How do I use Claude Sonnet 4 through YepAPI?

Sign up for a free API key, then send requests to the /v1/ai/chat endpoint.

AnthropicText Generation/v1/ai/chat

Claude Sonnet 4

Access Claude Sonnet 4 through one API key. Anthropic's best balance of speed and intelligence.

Anthropic's balanced model. Excellent at writing, analysis, coding, and complex multi-step tasks with a massive context window.

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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 4 respond in real time.

POST/v1/ai/chatanthropic/claude-sonnet-4

Message *

Max Tokens

Maximum tokens in the response.

Stream

Real-time tokens

Hit "Send Request" to see the response

Context Window

200K tokens

Max Output

8K tokens

Input Price

$4.20 / 1M tokens

Output Price

$21.00 / 1M tokens

Strengths

✓

Excellent writing

Produces clear, well-structured long-form prose and editing with a natural voice, drawing on a 200K-token context for source material.

✓

Complex analysis

Strong at synthesizing long documents, comparing trade-offs, and reasoning through multi-step problems within its 200K-token window.

✓

Code generation

Anthropic tunes Sonnet heavily for coding — generating, refactoring, and explaining code across languages with reliable instruction-following.

✓

200K context window

Holds roughly 150,000 words in a single request, enough for large codebases, contracts, or report sets without chunking.

Quick start

Copy this snippet and start making calls with Claude Sonnet 4.

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-4",
    "messages": [
      {
        "role": "user",
        "content": "Explain API gateways in 2 sentences."
      }
    ],
    "maxTokens": 256
  }),
});
const { data } = await res.json();
console.log(data.message.content);

Why use Claude Sonnet 4 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 4 API — pricing, context window & access

Claude Sonnet 4 is Anthropic's balanced model, tuned to land between speed and frontier intelligence. It carries a 200K-token context window and returns up to 8,192 output tokens per response.

Through YepAPI you call Claude Sonnet 4 on an OpenAI-compatible endpoint with one key — the same key that also reaches GPT-4o, Gemini, the rest of the Claude family, and the SEO, SERP and scraping endpoints.

What is Claude Sonnet 4?

Claude Sonnet 4 is Anthropic's mid-tier model, positioned between the fast, cheap Haiku and the top-end Opus. It's built to be the everyday workhorse of the Claude family: excellent at writing and editing, strong at multi-step analysis, and one of the better coding models at its price. Its defining trait is a 200K-token context window — large enough to load entire codebases, long contracts, or stacks of documents in a single call. Teams pick Sonnet when they want most of Claude's intelligence without paying flagship rates.

Build with Claude Sonnet 4 via YepAPI

YepAPI exposes Claude Sonnet 4 through the OpenAI-compatible /v1/ai/chat endpoint, so you call Anthropic's model using the chat-completions format and the model string claude-sonnet-4 — no Anthropic SDK required. Switching to Claude Haiku, Claude Opus, GPT-4o, or Gemini later is a single string change. Your one key also covers search and scraping endpoints, letting writing tools, code assistants, and data pipelines all run on the same account.

Claude Sonnet 4 API pricing — $4.20 / 1M input, $21.00 / 1M output

Claude Sonnet 4 costs $4.20 per 1M input tokens and $21.00 per 1M output tokens through YepAPI. Because its 200K window lets you send very large prompts, watch input volume on big-document jobs — but the input rate stays modest relative to flagship models. You pay only for tokens consumed, so it's economical to feed Sonnet long source material and let it write or analyze against the full context in one pass.

Claude Sonnet 4 for writing & long-context analysis

Sonnet 4 is a natural fit when the job mixes long inputs with high-quality output. Load a 200K-token window with a codebase, contract set, or research corpus and ask it to refactor, summarize, or compare — it reasons across the whole context without chunking. Its writing quality also makes it strong for drafting, rewriting, and editing where tone and structure matter, which is why many teams default to Sonnet for content and coding alike.

Try Claude Sonnet 4 free

New YepAPI accounts come with $5 in free credit and no card required. That's enough to test Sonnet 4 on a real long-context document or coding task before committing. Sign up, grab your key, and call Claude Sonnet 4 within minutes.

Start generating in 30 seconds

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

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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

Anthropic's balanced model. Excellent at writing, analysis, coding, and complex multi-step tasks with a massive context window.

Input tokens cost $4.20 per 1M tokens and output tokens cost $21.00 per 1M tokens through YepAPI. No monthly minimums — you only pay for what you use.

Claude Sonnet 4 supports a 200K token context window with up to 8K output tokens per request.