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

temperature, top_p, and top_k are not supported on Claude Opus 4.8. Setting them to non-default values returns a 400 error. Use prompting to guide the model’s behavior.

API Reference

View the interactive API playground for Claude Opus 4.8.

​Key capabilities

​Quick example

​Parameters

API Reference

Key capabilities

Quick example

Parameters