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Claude Sonnet 5.5

Anthropic's Sonnet-class model with 1M context and adaptive thinking

Modalities
Image, Text
Text
In / Out price
$2/$10per 1M
Context window
1M tokens
Released
Sep 28, 2026

Overview

The pelican test: one prompt, every text model, unedited SVG output from Nov 3, 2026.

SVG of a pelican riding a bicycle, written by Claude Sonnet 5.5 through AI/ML API

Claude Sonnet 5.5 by Anthropic

Claude Sonnet 5.5 is Anthropic's Sonnet-class model for well-scoped everyday work, succeeding Claude Sonnet 5 as a direct upgrade.

What Claude Sonnet 5.5 Brings to the Table

A large jump in agentic coding
Anthropic reports 70.6% on Terminal-Bench 4.0, against 10.3% for Claude Sonnet 5 on the same evaluation, and 55.5% on CursorBench 4.0 against 34.1%.

Computer use
80.1% on OSWorld 2.1 (partial credit), against 57.0% for Sonnet 5.

Where Claude Sonnet 5.5 Makes the Most Sense

Agentic coding and long-running tasks
The Terminal-Bench and CursorBench gains over Sonnet 5 are the largest Anthropic reports for this release, and they are the tasks the model is aimed at.

Computer-use agents
80.1% on OSWorld 2.1 puts it within two points of Opus 5.5 at a lower price per token.

Claude Sonnet 5.5 vs the Alternatives

Claude Sonnet 5
The model this one replaces. Sonnet 5.5 is ahead on every benchmark Anthropic published for both, by wide margins on the agentic ones.

Claude Opus 5.5
The frontier tier. Opus leads on CursorBench 4.0 (57.8% vs 55.5%) and FrontierCode, ties on GDPval-AA (1846 vs 1844), and trails on Terminal-Bench 4.0 (66.4% vs 70.6%). Sonnet 5.5 is the cheaper choice where that gap does not matter.

Capabilities

  • Reasoning
  • Streaming
  • Function calling
  • Vision

Benchmarks by Artificial Analysis

See how Claude Sonnet 5.5 compares in intelligence, generation speed, cost per task and latency.

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.

Pricing

Claude Sonnet 5.5 pricing in US dollars
UsagePriceUnit
Input$21M tokens
Output$101M tokens
Cached input$0.21M tokens

Compare 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
ModelInputOutput
Claude Sonnet 5.5$2$10
Claude Haiku 5.5$0.1$0.5
Claude Opus 5.5$4$20
Claude Opus 5$5$25
Claude Fable 5.1$10$50

Build with your agent

Give your agent the model details, code and documentation.

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-sonnet-5.5",
  "messages": [
    {
      "role": "user",
      "content": "Write a haiku about the ocean."
    }
  ]
}'

Frequently asked questions

What is Claude Sonnet 5.5 on AI/ML API best for?

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

Does Claude Sonnet 5.5 support reasoning?
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.
Can Claude Sonnet 5.5 use 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.
Does Claude Sonnet 5.5 support vision?
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.
Can Claude Sonnet 5.5 stream responses?
Yes. Response streaming is supported through the standard chat completions endpoint on AI/ML API.
What kinds of tasks fit Claude Sonnet 5.5?

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.

Is Claude Sonnet 5.5 suitable for multi-file coding 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.

Does Claude Sonnet 5.5 work with text and images?
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.
Is Claude Sonnet 5.5 an agentic model?
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.
What should I check before choosing Claude Sonnet 5.5 on AI/ML API?

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

Claude Sonnet 5.5 API

anthropic/claude-sonnet-5.5

Build with your agent

Give your agent the model details, code and documentation.

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-sonnet-5.5",
  "messages": [
    {
      "role": "user",
      "content": "Write a haiku about the ocean."
    }
  ]
}'