Claude Opus 4.8

Claude Opus 4.8 is Anthropic’s most capable generally available model, available through AnyFast via an OpenAI-compatible interface. It builds on Claude Opus 4.7 with improved long-horizon agentic coding, more reliable tool triggering, and better compaction handling.

Key capabilities

OpenAI-compatible — Works as a drop-in replacement with the OpenAI SDK
1M context window — 128K max output tokens
Adaptive thinking — Smart reasoning that triggers only when the task needs it
Fast mode — Up to 2.5x higher output speed at premium pricing (research preview)
Mid-conversation system messages — Append updated instructions without restating the full system prompt
Lower cache minimum — 1,024 token minimum cacheable prompt length
Streaming — Supports real-time token streaming via SSE

Quick example

curl https://www.anyfast.ai/v1/messages \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-opus-4-8",
    "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-opus-4-8",
    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-opus-4-8",
    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-opus-4-8`
`messages`	array	Yes	List of `{ role, content }` objects
`max_tokens`	integer	No	Maximum tokens to generate
`stream`	boolean	No	Enable SSE streaming. Default: `false`
`stop`	string / array	No	Sequences that stop generation

Claude Opus 4.8 does not support custom sampling values. Omit temperature, top_p, and top_k for normal requests. For backward compatibility, temperature: 1 and top_p values from 0.99 to 1 are accepted; any top_k value or other sampling value returns a 400 error. Use prompting to guide model behavior. See Anthropic’s API parameter deprecations.

API Reference

View the interactive API playground for Claude Opus 4.8.

Getting started

Model Introduction

Resources

Claude Opus 4.8

Key capabilities

Quick example

Parameters

API Reference

​Key capabilities

​Quick example

​Parameters

API Reference

Key capabilities

Quick example

Parameters