Claude Opus 5.5 vs Claude Sonnet 5.5

As of October 21, 2026, Claude Opus 5.5 costs 100% more per input token than Claude Sonnet 5.5 ($4.00 vs $2.00 per 1M), and both have a 1M-token context window.

Prices from LiteLLM's price fileChecked October 21, 2026

Claude Opus 5.5 vs Claude Sonnet 5.5 side by side

Headline prices in US dollars per 1M tokens: each model's own lab where it sells it, otherwise its cheapest provider. Source: LiteLLM model price file, as of October 21, 2026.
	Claude Opus 5.5	Claude Sonnet 5.5
Input, per 1M tokens	$4.00	$2.00
Output, per 1M tokens	$20.00	$10.00
Cache read, per 1M tokens	$0.20	$0.10
Cache write, per 1M tokens	$5.00	$2.50
Context window	1,000,000 tokens	1,000,000 tokens
Max output	128,000 tokens	128,000 tokens
Image input	Yes	Yes
Tool calling	Yes	Yes
Structured output (JSON)	Yes	Yes
Prompt caching	Yes	Yes
Reasoning	Yes	Yes
Providers on LiteLLM	8	7
Price shown is from	Anthropic	Anthropic
Added to LiteLLM	September 22, 2026	September 28, 2026

Cheapest provider for each

Claude Opus 5.5: Anthropic at $4.00 input and $20.00 output per 1M tokens (claude-opus-5-5)
Claude Sonnet 5.5: Anthropic at $2.00 input and $10.00 output per 1M tokens (claude-sonnet-5-5)

Benchmark scores

From the Epoch AI Benchmarking Hub (CC BY 4.0), data as of September 29, 2026. Some results were run by Epoch and others collected by Epoch from each benchmark's own leaderboard, linked in the first column. Each model's best reported reasoning setting is shown in brackets. Higher is better. Only benchmarks with a score for both models are shown.
Benchmark	Claude Opus 5.5	Claude Sonnet 5.5
Overall
Epoch Capabilities Index	168.8	166.2
Coding and agents
FrontierCode	54.6% (medium)	52.1% (xhigh)
FrontierSWE	62.3% (max)	61.9% (max)
APEX-Agents	73.5% (max)	75.5% (max)
Reasoning and knowledge
GPQA Diamond	90.6% (max)	95.6% (max)
SimpleQA Verified	72.2% (max)	46.5% (max)
Math
FrontierMath (tiers 1-3)	91.2% (max)	88.8% (max)
FrontierMath (tier 4)	95.0% (max)	80.5% (max)
OTIS Mock AIME 2024-2025	100.0% (max)	100.0% (max)

When to pick which

Pick Claude Sonnet 5.5 for

Costs 50% less per input token: $2.00 vs $4.00 per 1M.

From differences in the data above only; where the data is equal, no reason is given.

Call Claude Opus 5.5 or Claude Sonnet 5.5 with LiteLLM

Both use the OpenAI format through LiteLLM, so switching is a model name change. Set each provider's API key in the environment first.

Python SDK

from litellm import completion

messages = [{"role": "user", "content": "Hello!"}]

# Claude Opus 5.5
response = completion(model="claude-opus-5-5", messages=messages)

# Claude Sonnet 5.5
response = completion(model="claude-sonnet-5-5", messages=messages)

# Claude Opus 5.5, falling back to Claude Sonnet 5.5 if the call fails
response = completion(model="claude-opus-5-5", messages=messages, fallbacks=["claude-sonnet-5-5"])

FAQ

Which is cheaper, Claude Opus 5.5 or Claude Sonnet 5.5?

Claude Sonnet 5.5 is cheaper at 3 input tokens per output token: $4.00 per 1M tokens blended ($2.00 input, $10.00 output), versus $8.00 ($4.00 and $20.00) for Claude Opus 5.5, as of October 21, 2026.

Which has the larger context window, Claude Opus 5.5 or Claude Sonnet 5.5?

Both have a 1,000,000-token context window.

Can I switch from Claude Opus 5.5 to Claude Sonnet 5.5 without changing my code?

Yes. Through LiteLLM both use the OpenAI format, so switching means changing the model name from "claude-opus-5-5" to "claude-sonnet-5-5", or pointing a LiteLLM gateway model alias at the other model. You can also use one as a fallback for the other.