Claude Opus 5.5 — the everyday model for coding and knowledge work
Claude Opus 5.5 handles long coding sessions, research and documents with a 1M-token context. $1.40 / 1M input, $7.00 / 1M output per 1M tokens.
- Adaptive thinking
- 1M-token context
- Images and PDFs
- Prompt caching
- Streaming
Try Claude Opus 5.5
Chat with Claude Opus 5.5, attach images or PDFs, and see the tokens and cost of every answer.
claude-opus-5-5$1.40 in · $7.00 out per 1M tokensTry one of these prompts
Messages are billed from your balance at the rates below, like an API call. Failed requests are free.
Real Claude Opus 5.5 output
One prompt, sent to Claude Opus 5.5 at low effort. Unedited.
Explain the difference between optimistic and pessimistic locking in a database, in two short paragraphs, and say when to use each.
**Pessimistic locking** assumes conflicts are likely, so it locks a record as soon as a transaction reads it for update (e.g., `SELECT ... FOR UPDATE`). Other transactions that try to modify it must wait until the lock is released. This guarantees no one else can change the data mid-transaction, but it reduces concurrency and can cause blocking or deadlocks. Use it when contention is high, conflicts are costly or hard to retry, or transactions are short and critical, as with bank balance transfers or inventory decrements on hot items. **Optimistic locking** assumes conflicts are rare, so it takes no lock while reading. Instead, it checks at write time whether the data changed since it was read, typically with a version number or timestamp (e.g., `UPDATE ... SET version = version + 1 WHERE id = ? AND version = ?`). If another transaction got there first, the update affects zero rows and the application retries or reports the conflict. This scales well and avoids holding locks during long operations, such as a user editing a form. Use it when reads far outnumber writes, conflicts are infrequent, or work spans long periods where holding a lock would be impractical.
Generated 2026-09-27. Answers vary from run to run.
Claude Opus 5.5 pricing
Claude Opus 5.5 is billed per token from your balance. Rates below are live, the same ones your account is charged.
Example sizes are for illustration. Your bill follows the tokens each request reports.
| Category | Defaultclaude-opus-5-5 | AWSBclaude-opus-5-5:claude-0.7 | Officialclaude-opus-5-5:claude-0.95 |
|---|---|---|---|
| Price · 1M tokens | Price · 1M tokens | Price · 1M tokens | |
| Input | $1.40 | $2.80 | $3.80 |
| Output | $7.00 | $14.00 | $19.00 |
| Cache read | $0.07 | $0.14 | $0.19 |
| Cache write, 5 minutes | $1.75 | $3.50 | $4.75 |
| Cache write, 1 hour | $2.80 | $5.60 | $7.60 |
What is Claude Opus 5.5?
Claude Opus 5.5 is Anthropic's model for long-running agentic coding and knowledge work, and the model Anthropic suggests starting with for most workloads. It reads up to 1M tokens and writes up to 128K per request.
Claude Opus 5.5 always thinks adaptively: you choose the effort, from low to max, and it decides how much reasoning each task needs. The default is medium, a good balance of quality, speed and cost.
Model ID: claude-opus-5-5 · Input: text, images, PDFs · Output: text · Formats: Anthropic Messages, OpenAI Chat Completions, OpenAI Responses.
Two ways to use Claude Opus 5.5
Call it from your code, or let your coding agent do it for you.
Call it from your backend
Point the official Anthropic SDK at SeedRouter and keep your code. Claude Opus 5.5 also answers the OpenAI formats.
- 1Create an API key
- 2Set the base URL to https://api.seedrouter.ai
- 3Send claude-opus-5-5 as the model
Hand it to your coding agent
Copy a ready prompt. Your agent shows the request and cost before anything is spent.
- 1Copy the prompt
- 2Paste it into your agent
- 3Approve the request
What Claude Opus 5.5 is good at
Claude Opus 5.5 is built for long tasks that need care, not just speed.
Long coding sessions
Claude Opus 5.5 keeps a whole codebase in view and works through multi-step changes.
Research and analysis
Feed it reports, papers or transcripts and get grounded summaries and comparisons.
Documents and files
Claude Opus 5.5 reads PDFs, charts and screenshots alongside your text.
Agent workflows
Tool use and a 1M-token context let an agent run for many steps without losing the thread.
Effort you control
Low for quick answers, max for hard problems. Pay for the thinking you ask for.
Cheaper repeat context
Cached prompt reads on Claude Opus 5.5 cost 5% of the input rate.
