AnthropicText Generation/v1/ai/chat

Claude Sonnet 5.5 API

Access Claude Sonnet 5.5 through one API key. Anthropic Everyday Sonnet-Class Model.

Claude Sonnet 5.5 is Anthropic's Sonnet-class model for well-scoped everyday work, a direct upgrade to Claude Sonnet 5 at the same price. It is the practical default Claude for building features, fixing bugs, reviewing code and writing long documents, with Opus kept for the hardest problems.

Full Docs Get API Key — Free $5 Credit

No credit card required. Takes 30 seconds.

Claude Sonnet 5.5 API pricing

Pay per request from your YepAPI balance — no subscription, no monthly minimum. Prices updated October 23, 2026.

Token type	Price
Input	$2.95 / 1M tokens
Output	$14.77 / 1M tokens
Context window	1M tokens

What it costs	Per job	Per 1,000
Chat reply1K input + 500 output tokens	$0.01	$10.33
RAG answer8K input + 800 output tokens	$0.035	$35.42
Agent step with tools30K input + 2K output tokens	$0.118	$118.04
Long document summary100K input + 2K output tokens	$0.325	$324.54

2,400+

Developers

1.2M+

API calls served

100+

Endpoints

$0.01

Per call

Yep, that's it.

Try it live

Send a message and see Claude Sonnet 5.5 respond in real time.

POST/v1/ai/chatanthropic/claude-sonnet-5.5

Message *

Max Tokens

Maximum tokens in the response.

Stream

Real-time tokens

Hit "Send Request" to see the response

Claude Sonnet 5.5 specs

Provider	Anthropic
Model ID	anthropic/claude-sonnet-5.5
Endpoint	/v1/ai/chat
Type	Text Generation
Context window	1M tokens
Max output	128K tokens
Reasoning	No
OpenAI-compatible	Yes — /v1/ai/chat/completions

How to get a Claude Sonnet 5.5 API key

1
Create a free account
Sign up at yepapi.com with Google or email. It takes about 30 seconds and needs no card.
2
Create an API key
Open the dashboard, go to API Keys and create a key. Copy it — it starts with yep_sk_.
3
Call Claude Sonnet 5.5
Send a request to /v1/ai/chat with the x-api-key header and model "anthropic/claude-sonnet-5.5".
4
Pay as you go
Usage is billed per request from your balance. Top up any amount; there is no subscription.

Strengths

✓

Direct upgrade to Sonnet 5

Stronger coding and writing than Claude Sonnet 5 at the same $2.95 / $14.77 per 1M tokens, so switching is a one-string change.

✓

1M token context

Reads up to 1,000,000 tokens in one request, enough for a large codebase or a long contract with its exhibits.

✓

Features and bug fixes

Particularly good at building features and fixing bugs from a clear description, with edits that fit the surrounding code.

✓

Tools and structured output

Function calling, JSON schema outputs and adjustable reasoning for agent loops and pipelines.

Quick start

Copy this snippet and start making calls with Claude Sonnet 5.5.

const res = await fetch('https://api.yepapi.com/v1/ai/chat', {
  method: 'POST',
  headers: {
    'x-api-key': 'YOUR_API_KEY',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    "model": "anthropic/claude-sonnet-5.5",
    "messages": [
      {
        "role": "user",
        "content": "Explain API gateways in 2 sentences."
      }
    ],
    "maxTokens": 256
  }),
});
const { data } = await res.json();
console.log(data.message.content);

Claude Sonnet 5.5 vs similar models

Every model below runs on the same API key — switch by changing the model ID.

Model	Provider	Price	Context
Claude Sonnet 5.5	Anthropic	$2.95 in / $14.77 out per 1M	1M
Claude Haiku 5.5	Anthropic	$0.15 in / $0.74 out per 1M	1M
Claude Haiku 4.5	Anthropic	$1.48 in / $7.38 out per 1M	200K
Claude Sonnet 5	Anthropic	$2.95 in / $14.77 out per 1M	1M
Claude Sonnet 4.6	Anthropic	$4.43 in / $22.15 out per 1M	1M
Claude Sonnet 4.5	Anthropic	$4.43 in / $22.15 out per 1M	1M
Nemotron 3 Super	NVIDIA	$0 in / $0 out per 1M	262K
Qwen3.7 Flash	Qwen	$0.04 in / $0.19 out per 1M	1M

Why use Claude Sonnet 5.5 through YepAPI?

