Claude Opus 5

Claude Opus 5 is Anthropic’s Opus model for complex agentic coding and enterprise work, available through AnyFast via the native Anthropic Messages API. Compared with Claude Opus 4.8, it improves deep reasoning, long-horizon tool use, code review, vision, and multi-agent coordination.

Key capabilities

1M context window — 1M tokens by default, with 128K max output tokens
Adaptive thinking — On by default; control depth with output_config.effort
Five effort levels — Choose low, medium, high, xhigh, or max; the default is high
Agentic coding — Handles multi-file features, large refactors, code review, and long-running tool workflows
Vision and long context — Understands images, charts, documents, and diagrams across long inputs
Tools and streaming — Supports tool use and real-time SSE responses through the Messages API
Model ID — Use claude-opus-5

Quick example

curl https://www.anyfast.ai/v1/messages \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-opus-5",
    "max_tokens": 4096,
    "output_config": { "effort": "high" },
    "messages": [
      { "role": "user", "content": "Write a Python function to merge two sorted arrays." }
    ]
  }'

import anthropic

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

message = client.messages.create(
    model="claude-opus-5",
    max_tokens=4096,
    output_config={"effort": "high"},
    messages=[
        {"role": "user", "content": "Write a Python function to merge two sorted arrays."}
    ]
)

print(message.content[0].text)

import anthropic

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

with client.messages.stream(
    model="claude-opus-5",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Explain the difference between async and sync programming."}
    ],
) as stream:
    for text in stream.text_stream:
        print(text, end="")

Parameters

Parameter	Type	Required	Description
`model`	string	Yes	Must be `claude-opus-5`
`messages`	array	Yes	List of `{ role, content }` objects
`max_tokens`	integer	Yes	Maximum tokens to generate. Claude Opus 5 supports up to 128K output tokens.
`output_config`	object	No	Use `{"effort":"low" \| "medium" \| "high" \| "xhigh" \| "max"}` to control adaptive thinking depth. Default: `high`
`thinking`	object	No	Omit it to use default adaptive thinking, or use `{"type":"disabled"}` to turn thinking off.
`stream`	boolean	No	Enable SSE streaming. Default: `false`
`stop_sequences`	array	No	Sequences that stop generation

Claude Opus 5 uses adaptive thinking by default. max_tokens limits thinking and visible response tokens together, so use a sufficiently large value for xhigh and max workloads.

Manual extended thinking (thinking: {type: "enabled", budget_tokens: N}) and non-default temperature, top_p, or top_k values return a 400 error. Disabling thinking with thinking: {type: "disabled"} is supported only at low, medium, or high effort; combining it with xhigh or max also returns a 400 error.

API Reference

View the interactive API playground for Claude Opus 5.

Getting started

Model Introduction

Resources

Key capabilities

Quick example

Parameters

API Reference

​Key capabilities

​Quick example

​Parameters

API Reference

Key capabilities

Quick example

Parameters