Claude Opus 5.5 API

Q: What is the Claude Opus 5.5 model ID?

Use anthropic/claude-opus-5.5 as the model parameter. Requests go to the OpenAI-compatible endpoint with your AI/ML API key.

Try this model

Anthropic's flagship model for demanding reasoning, coding and long-horizon agentic work, with a 1M token context window and always-on adaptive thinking.

Modalities: TextText
In / Out price: $4/$20per 1M
Context window: 1M tokens
Released: Sep 21, 2026

Claude Opus 5.5 overview

Claude Opus 5.5 specs

Model ID: anthropic/claude-opus-5.5
Developer: Anthropic
Context window: 1,000,000 tokens
Max output: 128,000 tokens
Input: Text
Output: Text
API: OpenAI-compatible, base URL https://api.aimlapi.com/v1

What Is Claude Opus 5.5?

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.

Technical Reference

Model ID: anthropic/claude-opus-5.5
Release date: 22 September 2026
Endpoint: POST /v1/chat/completions
Context window: 1,000,000 tokens
Thinking: always-on adaptive thinking with configurable effort

Benchmarks

Results published by Anthropic at launch, at max effort unless noted.

Terminal-Bench 4.0: 66.4% (Opus 5: 52.3%, Fable 5.1: 55.8%)
FrontierCode v1.1: 54.4% (Opus 5: 48.0%)
CursorBench 4.0: 57.8% (Opus 5: 46.6%)
GDPval-AA v2.1: 1846 Elo (Opus 5: 1708)
AutomationBench: 40.0% (Opus 5: 26.9%)
Humanity's Last Exam: 67.7% (Opus 5: 63.6%)
OSWorld 2.0: 81.8% (Opus 5: 74.0%)
Chartography: 89.0% (Opus 5: 83.4%)

What Claude Opus 5.5 Brings to the Table

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.

Where Claude Opus 5.5 Makes the Most Sense

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

Use cases

Agentic coding: long-running sessions that plan, edit and verify code across many steps
Enterprise knowledge work: analysis, reports and document workflows at scale
Complex reasoning: multi-step problems where the model decides how deeply to think
Tool-using agents: pipelines that call functions and external tools autonomously
Long-context tasks: whole repositories and large document sets in a single request

Capabilities

Function calling
Streaming
Structured outputs
Reasoning
Web search

Claude Opus 5.5 benchmarks by Artificial Analysis

See how Claude Opus 5.5 compares in intelligence, generation speed and cost per task. Data retrieved Nov 3, 2026.

Intelligence#2 / 5058.4Index v5.0 Speed#116 / 21995.5Output tokens / second Cost per task#44 / 44$10.04USD / benchmark task Humanity's Last Exam#1 / 45861.4%Score

Intelligence

Index v5.0

Speed

Output tokens / second

Cost per task

USD / benchmark task

Benchmark results

Compare 5 models available on AI/ML API across 4 independent benchmarks.

Humanity's Last Exam

Expert-written questions across academic subjects.

Claude Opus 5.5 API pricing

Claude Opus 5.5 pricing in US dollars
Usage	Price	Unit
Input	$4	1M tokens
Output	$20	1M tokens
Cached input	$0.2	1M tokens

Prices from the AI/ML API price list, checked on Nov 4, 2026.

Claude Opus 5.5 vs other models: token prices

AI/ML API input and output rates for 5 models, per million tokens.

AI/ML API model prices in USD per million tokens
Model	Input	Output
Claude Opus 5.5	$4	$20
Claude Haiku 5.5	$0.1	$0.5
Claude Sonnet 5.5	$2	$10
Claude Opus 5	$5	$25
Claude Fable 5.1	$10	$50

How to use the Claude Opus 5.5 API

View docs

Build with your agent

Give your agent the model details, code and documentation.

