Claude Sonnet 4.5

Anthropic’s Claude Sonnet 4.5 via OpenAI-compatible API. The best coding model with excellent speed-to-performance ratio.

Claude Sonnet 4.5 is Anthropic’s best coding model, available through AnyFast via an OpenAI-compatible interface. It delivers an excellent balance of speed and capability, excelling at code generation, analysis, writing, and complex reasoning tasks.

Key capabilities

• OpenAI-compatible — Works as a drop-in replacement with the OpenAI SDK
• Best coding model — Top performance on code generation, refactoring, and debugging
• Fast and capable — Excellent speed-to-performance ratio
• Long context — Handles large documents and multi-turn conversations
• Streaming — Supports real-time token streaming via SSE
• Strong reasoning — Designed for complex, multi-step tasks

Quick example

cURL

curl https://www.anyfast.ai/v1/messages \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-5-20250929",
    "messages": [
      { "role": "user", "content": "Explain quantum entanglement in simple terms." }
    ]
  }'

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://www.anyfast.ai/v1"
)

response = client.chat.completions.create(
    model="claude-sonnet-4-5-20250929",
    messages=[
        {"role": "user", "content": "Explain quantum entanglement in simple terms."}
    ]
)

print(response.choices[0].message.content)

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://www.anyfast.ai/v1"
)

stream = client.chat.completions.create(
    model="claude-sonnet-4-5-20250929",
    messages=[
        {"role": "user", "content": "Write a short poem about the sea."}
    ],
    stream=True
)

for chunk in stream:
    print(chunk.choices[0].delta.content or "", end="")

Parameters

Parameter	Type	Required	Description
model	string	Yes	Must be claude-sonnet-4-5-20250929
messages	array	Yes	List of { role, content } objects
max_tokens	integer	No	Maximum tokens to generate
temperature	float	No	0–2. Controls randomness. Default: 1
stream	boolean	No	Enable SSE streaming. Default: false
top_p	float	No	Nucleus sampling threshold. Default: 1
stop	string / array	No	Sequences that stop generation

API Reference

View the interactive API playground for Claude Sonnet 4.5.