Anthropic · Released September 28, 2026
Claude Sonnet 5.5
Anthropic's most capable generally available Sonnet (September 28, 2026) — flagship-level performance at $2/$10 per million API tokens.
Best for: people deciding whether this model's paid plan is worth it — and looking for the free way into the same family.
What it costs
API at $2 per million input and $10 per million output tokens; included in Claude Pro.
What it is
Claude Sonnet 5.5, released September 28, 2026, is Anthropic's most capable generally available model in the Sonnet family — described by the company as flagship-grade performance in the workhorse tier. At $2 per million input and $10 per million output tokens, it matches the API pricing Google set for Gemini 4 Argon, which has become the going rate for frontier-tier capability.
In practice Sonnet is the model most Claude developers build on: strong coding and reasoning, fast enough for production loops, and materially cheaper than the Opus tier. Reuters covered its release as Anthropic's second 5.5-model rollout in a week, ahead of the smaller Haiku 5.5 in October.
For developers who want to try the Sonnet line without a bill, Anthropic's free tier at claude.ai and the free allowances on third-party gateways like OpenRouter are the realistic starting points.
The free way into this family
claude.ai's free tier covers the Claude family daily, and OpenRouter's free-tier models are a zero-cost way for developers to test the Sonnet line before paying per token.
Free Anthropic tools, hand-checked
Genuinely free listings from the same ecosystem — each verified against the provider's own pages:
Claude
Anthropic · Claude Sonnet 5
Anthropic's AI assistant for writing, research, and analysis — free to start at claude.ai, with paid Pro and Max plans for heavier use.
OpenRouter
OpenRouter
A single API and dashboard that routes requests to hundreds of AI models from many providers — OpenAI-compatible, pay-as-you-go with no subscription, and with a selection of free models, at openrouter.ai.