What teams build with Claude Opus 5.5
Code review bots
Run Claude Opus 5.5 on every pull request and post findings back.
Support assistants
Answer from your docs with the whole knowledge base in context.
Document extraction
Turn contracts and invoices into structured JSON with output_config.format.
Start using Claude Opus 5.5 in four steps
- 01
Create a key
Sign in and create an API key. Add credit whenever you need it; there is no subscription.
- 02
Change the base URL
Point the Anthropic or OpenAI SDK at https://api.seedrouter.ai. Your code stays the same.
- 03
Pick Claude Opus 5.5
Send claude-opus-5-5 as the model. Set effort to trade depth for speed and cost.
- 04
Check the bill
Every request shows its tokens and charge in your usage records.
Claude Opus 5.5 on SeedRouter at a glance
What you can use today.
- Anthropic Messages API
- Yes, official format
- OpenAI Chat Completions
- Yes
- OpenAI Responses
- Yes
- Image and PDF input
- Yes, by URL or base64
- Prompt caching
- 5-minute and 1-hour
- Forced tool use
- No, per the official model notes
- Failed requests
- Not charged
Batch processing and fast mode are not offered.
Claude Opus 5.5 limits
1M-token context
On Claude Opus 5.5, prompt, files and history share one 1M-token window.
128K tokens out
One Claude Opus 5.5 request can return up to 128K tokens, thinking included.
Thinking stays on
Adaptive thinking cannot be turned off. Lower the effort to make it think less.
Sampling settings
Claude Opus 5.5 follows the official notes on temperature, top_p and top_k; test before relying on them.
Why call Claude Opus 5.5 through SeedRouter
One key, three formats
Call Claude Opus 5.5 with Anthropic Messages, OpenAI Chat Completions or Responses, all with the same key.
Pay per token
Top up once and spend it on any model. No plan, no monthly fee.
Failures are free
A request that errors is not charged.
Live prices
The rates on this page are the rates your account pays.
Prompt caching
Mark long, reused context and later Claude Opus 5.5 requests read it at the cache rate.
Images and PDFs
Send charts, screenshots and documents with your prompt.
Streaming
Stream Claude Opus 5.5 tokens as they arrive with stream: true.
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View pricingClaude Opus 5.5 guides
Walkthroughs and comparisons for this model.
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Call the Claude Fable 5.1 API: get an API key, use the claude-fable-5-1 model ID, send a first request in Python or Node.js, and switch to Opus 5.5.
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Claude Opus 5.5 FAQ
What is Claude Opus 5.5?+
Claude Opus 5.5 is Anthropic's model for long-running agentic coding and knowledge work, released September 22, 2026. It has a 1M-token context window, writes up to 128K tokens per request and thinks adaptively.
Is Claude Opus 5.5 better than Claude Fable 5.1 or Claude Opus 5?+
Anthropic suggests starting with Claude Opus 5.5 for most workloads and moving to Claude Fable 5.1 when a task needs deeper reasoning. Claude Opus 5 is now a legacy model; Claude Opus 5.5 is the current Opus.
Is Claude Opus 5.5 cheaper than Claude Fable 5.1?+
Yes. Claude Opus 5.5 is billed at $1.40 / 1M input and $7.00 / 1M output per 1M tokens, less than Claude Fable 5.1, and its cached reads cost 5% of the input rate.
What is the default effort of Claude Opus 5.5?+
Claude Opus 5.5 defaults to medium effort. You can set low, medium, high, xhigh or max; thinking cannot be turned off, only turned down.
When was Claude Opus 5.5 released and what is its knowledge cutoff?+
Anthropic released Claude Opus 5.5 on September 22, 2026, with a reliable knowledge cutoff of June 2026. Anthropic will not retire it before September 22, 2027.
What is the Claude Opus 5.5 model ID and how do I call it?+
The model ID is claude-opus-5-5. Create a SeedRouter API key, point the Anthropic SDK at https://api.seedrouter.ai and send claude-opus-5-5 as the model; the request and response keep the official Messages format.
Does Claude Opus 5.5 work with the OpenAI SDK?+
Yes. Claude Opus 5.5 also answers the OpenAI Chat Completions and Responses formats at https://api.seedrouter.ai/v1, with the same key and the model ID claude-opus-5-5.
Am I charged if a Claude Opus 5.5 request fails?+
No. A Claude Opus 5.5 request that returns an error is not charged. You pay only for the tokens a finished request reports.
Try Claude Opus 5.5 now
Send your first Claude Opus 5.5 request from the playground or your own code in minutes.