Model

Claude Sonnet 5.5

CLOSED

Anthropic · Claude 5.5 family · released Sep 28, 2026

Model id claude-sonnet-5-5, released 2026-09-28 as 'the second model in the Claude 5.5 family'. Anthropic says it runs 30%+ faster than Sonnet 5 and costs up to 30% less per task. List price matches Sonnet 5 at $2/$10. Cache reads launched at $0.20 and were halved to $0.10 on 2026-10-07. It is the first Sonnet to ship with cyber safeguards, which fall back to Sonnet 5. Anthropic says Opus 5.5 is 'clearly stronger at complex, open-ended work' despite similar Max-effort benchmark scores. Its Terminal-Bench 4.0 score (70.6) beats Opus 5.5's (66.4).

ReasoningCodingVisionFunction callingTool useAgentic

3240.8

Elo · rank #3

Parameters

Undisclosed

Active params

—

Context

1M tokens

Architecture

Proprietary model; architecture and parameter count undisclosed; adaptive thinking with a runtime effort parameter, 1M-token context

License

Proprietary

Languages

—

API price (in/out)

$2 / $10

Modalities

text · vision

Benchmark results

Bar shows position within the tracked field; marker = field best

ChartographyVision61.6%#3

best: Gemini 4 Argon · 71.6%

CursorBench 4.0Coding55.5%#2

best: Claude Opus 5.5 · 57.8%

FrontierCodeCoding52.1%#5

best: Claude Opus 5.5 · 54.6%

Humanity's Last ExamReasoning64.5%#3

best: Claude Opus 5.5 · 67.7%

Terminal-Bench 4.0Agents70.6%#1

best: this model · 70.6%

Run it locally

Closed weights — available via API only. No local deployment.

Input / M tok

Output / M tok

$10

Claude 5.5 family

Elo progression across releases

Claude Opus 5.5Sep 20263266.5 Claude Sonnet 5.5Sep 20263240.8 Claude Haiku 5.5Oct 20262922.0

Resources

DOCShttps://platform.claude.com/docs/en/models/sonnet-5-5/overview APIAvailable via Anthropic API

API price $2/$10 · each benchmark row carries its own source badge (see methodology)