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Claude Sonnet 4.5

AnthropicReleased Sep 29, 2025

Claude Sonnet 4.5 is Anthropic’s most advanced Sonnet model to date, optimized for real-world agents and coding workflows. It delivers state-of-the-art performance on coding benchmarks such as SWE-bench Verified, with...

Try in playground
Context window
1M tokens
Max output
64K tokens
Input
text, image, file
Output
text
Tokenizer
Claude
Knowledge cutoff
Jan 31, 2025
Released
Sep 29, 2025
Reasoning
optional

Pricing

Per 1M tokens. The provider price and our flat 3% fee are separate columns — what you pay is their sum.

Per 1M tokensProvider+ 3% feeYou pay
Input$3.00$0.090$3.09
Output$15.00$0.450$15.45
Cache read$0.300$0.0090$0.309
Cache write$3.75$0.112$3.86

Benchmarks

Design Arena

CategoryEloWin rateRank
3Dmodels123653.5%#34
ASCII artmodels124956.8%#10
Codemodels123253%#34
Data vizmodels121149.3%#42
Game devmodels123352.1%#37
SVGmodels117353%#37
UI componentsmodels123452.3%#35
Websitesmodels123253.4%#38
Full-stackagents112043.5%#18
Mobile appsagents118448.9%#21
Web appsagents112943.1%#21

Head-to-head preference voting. How we filter and rank

Supported parameters

  • include_reasoning
  • max_tokens
  • reasoning
  • response_format
  • stop
  • structured_outputs
  • temperature
  • tool_choice
  • tools
  • top_k
  • top_p

Call it

OpenAI-compatible: point your SDK at api.openkey.ai/v1 and use model anthropic/claude-sonnet-4.5.

Code sample language
curl https://api.openkey.ai/v1/chat/completions \
  -H "Authorization: Bearer $OPENKEY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "anthropic/claude-sonnet-4.5",
    "messages": [{"role": "user", "content": "Hello"}]
  }'
import os
from openai import OpenAI

client = OpenAI(
    base_url="https://api.openkey.ai/v1",
    api_key=os.environ["OPENKEY_API_KEY"],
)

completion = client.chat.completions.create(
    model="anthropic/claude-sonnet-4.5",
    messages=[{"role": "user", "content": "Hello"}],
)
print(completion.choices[0].message.content)
import OpenAI from "openai";

const client = new OpenAI({
  baseURL: "https://api.openkey.ai/v1",
  apiKey: process.env.OPENKEY_API_KEY,
});

const completion = await client.chat.completions.create({
  model: "anthropic/claude-sonnet-4.5",
  messages: [{ role: "user", content: "Hello" }],
});
console.log(completion.choices[0].message.content);

Questions

How much does Claude Sonnet 4.5 cost via API?
Through OpenKey, Claude Sonnet 4.5 costs $3.09 per 1M input tokens and $15.45 per 1M output tokens. That is the provider price ($3.00 / $15.00) plus a flat 3% fee — nothing else.
What is Claude Sonnet 4.5's context window?
Claude Sonnet 4.5 accepts up to 1M tokens of context and returns up to 64K tokens per request.
Is Claude Sonnet 4.5 OpenAI-compatible?
Yes. Send requests to OpenKey's /v1/chat/completions endpoint with model "anthropic/claude-sonnet-4.5" using any OpenAI SDK — only the base URL and API key change.
What inputs does Claude Sonnet 4.5 support?
Claude Sonnet 4.5 accepts text, image, file input and produces text output. Its knowledge cutoff is Jan 31, 2025.

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