1Get your API key

Create API key

export AIMLAPI_KEY="8f2b4c7d9a1e6b3f…"

2Make your first request

curl '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": "Write a haiku about the ocean."
    }
  ]
}'

import os
import requests

headers = {
    "Authorization": f"Bearer {os.environ['AIMLAPI_KEY']}",
    "Content-Type": "application/json",
}
payload = {
    "model": "anthropic/claude-opus-5.5",
    "messages": [
        {
            "role": "user",
            "content": "Write a haiku about the ocean."
        }
    ]
}

response = requests.post("https://api.aimlapi.com/v1/chat/completions", headers=headers, json=payload, timeout=120)
response.raise_for_status()
print(response.json())

const response = 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": "Write a haiku about the ocean."
      }
    ]
  }),
});

if (!response.ok) throw new Error(`HTTP ${response.status}`);
console.log(await response.json());

Claude Opus 5.5 FAQ

Is Claude Opus 5.5 available on AI/ML API?

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.

When was Claude Opus 5.5 released?

Anthropic released Claude Opus 5.5 on 22 September 2026 as the first model in the Claude 5.5 family.

How much does Claude Opus 5.5 cost?

Claude Opus 5.5 costs $4 input and $20 output per 1M tokens on AI/ML API, billed as you go with no subscription.

How is Claude Opus 5.5 different from Claude Opus 5?

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%.

How do I switch from Claude Opus 5 to Claude Opus 5.5?

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.

What is the Claude Opus 5.5 model ID?

Use anthropic/claude-opus-5.5 as the model parameter. Requests go to the OpenAI-compatible endpoint with your AI/ML API key.

What is the context window of Claude Opus 5.5?

Claude Opus 5.5 accepts up to 1,000,000 tokens of context and returns up to 128,000 output tokens.

Start building with Claude Opus 5.5

Get API key

Claude Opus 5.5 API

anthropic/claude-opus-5.5

Build with your agent

Give your agent the model details, code and documentation.

1Get your API key

Create API key

export AIMLAPI_KEY="8f2b4c7d9a1e6b3f…"

2Make your first request

curl '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": "Write a haiku about the ocean."
    }
  ]
}'

import os
import requests

headers = {
    "Authorization": f"Bearer {os.environ['AIMLAPI_KEY']}",
    "Content-Type": "application/json",
}
payload = {
    "model": "anthropic/claude-opus-5.5",
    "messages": [
        {
            "role": "user",
            "content": "Write a haiku about the ocean."
        }
    ]
}

response = requests.post("https://api.aimlapi.com/v1/chat/completions", headers=headers, json=payload, timeout=120)
response.raise_for_status()
print(response.json())

const response = 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": "Write a haiku about the ocean."
      }
    ]
  }),
});

if (!response.ok) throw new Error(`HTTP ${response.status}`);
console.log(await response.json());

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Claude Opus 5.5 API

Claude Opus 5.5 overview

Claude Opus 5.5 specs

What Is Claude Opus 5.5?

Technical Reference

Benchmarks

What Claude Opus 5.5 Brings to the Table

Where Claude Opus 5.5 Makes the Most Sense

Use cases

Capabilities

Claude Opus 5.5 benchmarks by Artificial Analysis

Intelligence

Speed

Cost per task

Benchmark results

Humanity's Last Exam

Terminal-Bench 4.0

AA-LCR

SciCode

Claude Opus 5.5 API pricing

Claude Opus 5.5 vs other models: token prices

How to use the Claude Opus 5.5 API

Build with your agent

1Get your API key

2Make your first request

Claude Opus 5.5 FAQ

Start building with Claude Opus 5.5

Claude Opus 5.5 API

Build with your agent

1Get your API key

2Make your first request

Claude Opus 5.5 API

Claude Opus 5.5 overview

Claude Opus 5.5 specs

What Is Claude Opus 5.5?

Technical Reference

Benchmarks

What Claude Opus 5.5 Brings to the Table

Where Claude Opus 5.5 Makes the Most Sense

Use cases

Capabilities

Intelligence

Speed

Cost per task

Benchmark results

Humanity's Last Exam

Terminal-Bench 4.0

AA-LCR

SciCode

Claude Opus 5.5 API pricing

Claude Opus 5.5 vs other models: token prices

How to use the Claude Opus 5.5 API

Build with your agent

1Get your API key

2Make your first request

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Start building with Claude Opus 5.5