How much does the Claude Sonnet 5.5 API cost?

On FastMetal, Claude Sonnet 5.5 is billed per token in yen: ¥357.4 per 1M input tokens and ¥1,787 per 1M output tokens, before tax. Usage is drawn from a prepaid balance; there is no subscription or monthly fee.

Can I call Claude Sonnet 5.5 with the OpenAI SDK?

Yes. Point base_url at https://api.fastmetal.ai/v1 and pass "anthropic-claude-sonnet-5-5" as the model; existing OpenAI-style code works unchanged, including streaming, tool calls and structured output.

What is the context window of Claude Sonnet 5.5?

1,000,000 tokens, shared between the prompt and the response.

What do I need to try Claude Sonnet 5.5?

Create an account and add credit; the model is then available both in the browser chat and over the API. There is no contract or minimum spend.

Back to Models

anthropic-claude-sonnet-5-5

Claude Sonnet 5.5

Claude Sonnet 5.5 is Anthropic's Sonnet-class model for well-scoped everyday work, succeeding Claude Sonnet 5 as a direct upgrade. It is especially strong at building features, fixing bugs, and producing...

9/28/2026

1,000,000 tokens

Input: ¥357.4/M

Output: ¥1,787/M

Try in Chat Get API Key

Specifications

Modalities

Input

text

image

file

Output

text

Supported Parameters

include_reasoning

max_completion_tokens

max_tokens

reasoning

reasoning_effort

response_format

stop

structured_outputs

temperature

tool_choice

tools

verbosity

Max Output Tokens

128,000

Reasoning Configuration

Default: Thinking on (effort: high)
Selectable effort levels: max
xhigh
high
medium
low
Turning thinking off: Not possible (always thinks)

How to control thinking, and what it costs

Data policy

Prompt retention: Unknown — we could not confirm
Training: Not used for training

"Unknown" does not mean "safe". It means we could not confirm it.

Whether a provider trains on prompts is a declared value from our terms with them. Retention is determined from the upstream listing for every host this model can reach. Neither is guessed.

Code Examples

curl https://api.fastmetal.ai/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "anthropic-claude-sonnet-5-5",
    "messages": [{"role": "user", "content": "Hello!"}]
  }'

How Claude Sonnet 5.5 actually answers

Real responses to our standard prompts, recorded on FastMetal.

Count the number of 'r's in 'strawberry'

Count the number of 'r's in 'strawberry'. Explain your reasoning step by step.

Let me go through the word letter by letter. **strawberry** | Position | Letter | |---|---| | 1 | s | | 2 | t | | 3 | **r** ← 1st | | 4 | a | | 5 | w | | 6 | b | | 7 | e | | 8 | **r** ← 2nd | | 9 | **r** ← 3rd | | 10 | y | **Step-by-step reasoning:** 1. I split the word into individual letters: s-t-r-a-w-b-e-r-r-y (10 letters total). 2. I checked each letter for 'r'. 3. The first 'r' is in position 3, in "str…". 4. The second and third 'r's are in positions 8 and 9, in the "…rry" ending. **Answer: There are 3 r's in "strawberry".** A common mistake is to see "berry" as having only one 'r' (or to treat the double-r as a single letter), which leads to the incorrect answer of 2.

3.1s response332 output tokens

Debug This Error

I'm getting the following error in my Node.js application: TypeError: Cannot read properties of undefined (reading 'map') at UserList (/app/components/UserList.js:12:25) at renderWithHooks (/app/node_modules/rea…

## Cause `users` is `undefined` when the component renders, so `users.map(...)` throws. This happens when: 1. **The parent doesn't pass the prop**, or passes it under a different name (e.g. `<UserList data={x} />` or a typo like `user=`). 2. **The data loads asynchronously.** On the first render, the state or fetch result hasn't arrived yet. 3. **The value is wrong.** For example, the API returns `{ users: [...] }` and you passed the whole object, or you're reading a property that doesn't exist (`response.data.users` vs `response.users`). ## Fixes ### 1. Default value (simplest) ```jsx function UserList({ users = [] }) { return ( <ul> {users.map(user => <li key={user.id}>{use…

6.7s response824 output tokens

Code Review

Please review the following Python function and suggest improvements for readability, performance, and best practices: def get_data(url, retries=3): import requests import time for i in range(retries):…

# Code Review ## Main Issues ### 1. Bare `except:` hides bugs (most important) It catches everything, including `KeyboardInterrupt` and `SystemExit`. It also wraps your parsing logic, so a missing `"active"` key (`KeyError`) or bad JSON is treated as a network failure, retried 3 times with sleeps, and then silently becomes `[]`. Catch only `requests.RequestException`, and keep parsing outside the `try`. ### 2. Silent failure Returning `[]` after all retries fails is indistinguishable from "the server returned no active items." Callers can't tell whether something went wrong. Raise an exception (or at least log) once retries are exhausted. ### 3. Retry logic - It sleeps after the final at…

20.9s response3003 output tokens

Compare these answers side by side with other models →

Frequently asked questions

How much does the Claude Sonnet 5.5 API cost?: On FastMetal, Claude Sonnet 5.5 is billed per token in yen: ¥357.4 per 1M input tokens and ¥1,787 per 1M output tokens, before tax. Usage is drawn from a prepaid balance; there is no subscription or monthly fee.
Can I call Claude Sonnet 5.5 with the OpenAI SDK?: Yes. Point base_url at https://api.fastmetal.ai/v1 and pass "anthropic-claude-sonnet-5-5" as the model; existing OpenAI-style code works unchanged, including streaming, tool calls and structured output.
What is the context window of Claude Sonnet 5.5?: 1,000,000 tokens, shared between the prompt and the response.
What do I need to try Claude Sonnet 5.5?: Create an account and add credit; the model is then available both in the browser chat and over the API. There is no contract or minimum spend.