
This approach helps you choose a model based on its performance in your own development environment, rather than relying on a benchmark result alone.
Frequently Asked Questions
When Was Claude Opus 5.5 Released?
Anthropic announced Claude Opus 5.5 on September 22, 2026, as the first model in its Claude 5.5 family.
Is Claude Opus 5.5 Available in Claude Code?
Yes. Anthropic lists Opus 5.5 as a supported Claude Code model. Availability in an individual session depends on the account, subscription or API configuration being used.
How Do I Select Opus 5.5 in Claude Code?
Start Claude Code, enter /model and select Opus 5.5 if it appears in the available options. Use /status to check the current model.
What Is the Claude Opus 5.5 API Model ID?
The API model identifier is claude-opus-5-5.
Can Opus 5.5 Work with Large Codebases?
Its 1 million-token context window and focus on long-running coding tasks make it relevant to projects with substantial context. Results still depend on how the task is scoped, which files and tools are available, and how the changes are reviewed.
Does Opus 5.5 Replace Human Code Review?
No. AI-generated code should be tested and reviewed before being merged or deployed. This is particularly important for changes involving authentication, payments, personal information or production infrastructure.
Final Thoughts
Claude Opus 5.5 brings together a large context window, updated reasoning behaviour and a focus on longer coding and professional workflows. Anthropic also reports improved output speed and lower typical running costs compared with Opus 5.
For Claude Code users, the release creates an opportunity to test the model on more substantial development tasks: investigating issues across files, preparing codebase updates and carrying work through several stages.
The most useful next step is to try Opus 5.5 on a real but manageable project, review the changes carefully and compare the results with your current workflow.
