Claude Sonnet 4.5
Claude Sonnet 4.5 is Anthropic's model excelling at coding and agent building, with strong finance, law, medicine, and STEM knowledge. Access it through Velokey's unified endpoint with below-list pricing.
Use cases
Complex software engineering & modernization · Finance / legal / medical analysis
Input
Text
Output
Text
Billing
Per token
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Sign up to get $0.5 in free credits — about 20 free images
Pricing details
Transparent usage-based pricing with no hidden fees.
Detailed Pricing
Usage-based pricing breakdown
| Spec | Price | Official | Savings |
|---|---|---|---|
| Input/1M tokens | 2.4 Credits≈$2.4 | 3 Credits | -20% |
| Output/1M tokens | 12 Credits≈$12 | 15 Credits | -20% |
| Cache Read/1M tokens | 0.24 Credits≈$0.24 | 0.3 Credits | -20% |
| Cache Write/1M tokens | 3 Credits≈$3 | 3.75 Credits | -20% |
Billing Rules
- Output price varies by model, resolution, quality, duration, or token usage.
- Uploaded reference files may be charged separately when supported.
- Add-on capabilities such as web search or image search may be billed per request.
- Token-based models are billed by input and output tokens.
- If the primary route is unavailable, Velokey may automatically switch to a stable fallback route when possible.
- Usage is pay-as-you-go with transparent credit deduction.
* Final cost depends on the generated result.
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Affordable Claude Sonnet 4.5 API
Access Anthropic's Sonnet 4.5 on Velokey — top-tier coding, 30+ hours of focus, the strongest agent building, and multi-domain expertise, with a unified endpoint and below-list pricing for production apps.
Meet Claude Sonnet 4.5 and its API access
Claude Sonnet 4.5 is Anthropic's model released on September 29, 2025, excelling at coding, agent building, computer use, and domain expertise. It reaches 77.2% on SWE-bench Verified, sustains 30+ hours of focus on complex multi-step tasks, drops code-edit error rate to 0%, and supports parallel tool calls — with stronger domain knowledge across finance, law, medicine, and STEM, and the most robust alignment of any frontier model at release. Velokey provides an affordable, easy-to-integrate Claude Sonnet 4.5 API: a unified chat endpoint, a clear request flow, and below-list pricing for production systems, agent pipelines, and automation tools.
Top-tier coding & 30+ hours of focus
Reaches 77.2% on SWE-bench Verified and sustains 30+ hours of continuous focus on complex multi-step tasks, with code-edit error rate down to 0% (from 9% on Sonnet 4) — fit for long autonomous engineering runs.
View Documentation →
Strong computer use
Reaches 61.4% on OSWorld computer use (up from Sonnet 4's 42.2%), performing browser navigation, form filling, and task completion — fit for automating web and desktop work.
View Documentation →
Strongest agent building & parallel tools
Described as the strongest model for building complex agents, with the Claude Agent SDK, parallel tool calls, and longer-context task handling that keep multi-step autonomous flows stable.
View Documentation →
Multi-domain expertise & robust alignment
Stronger domain knowledge across finance, law, medicine, and STEM for investment-grade analysis, while being the most aligned frontier model at release — reduced sycophancy and deception, with better prompt-injection defenses.
View Documentation →
How to deploy the Claude Sonnet 4.5 API on Velokey
Get started with just a few steps.
Sign up and get an API Key
Sign in to the Velokey console to generate an API Key that authenticates every request sent to Claude Sonnet 4.5.
Configure request parameters
Set model to claude-sonnet-4-5 and submit messages. Enable extended thinking for deeper reasoning; for agents, pair it with the Claude Agent SDK and parallel tool calls.
Integrate and start calling
Send requests to Velokey's unified /v1/chat/completions endpoint to power assistants, agents, and automation, with usage managed in one console.
Real-world use cases for Claude Sonnet 4.5
From engineering to domain analysis, covering many high-autonomy scenarios.
Complex software engineering & modernization
Top-tier coding — fit for development, refactoring, and modernization across large codebases and long autonomous runs.
Complex agents & automation
The strongest model for building complex agents, with the Agent SDK and parallel tools — fit for multi-step autonomous flows.
Computer use & browser automation
Leads on OSWorld — fit for web navigation, form filling, and desktop task automation.
Finance & investment-grade analysis
Stronger finance domain knowledge — fit for investment-grade financial analysis and other high-reliability work.
Legal & medical analysis
Stronger legal and medical domain knowledge — fit for professional analysis that demands rigor.
STEM & cybersecurity
Improved STEM reasoning and math — fit for scientific computation and cybersecurity red teaming.
Why choose Velokey for Claude Sonnet 4.5
Discount on list price
Call Claude Sonnet 4.5 at a lower price on Velokey — pay-as-you-go with no forced subscription, reducing upfront cost.
Unified API interface
One API Key accesses Claude Sonnet 4.5 and other models — no juggling multiple accounts and keys, simplifying integration.
Complete docs and migration guidance
Endpoint references, parameter details, and migration examples help you quickly adopt extended thinking and agent building.
Stable and highly available
Automatic failover and stable fallback routes maintain availability when the primary route is down, keeping production reliable.
API Reference
Complete API call examples and parameter descriptions
Endpoint
https://api.velokey.ai/v1/messagesAuthentication
Bearer YOUR_API_KEYRequest Example
curl https://api.velokey.ai/v1/messages \
-X POST \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "claude-sonnet-4-5-20250929",
"messages": [{"role": "user", "content": "Hello!"}],
"temperature": 0.7
}'Response Example
{
"id": "req_abc123",
"model": "claude-sonnet-4-5-20250929",
"created": 1234567890,
"data": { ... }
}Claude Sonnet 4.5 API FAQ
What stands out about Claude Sonnet 4.5?
It was among the best coding models at release (77.2% on SWE-bench Verified), sustains 30+ hours of focus on complex tasks, drops code-edit error rate to 0%, and excels at agent building, computer use, and finance/law/medicine/STEM domain knowledge — while being the most aligned frontier model at release.
Is it good at building agents?
Yes. Sonnet 4.5 is described as the strongest model for building complex agents, with the Claude Agent SDK, parallel tool calls, longer-context task handling, and better multi-step reasoning.
What can computer use do?
It reaches 61.4% on OSWorld, performing computer-use actions like browser navigation, form filling, and task completion — fit for automating web and desktop flows.
Which domains is it good for?
It has stronger domain knowledge across finance, law, medicine, and STEM, suitable for investment-grade financial analysis and other high-reliability professional work.
How is it billed on Velokey?
Official pricing is $3 input / $15 output per million tokens, the same as Sonnet 4. This page's pricing area shows the current Velokey price, billed by input and output tokens with a discount on list price.
Start building with Claude Sonnet 4.5 today
Use one API key to access low-cost, stable AI models through Velokey.