Claude Sonnet 4.5
Access Claude Sonnet 4.5 through one API key. Previous-gen Anthropic flagship.
Previous-gen Claude Sonnet model. Still a capable all-rounder with strong reasoning and 1M context.
No credit card required. Takes 30 seconds.
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 4.5 respond in real time.
Maximum tokens in the response.
Real-time tokens
Context Window
1M tokens
Max Output
64K tokens
Input Price
$4.20 / 1M tokens
Output Price
$21.00 / 1M tokens
Strengths
Anthropic's tuning delivers reliable multi-step reasoning and instruction following across complex tasks, with a 1M-token context window.
Strong code generation, review, and multi-file editing, a long-standing strength of the Claude Sonnet line.
Produces clear, well-structured long-form writing and editing with consistent tone and nuance.
Handles document analysis and synthesis over very large inputs, supported by the 1M context and 64K output ceiling.
Quick start
Copy this snippet and start making calls with Claude Sonnet 4.5.
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-4.5",
"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 4.5 through YepAPI?
Claude Sonnet 4.5 API: Anthropic's capable all-rounder
Claude Sonnet 4.5 is a previous-generation Anthropic Sonnet model and still a strong all-rounder, with reliable reasoning, coding, and writing plus a 1M-token context window. YepAPI serves it through one OpenAI-compatible endpoint.
Your single YepAPI key also reaches DeepSeek, Grok, Gemini, Kimi, and more, plus SEO, SERP, and scraping endpoints, so you can blend Claude's quality with cheaper models in the same workflow.
What is Claude Sonnet 4.5?
Claude Sonnet 4.5 is a previous-generation model in Anthropic's Claude Sonnet family, and remains a capable, well-rounded option for reasoning, coding, writing, and analysis. It carries a 1,000,000-token context window with up to 64,000 output tokens, so it can work over large codebases and document sets while keeping Anthropic's reputation for careful instruction following and coherent long-form output. As an earlier flagship, it offers strong quality at lower pricing than current-generation Anthropic models, which makes it a practical pick when you want Claude-style reliability without paying for the newest release.
Build with Claude Sonnet 4.5 via YepAPI
Use YepAPI's OpenAI-compatible /v1/ai/chat endpoint with any OpenAI client; no Anthropic-specific SDK is needed. Set the base URL, add your key, and set the model string to Claude Sonnet 4.5. Switching from any other model is a single string change. Because one key reaches the full catalog, you can route quality-sensitive reasoning and writing to Claude Sonnet 4.5 and send bulk or budget work to cheaper models from the same integration.
Claude Sonnet 4.5 API pricing — $4.20 input / $21.00 output per 1M tokens
Claude Sonnet 4.5 costs $4.20 per 1M input tokens and $21.00 per 1M output tokens. As an Anthropic model it sits at the premium end of the catalog, reflecting its quality on reasoning, coding, and writing, but as a previous-generation Sonnet it is cheaper than current Anthropic flagships. Per-token billing lets you reserve it for the high-value tasks where its quality pays off.
Claude Sonnet 4.5 for coding and long-document analysis
Claude Sonnet 4.5 is well suited to multi-file code generation and review, careful long-form writing and editing, and analysis over large inputs. The 1M context window lets it reason across whole repositories or document collections, and Anthropic's instruction-following strength makes it dependable for tasks where accuracy and tone matter more than raw cost, such as customer-facing content and code that needs to be right.
Try Claude Sonnet 4.5 free
New YepAPI accounts come with $5 in free credit and no card required. That lets you test Claude Sonnet 4.5 on your real reasoning, coding, and writing prompts, compare its quality against cheaper models on the same key, and decide where it earns its place before adding payment.
Start generating in 30 seconds
$5 free credit on signup. No credit card required. Pay per call.
What developers say
“Switched from SerpAPI and cut our SERP costs by 80%. Same data quality, way simpler billing.”
“One API key for AI models, SERP data, and web scraping. Saved us from managing 4 separate providers.”
“The $5 free credit let us prototype our entire rank tracking feature before committing. No other API does that.”
Frequently asked questions
Previous-gen Claude Sonnet model. Still a capable all-rounder with strong reasoning and 1M context.
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.
Sign up for a free API key, then send requests to the /v1/ai/chat endpoint.
Claude Sonnet 4.5 supports a 1M token context window with up to 64K output tokens per request.
Ready to use Claude Sonnet 4.5?
$5 free credit on signup. No credit card required. Pay per call.
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