Claude Sonnet 5.5 Explained: 30% Faster, a Million-Token Context, $2 per Million Input Tokens and a Coding Score Above Opus 5.5
Anthropic released Claude Sonnet 5.5 on 28 September, and it is still trending as developers compare it with OpenAI's GPT-6.1 Sol. It outputs about 30% faster than Sonnet 5, carries a 1 million token context window, costs $2 per million input tokens and $10 per million output tokens, and scores 70.6% on Terminal-Bench 4.0, above Opus 5.5's 66.4%. What that means in practice.
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Three AI labs shipped or announced flagship-adjacent models in the same ten days, and Anthropic's entry is the one aimed at everyday work. Claude Sonnet 5.5 came out on 28 September and is trending a week later because developers have had time to test it against OpenAI's GPT-6.1 Sol, which shipped three days afterwards. Here is what it is and who it is for.
What Sonnet 5.5 is
Anthropic sells Claude in tiers. Opus is the most capable and most expensive; Sonnet is the mid tier for everyday tasks; Haiku is the small, fast one. Sonnet 5.5 is an upgrade to the mid tier, and its pitch is simple: most of Opus's ability at a fraction of the price and with faster responses.
The numbers
- Speed: about 30 percent faster output than Sonnet 5.
- Context: 1 million tokens, enough to load a large codebase or several books into one conversation.
- Price: $2.00 per million input tokens and $10.00 per million output tokens on the API.
- Coding: 70.6 percent on Terminal-Bench 4.0, a benchmark of agentic terminal tasks, above Opus 5.5's 66.4 percent. Anthropic says Sonnet 5.5 is strongest on well-scoped everyday tasks and bug fixes rather than open-ended research.
- Availability: Claude on the web, iPhone and Android, the Anthropic API, AWS, Google Cloud and Microsoft Foundry. A thinking variant that reasons longer before answering is also offered.
How to read the Opus comparison
Beating Opus on one coding benchmark does not make Sonnet the better model overall; Opus still leads on long, open-ended work. It does mean that for a lot of routine coding, Sonnet is the sensible default, which is exactly what Anthropic wants businesses to conclude when they look at their bills.
Against GPT-6.1 Sol
OpenAI's GPT-6.1 Sol, released 1 October, is the direct rival: a tier below the flagship, pitched at agentic coding and professional work. Early community comparisons are split and depend heavily on the task. The practical difference for most users is which ecosystem they already use.
For users in India
Claude's consumer apps are available in India, and API pricing is in dollars, so the rupee rate matters for developers. At $2 and $10 per million tokens, a typical heavy coding session costs a few rupees to a few tens of rupees.
Frequently asked questions
When was Claude Sonnet 5.5 released?
28 September 2026.
How much does Claude Sonnet 5.5 cost?
$2.00 per million input tokens and $10.00 per million output tokens on the API.
Is Sonnet 5.5 better than Opus 5.5?
It scores higher on Terminal-Bench 4.0 for coding and is faster and cheaper, but Opus remains stronger on long, open-ended tasks.
What is the context window?
1 million tokens.
Where can I use Claude Sonnet 5.5?
In the Claude apps and through the Anthropic API, AWS, Google Cloud and Microsoft Foundry.
