Claude Sonnet 5.5 API

anthropic/claude-sonnet-5.5
Claude Sonnet 5.5 is Anthropic's Sonnet-class model for well-scoped everyday work, succeeding Claude Sonnet 5 as a direct upgrade.
Context
1M tokens
Input
$2.6 / 1M tokens
Output
$13 / 1M tokens
Released
Sep 28, 2026

How to use Claude Sonnet 5.5 API

Install any OpenAI-compatible SDK, point it at api.aimlapi.com/v1, and set the model to anthropic/claude-sonnet-5.5.
import requests

r = requests.post(
    "https://api.aimlapi.com/v1/chat/completions",
    headers={"Authorization": "Bearer " + AIMLAPI_KEY},
    json={
      "model": "anthropic/claude-sonnet-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-sonnet-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-sonnet-5.5","messages":[{"role":"user","content":"Hello!"}]}'

OpenAI-compatible — swap the base URL and it works with your existing SDK.

Claude Sonnet 5.5 API Pricing

TypePrice
Input
$2.6 / 1M tokens
Output
$13 / 1M tokens
Cached input
$0.26 / 1M tokens

Claude Sonnet 5.5 Benchmarks

BenchmarkScoreWhat it measuresSourceRetrieved
Intelligence
56
Composite score across standardised reasoning, knowledge and problem-solving evaluations, measured independently by Artificial AnalysisSourceSeptember 28, 2026
Terminal-Bench
70.6% (v4.0)
Autonomous shell/terminal task completionSourceSeptember 28, 2026
OSWorld
80.1% (v2.1, partial)
Computer-use across real desktop applicationsSourceSeptember 28, 2026
Humanity's Last Exam
64.5% (with tools)
Expert-level questions across many domainsSourceSeptember 28, 2026

Terminal-Bench, OSWorld and Humanity's Last Exam as published by Anthropic at release. Intelligence Index measured independently by Artificial Analysis.

Claude Sonnet 5.5 vs other models

ModelInputOutputContextBest for
$2.6 / 1M tokens
$13 / 1M tokens
1M tokens
Multimodal reasoning
$5.2 / 1M tokens
$26 / 1M tokens
1M tokens
Complex agentic coding and enterprise workflows
$13 / 1M tokens
$65 / 1M tokens
1M tokens
Long-horizon agentic coding and research
$4.1262 / 1M tokens
$20.631 / 1M tokens
1M tokens
Agentic workflows and structured output

Frequently asked questions

It is built for coding, agents, and professional work at scale. It is also described as suitable for reasoning, streaming, tools, and vision.

Yes. Adaptive thinking is always on for Claude Sonnet 5.5, and reasoning is listed among its capabilities on AI/ML API. Anthropic reports 64.5% on Humanity's Last Exam with tools.
Yes. Tool and function calling are supported. Anthropic reports 70.6% on Terminal-Bench 4.0 and 80.1% on OSWorld 2.1, both of which measure tool and computer use.
Yes. Claude Sonnet 5.5 accepts image input alongside text. Anthropic reports 61.6% on Chartography without tools, and says it is the first Sonnet model to finish Pokemon Red working only from screenshots.
Yes. Response streaming is supported through the standard chat completions endpoint on AI/ML API.

Anthropic positions it for coding, multi-step workflows and autonomous agents, and reports its largest gains over Claude Sonnet 5 on agentic evaluations such as Terminal-Bench 4.0 and CursorBench 4.0. The 1M-token context window also suits long documents and whole-repository work.

Yes. Anthropic says it is designed to navigate real codebases, land multi-file changes, and carry longer debugging and refactoring tasks through to completion.

Yes. It accepts text and image input and returns text, with a 1,000,000-token context window and up to 128,000 output tokens.
Yes. It is built for agentic work, and the largest gains Anthropic reports over Claude Sonnet 5 are on agentic evaluations: 70.6% against 10.3% on Terminal-Bench 4.0, and 55.5% against 34.1% on CursorBench 4.0.

Confirm that your workflow needs coding, agentic automation, tool use, or vision. The model is positioned for professional tasks at scale, so it is a strong fit when those capabilities matter most.

Start building with Claude Sonnet 5.5

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