✓One API key for all models — no separate accounts

✓OpenAI SDK compatible — just change the base URL

✓No monthly minimums — pay per token

✓Switch models with one line of code

✓Full provider passthrough — citations, search results, and all extras included

✓Streaming and non-streaming support on every model

✓Works with Cursor, Claude, LangChain, and any LLM tool

✓Unified billing across all providers

Claude Sonnet 5.5 API — pricing, context window & access

Claude Sonnet 5.5 is Anthropic's Sonnet-class model for well-scoped everyday work, a direct upgrade to Claude Sonnet 5 at the same price. It pairs a 1,000,000-token context window with up to 128,000 output tokens per response, at $2.95 per 1M input and $14.77 per 1M output tokens through YepAPI.

Through YepAPI you call Claude Sonnet 5.5 on an OpenAI-compatible endpoint with a single key — the same key that reaches GPT-6, Claude, Gemini, Grok and the SEO, SERP and scraping APIs. Input: text, images, files.

What is Claude Sonnet 5.5?

Claude Sonnet 5.5 is Anthropic's Sonnet-class model for well-scoped everyday work, a direct upgrade to Claude Sonnet 5 at the same price. It is strongest on clearly scoped engineering tasks: implementing a feature from a spec, tracking down a bug, or producing polished long-form writing in one pass. It accepts text, images, files as input, handles up to 1,000,000 tokens of context and returns up to 128,000 output tokens per call.

Build with Claude Sonnet 5.5 via YepAPI

YepAPI serves Claude Sonnet 5.5 on the OpenAI-compatible /v1/ai/chat endpoint. Point your base URL at YepAPI, add your key, and set the model string to claude-sonnet-5.5 (or the full anthropic/claude-sonnet-5.5). Function calling, structured outputs and reasoning settings pass straight through, and switching to any other model on the platform is a one-string change per request.

Claude Sonnet 5.5 API pricing — $2.95 / 1M input, $14.77 / 1M output

Claude Sonnet 5.5 costs $2.95 per 1M input tokens and $14.77 per 1M output tokens through YepAPI, pay per token with no minimums. Failed calls are never charged, and every request is itemised in your dashboard API Logs.

Claude Sonnet 5.5 use cases

It is the practical default Claude for building features, fixing bugs, reviewing code and writing long documents, with Opus kept for the hardest problems.

Try Claude Sonnet 5.5 free

Every new YepAPI account includes $5 in free credit with no card required — enough to test Claude Sonnet 5.5 on your own prompts before committing to paid usage. Create an account, copy your key, and call claude-sonnet-5.5 right away.

Start generating in 30 seconds

$5 free credit on signup. No credit card required. Pay per call.

Get API Key

What developers say

“Switched from SerpAPI and cut our SERP costs by 80%. Same data quality, way simpler billing.”
Marcus T.
SEO Platform Founder

“One API key for AI models, SERP data, and web scraping. Saved us from managing 4 separate providers.”
Priya S.
Full-Stack Developer

“The $5 free credit let us prototype our entire rank tracking feature before committing. No other API does that.”
Jake R.
Indie Hacker

Frequently asked questions

Claude Sonnet 5.5 costs $2.95 per 1M input tokens and $14.77 per 1M output tokens through YepAPI, billed per request with no monthly fee. For example, a chat reply (1K input + 500 output tokens) costs about $0.01.

Sign up at yepapi.com (Google or email, about 30 seconds), open the dashboard and create an API key. The same key works for Claude Sonnet 5.5 and every other model — no separate Anthropic account or waitlist.

New YepAPI accounts in most countries get free signup credit, enough to test Claude Sonnet 5.5 without a card. After that you pay per request at the rates above — there is no subscription.

Use "anthropic/claude-sonnet-5.5" as the model on /v1/ai/chat. The short alias "claude-sonnet-5.5" also works.

Yes. Point the OpenAI SDK at https://api.yepapi.com/v1/ai with your YepAPI key and set model to "anthropic/claude-sonnet-5.5". Streaming works the same way, so existing OpenAI code only needs the base URL and key changed.

Claude Sonnet 5.5 supports a 1M token context window with up to 128K output tokens per request.