Claude Opus 5.5 is Anthropic's flagship model for demanding reasoning, coding and long-horizon agentic work, and the first model in the Claude 5.5 family. Released on 22 September 2026, it succeeds Claude Opus 5. Anthropic says it performs at the level of Claude Fable 5.1 on most work while costing about 40% less to run than Opus 5, and generates output more than 30% faster than Opus 5.
Results published by Anthropic at launch, at max effort unless noted.
Fable-level work at Opus cost
Anthropic reports performance at the level of Claude Fable 5.1 on most tasks, with input and output tokens 20% cheaper than Opus 5 and cache reads 60% cheaper.
Agentic coding
The largest gains are on long, complex engineering work: Terminal-Bench 4.0 rises from 52.3% on Opus 5 to 66.4%, and one early tester completed a 680,000-line code migration in under a day.
Faster output
Output is generated more than 30% faster than Opus 5 at the default setting.
Always-on adaptive thinking
The model decides how much to reason on each step; the effort level trades depth against cost.
Agentic coding
Large migrations, refactors and multi-step changes across big codebases.
Enterprise knowledge work
Research, analysis and document-heavy workflows where quality matters most.
Computer use and automation
Long-running agents that operate software and carry context across many steps.
Sources: https://www.anthropic.com/claude-opus-5-5 · https://docs.aimlapi.com/api-references/text-models-llm/anthropic/claude-opus-5.5
Measured on the AI/ML API gateway across live traffic. Figures are medians unless stated. Last updated 2026-10-12.
import requests r = requests.post( "https://api.aimlapi.com/v1/chat/completions", headers={"Authorization": "Bearer " + AIMLAPI_KEY}, json={ "model": "anthropic/claude-opus-5.5", "messages": [ { "role": "user", "content": "Hello!" } ] }, ) print(r.json())
const r = await fetch("https://api.aimlapi.com/v1/chat/completions", { method: "POST", headers: { Authorization: `Bearer ${process.env.AIMLAPI_KEY}`, "Content-Type": "application/json", }, body: JSON.stringify({ "model": "anthropic/claude-opus-5.5", "messages": [ { "role": "user", "content": "Hello!" } ] }), }); console.log(await r.json());
curl -X POST https://api.aimlapi.com/v1/chat/completions \ -H "Authorization: Bearer $AIMLAPI_KEY" \ -H "Content-Type: application/json" \ -d '{"model":"anthropic/claude-opus-5.5","messages":[{"role":"user","content":"Hello!"}]}'
OpenAI-compatible — swap the base URL and it works with your existing SDK.
| Type | Price |
|---|---|
| Input | |
| Output | |
| Cached input |
Cache writes are billed at $6.5 / 1M tokens.
| Benchmark | Score | What it measures | Source | Retrieved |
|---|---|---|---|---|
| Intelligence | 57.6 | Composite score across standardised reasoning, knowledge and problem-solving evaluations, measured independently by Artificial Analysis | Source | September 25, 2026 |
| Model | Input | Output | Context | Best for |
|---|---|---|---|---|
Claude Opus 5.5 This page | Complex agentic coding and enterprise workflows | |||
| Complex agentic coding and enterprise workflows | ||||
| Long-horizon agentic coding and research | ||||
| Chat + assistants | ||||
| Multimodal reasoning |
Yes. Claude Opus 5.5 is available on AI/ML API through the OpenAI-compatible chat completions endpoint under the model ID anthropic/claude-opus-5.5.
Anthropic released Claude Opus 5.5 on 22 September 2026 as the first model in the Claude 5.5 family.
On AI/ML API, Claude Opus 5.5 costs $5.2 per million input tokens, $26 per million output tokens and $0.26 per million cached input tokens. Cache writes are billed at $6.5 per million tokens.
Anthropic reports that Opus 5.5 performs at the level of Claude Fable 5.1 on most work, costs about 40% less to run than Opus 5 and generates output more than 30% faster. The biggest gains are in agentic coding: Terminal-Bench 4.0 goes from 52.3% on Opus 5 to 66.4%, and CursorBench 4.0 from 46.6% to 57.8%.
Change the model ID from anthropic/claude-opus-5 to anthropic/claude-opus-5.5. Both are served through the same chat completions endpoint on AI/ML API, so nothing else in your integration needs to change.
