Claude Opus 4.5

Text Generation • Anthropic

anthropic/claude-opus-4.5

• Third-party
• Zero data retention

Claude Opus 4.5 brings further reasoning, coding, and agentic improvements over Opus 4.1, with stronger tool use and tighter instruction following.

Usage

const response = await env.AI.run(
  'anthropic/claude-opus-4.5',
  {
    max_tokens: 1024,
    messages: [{ content: 'What are the three laws of thermodynamics?', role: 'user' }],
  },
)
console.log(response)

curl https://api.cloudflare.com/client/v4/accounts/$CLOUDFLARE_ACCOUNT_ID/ai/v1/messages \
  --header "Authorization: Bearer $CLOUDFLARE_API_TOKEN" \
  --header "Content-Type: application/json" \
  --data '{
  "model": "anthropic/claude-opus-4.5",
  "max_tokens": 1024,
  "messages": [
    {
      "content": "What are the three laws of thermodynamics?",
      "role": "user"
    }
  ]
}'

The three laws of thermodynamics are:

**First Law (Conservation of Energy):** Energy cannot be created or destroyed, only transferred or converted from one form to another. In a closed system, the change in internal energy equals heat added minus work done by the system.

**Second Law (Entropy):** In any natural process, the total entropy of an isolated system always increases or remains constant; it never decreases. Heat flows spontaneously from hot to cold, not the reverse. This also establishes that no heat engine can be 100% efficient.

**Third Law (Absolute Zero):** As temperature approaches absolute zero (0 Kelvin), the entropy of a perfect crystal approaches zero. It's impossible to reach absolute zero in a finite number of steps.

There's also sometimes a **Zeroth Law** mentioned, which states that if two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other—essentially establishing temperature as a transitive property.

{
  "content": [
    {
      "text": "The three laws of thermodynamics are:\n\n**First Law (Conservation of Energy):** Energy cannot be created or destroyed, only transferred or converted from one form to another. In a closed system, the change in internal energy equals heat added minus work done by the system.\n\n**Second Law (Entropy):** In any natural process, the total entropy of an isolated system always increases or remains constant; it never decreases. Heat flows spontaneously from hot to cold, not the reverse. This also establishes that no heat engine can be 100% efficient.\n\n**Third Law (Absolute Zero):** As temperature approaches absolute zero (0 Kelvin), the entropy of a perfect crystal approaches zero. It's impossible to reach absolute zero in a finite number of steps.\n\nThere's also sometimes a **Zeroth Law** mentioned, which states that if two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other—essentially establishing temperature as a transitive property.",
      "type": "text"
    }
  ],
  "gatewayMetadata": {
    "keySource": "BYOK"
  },
  "id": "msg_01KCBDSEEzS8kikdpAQHP1qf",
  "model": "claude-opus-4-5-20251101",
  "role": "assistant",
  "stop_details": null,
  "stop_reason": "end_turn",
  "stop_sequence": null,
  "type": "message",
  "usage": {
    "input_tokens": 17,
    "output_tokens": 215
  }
}

Examples

<details>

<summary>With System Message — Using a system message to set context</summary>

const response = await env.AI.run(
  'anthropic/claude-opus-4.5',
  {
    max_tokens: 1024,
    messages: [{ content: 'How do I read a JSON file in Python?', role: 'user' }],
    system: 'You are a helpful coding assistant specializing in Python.',
    temperature: 0.3,
  },
)
console.log(response)

curl https://api.cloudflare.com/client/v4/accounts/$CLOUDFLARE_ACCOUNT_ID/ai/v1/messages \
  --header "Authorization: Bearer $CLOUDFLARE_API_TOKEN" \
  --header "Content-Type: application/json" \
  --data '{
  "model": "anthropic/claude-opus-4.5",
  "max_tokens": 1024,
  "messages": [
    {
      "content": "How do I read a JSON file in Python?",
      "role": "user"
    }
  ],
  "system": "You are a helpful coding assistant specializing in Python.",
  "temperature": 0.3
}'

````

Reading JSON Files in Python

Python's built-in json module makes it easy to read JSON files.

Basic Example

```python import json