Anthropic Language Popular

Claude Sonnet 4.5

Balanced Claude 4.5 model for complex reasoning

1M Context window

Text + Vision Modalities

General Specialty

Yes Streaming

Get API key — free View docs →

Model ID claude-sonnet-4-5-20250929 /v1/chat/completions

Our pricing

Input tokens per 1M tok

$2.40

Output tokens per 1M tok

$12.00

Pay-as-you-go · No minimums · Cancel anytime

OpenAI-compatible ( api.belugapi.com/v1)

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No credit card required to test

Capabilities

What Claude Sonnet 4.5
can do for you.

Native API parity with the official provider — every feature surfaced one-to-one.

Streaming

Server-sent events out of the box

Vision

Analyze images, charts & documents

Reasoning

Deep chain-of-thought for hard tasks

Long context

200K+ tokens of working memory

Integration

2-line migration.
Zero friction.

BelugAPI is 100 % compatible with the OpenAI SDK. Point base_url to our endpoint and you're done — no refactoring, no learning curve.

Same request & response schema

Python · Node.js · REST · Go · Ruby

Streaming, tool-calling, structured output

Automatic failover & load balancing

Python

from openai import OpenAI

client = OpenAI(
  api_key=bel-your-key,
  base_url=https://api.belugapi.com/v1
)

response = client.chat.completions.create(
  model=claude-sonnet-4-5-20250929,
  messages=[{"role": user, "content": Hello!}]
)
print(response.choices[0].message.content)

Node.js

import OpenAI from openai;

const client = new OpenAI({
  apiKey:  bel-your-key,
  baseURL: https://api.belugapi.com/v1,
});

const res = await client.chat.completions.create({
  model:    claude-sonnet-4-5-20250929,
  messages: [{ role: user, content: Hello! }],
});
console.log(res.choices[0].message.content);

cURL

curl https://api.belugapi.com/v1/v1/chat/completions \
  -H Authorization: Bearer bel-your-key \
  -H Content-Type: application/json \
  -d {"model":"claude-sonnet-4-5-20250929","messages":[{"role":"user","content":"Hello!"}]}

Highlights

Built for production.

Complex reasoning

Complete guide

Everything about
Claude Sonnet 4.5.

Specifications, pricing, capabilities, and integration tips — kept up to date with every Anthropic release.

By Anthropic 2 min read Updated May 2026

Balanced Claude 4.5 model for complex reasoning

Overview

Claude Sonnet 4.5 is a cutting-edge large language model (llm) developed by Anthropic, designed to push the boundaries of artificial intelligence-powered content generation.

This model excels in complex reasoning, making it a top choice for professionals seeking high-quality, scalable AI solutions. Whether you're building production applications, researching new AI capabilities, or creating stunning visual content, Claude Sonnet 4.5 delivers industry-leading performance and reliability.

Key Specifications

Specification	Details
Model Name	Claude Sonnet 4.5
Provider	Anthropic
Category	Large Language Model (LLM)
Model Type	Chat
Context Window	200K

Pricing

Input: $2.4/M tokens
Output: $12/M tokens

Key Features & Capabilities

Complex Reasoning: Advanced capability for professional-grade output.

Use Cases & Applications

Customer support chatbots
Content creation and writing assistants
Knowledge base Q&A systems
Educational tutoring platforms

Frequently asked questions

What is Claude Sonnet 4.5 best used for?

Claude Sonnet 4.5 excels at complex reasoning, making it ideal for professional and enterprise applications.

Who developed Claude Sonnet 4.5?

Claude Sonnet 4.5 was developed by Anthropic, a leading AI research and development company.

How do I integrate Claude Sonnet 4.5 into my application?

You can integrate Claude Sonnet 4.5 via its official API endpoint using standard HTTP requests with your API key. SDKs are available for Python, JavaScript, and other languages.

What is the pricing model for Claude Sonnet 4.5?

Pricing is based on input. Check the pricing section above for detailed rates.

Ready to ship? Start using Claude Sonnet 4.5 in under 30 seconds.

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