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Anthropic · Frontier

Claude Sonnet 5.5 Thinking

Added Sep 28, 2026

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Use in the app

Claude Sonnet 5.5 with adaptive thinking for complex coding, multi-step tool use, visual analysis, and detailed planning. Supports a 1M-token context window and five reasoning effort levels, with stronger thinking available when a task needs it.

  • Reasoning
  • Tools
  • Vision
  • Structured output
  • PDF input
Input
Text, Images
Output
Text
Reasoning effort
low · medium · high · xhigh · max
Discovery tier
Frontier

Pricing

USD per 1M tokens
Input
$2.00
Output
$10.00
Cache read
$0.10
Cache write
$2.50
$4.00 for a 1-hour cache

Reference prices as published by the model provider. API example

Specifications

Context window
1M
Max output
128K
Average output (7 days)
3K tokens
Longer than 96% of 473 models

Side by side

Claude Sonnet 5.5 Thinking compared

Specifications, prices, speed and benchmark scores next to each other. Benchmarks below show every compared model too.

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Claude Sonnet 5.5 ThinkingAnthropicThis modelClaude Sonnet 4.6AnthropicRemove
ProviderAnthropicAnthropic
Discovery tierFrontierFrontier
AddedSep 28, 2026Feb 17, 2026
Limits
Context window1M1M
Max output128K128K
Average output3K tokens401 tokens
Pricing, USD per 1M tokens
Input$2.00Best$3.00
Output$10.00Best$15.00
Cache read$0.10Best$0.30
Cache write$2.50—
Performance
Throughput203.8 tok/sBest52.4 tok/s
Time to first token6.6 s1.7 sBest
Request success (24h)99.1%99.5%Best
Benchmark indexes
Intelligence Index46.8Best24.7
Capabilities
ReasoningYesYes
ToolsYesYes
VisionYesYes
Structured outputYesYes
PDF inputYesYes
Reasoning effortlow, medium, high, xhigh, maxlow, medium, high, xhigh, max

Public evaluations

Benchmarks

Independent evaluation results, with how each score ranks among the models in the Noumen catalog.

  • Claude Sonnet 5.5 Thinking
  • Claude Sonnet 4.6

Intelligence Index

  • Claude Sonnet 5.5 Thinking46.8
  • Claude Sonnet 4.624.7

Claude Sonnet 5.5 Thinking tested at high reasoning effort

Claude Sonnet 5.5 Thinking: Better than 93% of 326 scored models

3.8Catalog models by score55.1

Agentic work

  • AutomationBench-AA

    Workflow automation, penalized for guardrail violations

    • Claude Sonnet 5.5 Thinking: 59.4%
    • Claude Sonnet 4.6: —

  • AutomationBench-AA tasks completed

    Workflows finished end to end without a guardrail violation

    • Claude Sonnet 5.5 Thinking: 29.4%
    • Claude Sonnet 4.6: —

  • AA-Briefcasev1.1

    Agentic knowledge work, rated head to head

    • Claude Sonnet 5.5 Thinking: 1,635 Elo
    • Claude Sonnet 4.6: —

  • GDPval-AAv2.1

    Economically valuable occupational tasks, rated head to head

    • Claude Sonnet 5.5 Thinking: 1,548 Elo
    • Claude Sonnet 4.6: —

Document reasoning

  • GDP.pdf

    Professional reasoning over PDF documents, all-pass rate

    • Claude Sonnet 5.5 Thinking: 25.2%
    • Claude Sonnet 4.6: —

  • AA-LCRv1.1

    Reasoning across long documents

    • Claude Sonnet 5.5 Thinking: 78.0%Top
    • Claude Sonnet 4.6: 68.3%

  • MLCR-AA

    Long-context reasoning over medical records

    • Claude Sonnet 5.5 Thinking: 18.9%
    • Claude Sonnet 4.6: —

Reasoning and knowledge

  • Humanity’s Last Exam

    Expert-level questions across academic fields

    • Claude Sonnet 5.5 Thinking: 45.8%Top
    • Claude Sonnet 4.6: 13.3%

  • GPQA Diamond

    Graduate-level science questions

    • Claude Sonnet 5.5 Thinking: —
    • Claude Sonnet 4.6: 79.9%

  • IFBench

    Following precise output instructions

    • Claude Sonnet 5.5 Thinking: —
    • Claude Sonnet 4.6: 41.2%

Coding

  • Terminal-Benchv4.0

    Practical software engineering in a terminal

    • Claude Sonnet 5.5 Thinking: 43.9%
    • Claude Sonnet 4.6: —

  • SciCode

    Scientific computing in Python

    • Claude Sonnet 5.5 Thinking: 53.7%
    • Claude Sonnet 4.6: —

Legacy evaluations

  • Terminal-Bench Hard

    Earlier terminal task suite

    • Claude Sonnet 5.5 Thinking: —
    • Claude Sonnet 4.6: 46.2%

  • τ²-Bench Telecom

    Tool use in a customer-support simulation

    • Claude Sonnet 5.5 Thinking: —
    • Claude Sonnet 4.6: 79.5%

  • AA-LCR (unversioned)

    Long-context reasoning, earlier grading

    • Claude Sonnet 5.5 Thinking: 78.0%Top
    • Claude Sonnet 4.6: 68.3%

Scores from Artificial Analysis, updated Oct 26, 2026. Claude Sonnet 5.5 Thinking was tested at high reasoning effort; compare scores measured at the same effort.Artificial Analysis

Live routing data

Performance and reliability

Recent averages across requests routed for this model. Your own speed depends on prompt length, reasoning effort and load.

Throughput
203.8 tok/s
Faster than 85% of 260 models
Time to first token
6.6 s
Quicker than 20% of 260 models
Prompt cache hits
52.9%
About $0.99 per 1M input tokens with caching
Request success (24h)
99.1%
Reliable

Cache hits are the share of input tokens recently served from a prompt cache across all requests. They are not a forecast of your own hit rate.

Hourly request success · last 72 hoursLowest hour 96.9%
  • Healthy (98% or more)
  • Degraded (90–98%)
  • Down (under 90%)
  • No requests

Developers

Use it through the API

Noumen’s API is OpenAI-compatible: any Chat Completions client works with a base URL and a key.

Read the quickstart
curl https://www.noumen.xyz/api/v1/chat/completions \
  -H "Authorization: Bearer $NOUMEN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "anthropic/claude-sonnet-5.5:thinking",
    "reasoning_effort": "medium",
    "messages": [{ "role": "user", "content": "Explain this stack trace." }]
  }'
import os
from openai import OpenAI

client = OpenAI(base_url="https://www.noumen.xyz/api/v1", api_key=os.environ["NOUMEN_API_KEY"])
reply = client.chat.completions.create(
    model="anthropic/claude-sonnet-5.5:thinking",
    messages=[{"role": "user", "content": "Explain this stack trace."}],
)
print(reply.choices[0].message.content)

Anthropic

Other Anthropic models, starting with the same family.