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How smart is Claude Sonnet 5.5?

140 SI-IQ · 90% interval 137–143
Rank 4 of 80 ranked models · Plausible rank range 3–11

Claude Sonnet 5.5 is a model from Anthropic, released on Sep 28, 2026. Its SI-IQ is 140 (90% interval 137–143), estimated from 8 benchmark results by 2 independent evaluators. Its strongest area is Reasoning and its weakest is Knowledge.

Facts

Developer: Anthropic
Released: Sep 28, 2026
Access: API access
Benchmarks used: 8 results from 2 evaluators
API price: $2.00 input / $10 output per 1M tokens (developer's price list, Oct 18, 2026)
Context window: 1,000,000 tokens

Ability by area (SI-IQ, 90% interval)

Every benchmark result we used

Each score is one value exactly as the source published it: for Epoch AI the best of its run settings, for OpenRouter the median hosting provider (the developer's own hosting when it ran the test). “Implied SI-IQ” is the ability that this single result points to; the overall SI-IQ is their precision-weighted average.

Benchmark	Area	Score	Implied SI-IQ	Evaluated by	As listed by the source	Retrieved	Source
Chess Puzzles	Reasoning	59.0%	139	Epoch AI	`claude-sonnet-5-5_max`	Oct 18, 2026	Epoch AI Benchmarking Hub · data file
Furniture Assembly not in index	Reasoning	75.0%	—	Epoch AI	`claude-sonnet-5-5_max`	Oct 18, 2026	Epoch AI Benchmarking Hub · data file
Mystery Game Puzzles	Reasoning	65.0%	146	Epoch AI	`claude-sonnet-5-5_max`	Oct 18, 2026	Epoch AI Benchmarking Hub · data file
FrontierMath Tier 4	Math	80.5%	140	Epoch AI	`claude-sonnet-5-5_max`	Oct 18, 2026	Epoch AI Benchmarking Hub · data file
FrontierMath Tiers 1–3	Math	88.8%	140	Epoch AI	`claude-sonnet-5-5_max`	Oct 18, 2026	Epoch AI Benchmarking Hub · data file
OTIS Mock AIME 2024–2025	Math	100.0%	142	Epoch AI	`claude-sonnet-5-5_max`	Oct 18, 2026	Epoch AI Benchmarking Hub · data file
GPQA Diamond	Knowledge	95.6%	142	Epoch AI	`claude-sonnet-5-5_max`	Oct 18, 2026	Epoch AI Benchmarking Hub · data file
GPQA Diamond (OpenRouter run)	Knowledge	92.9%	138	OpenRouter	`anthropic/claude-sonnet-5.5-20260928` Anthropic · first-party provider (1 of 5 rows)	Oct 18, 2026	OpenRouter benchmark datasets · data file
SimpleQA Verified	Knowledge	46.5%	126	Epoch AI	`claude-sonnet-5-5_max`	Oct 18, 2026	Epoch AI Benchmarking Hub · data file
τ²-bench Airline (OpenRouter run)	Agents	77.5%	134	OpenRouter	`anthropic/claude-sonnet-5.5-20260928` Anthropic · first-party provider (1 of 5 rows)	Oct 18, 2026	OpenRouter benchmark datasets · data file

Models with similar SI-IQ

Model	SI-IQ
GPT-6 SolOpenAI	140	Claude Sonnet 5.5 vs GPT-6 Sol
Gemini 4 ArgonGoogle DeepMind	140	Claude Sonnet 5.5 vs Gemini 4 Argon
GPT-5.6 SolOpenAI	140	Claude Sonnet 5.5 vs GPT-5.6 Sol
Claude Fable 5.1Anthropic	140	Claude Sonnet 5.5 vs Claude Fable 5.1
GPT-5.5OpenAI	138	Claude Sonnet 5.5 vs GPT-5.5

Computed with SI-IQ method version 1.0.0. Read the full methodology

Data sources: Epoch AI, ‘Capabilities & benchmarking’ (CC BY 4.0); API list prices via LiteLLM's price table (MIT); each price links to the developer's pricing page; Source: OpenRouter (openrouter.ai), licensed under CC BY 4.0.