# Claude Sonnet 5.5

> Claude Sonnet 5.5 is Anthropic's newest Sonnet, released on September 28, 2026 as the successor to Claude Sonnet 5. Anthropic describes it as the best combination of speed and intelligence in its current lineup, and prices it exactly the same as Sonnet 5. It takes a 1M-token context window and vision input, with adaptive thinking on by default and a default reasoning effort of "high."

Canonical: https://routemux.com/anthropic/claude-sonnet-5-5
Provider: Anthropic

## Key facts

| Field | Value |
| --- | --- |
| Model ID | anthropic/claude-sonnet-5-5 |
| Official model ID | claude-sonnet-5-5 |
| Context window | 1M |
| Max output | 8K |
| Input modalities | text, image |
| Output modalities | text |
| Capabilities | Vision, Reasoning, Tool Calling, Coding, Cache, Paid Cache Write |
| Upstream release | 2026-09-28 |
| Availability | available |

## Pricing

- RouteMux input: $0.56 per 1M tokens
- RouteMux output: $2.8 per 1M tokens
- Official input: $2 per 1M tokens
- Official output: $10 per 1M tokens
- Cache read: $0.056 per 1M tokens
- Cache write: $0.7 per 1M tokens
- Saving vs official: 72%
- Official price source: anthropic_x0.28, verified 2026-09-29

Billing is prepaid wallet, charged per successful request only.

## API access

Base URL: https://api.routemux.com

Supported protocols:

- anthropic_messages

## What is Claude Sonnet 5.5

Claude Sonnet 5.5 is Anthropic's newest Sonnet, released on September 28, 2026 as the successor to Claude Sonnet 5. Anthropic describes it as the best combination of speed and intelligence in its current lineup, and prices it exactly the same as Sonnet 5. It takes a 1M-token context window and vision input, with adaptive thinking on by default and a default reasoning effort of "high."

Through RouteMux it costs $0.56 per 1M input tokens against Anthropic's $2, and $2.80 per 1M output against $10 — the same model and the same Anthropic Messages API, routed through one key alongside every other model in the catalog. Failed and timed-out requests are not billed. Prompt caching is priced separately: reads are $0.056 per 1M tokens, and writes are $0.70 (5-minute) or $1.12 (1-hour) per 1M tokens.

Moving over from Sonnet 5 is mostly a model-name change, but Anthropic lists a few request shapes that now return an error. They are covered in the FAQ below.

## Key capabilities

- **Same price as Sonnet 5** — Anthropic kept Sonnet 5's pricing for the new model: $0.56 / 1M input and $2.80 / 1M output through RouteMux.
- **1M-token context** — Enough to hold a mid-sized repository or a full document set in a single request.
- **Adaptive thinking, steered by effort** — Thinking is on by default at high effort. Anthropic suggests medium for well-specified agentic tasks and medium or low for chat and latency-sensitive work.
- **Vision input and tool calling** — Accepts images alongside text and supports native function calling, so screenshots, diagrams and tool results go in the same conversation.

## Other variants in this family

- Claude Sonnet 5 (`anthropic/claude-sonnet-5`)
- Claude Sonnet 4.6 (`anthropic/claude-sonnet-4.6`)

## Sources

- [Anthropic — Claude Sonnet 5.5](https://platform.claude.com/docs/en/models/sonnet-5-5/overview)
- [Anthropic — What's new in Claude Sonnet 5.5](https://platform.claude.com/docs/en/models/sonnet-5-5/whats-new-sonnet-5-5)
- [Anthropic — Pricing](https://platform.claude.com/docs/en/about-claude/pricing)

_Content reviewed by Jerry Fan on 2026-09-29._