Claude Opus 5 Migration Guide

// Chat Completions API
{
  "model": "anthropic/claude-opus-5",
  "reasoning": { "enabled": false },
  "messages": [{ "role": "user", "content": "Hello" }]
}

// Messages API
{
  "model": "anthropic/claude-opus-5",
  "thinking": { "type": "disabled" },
  "messages": [{ "role": "user", "content": "Hello" }]
}

// Chat Completions API — OK: disabled reasoning at high effort
{
  "model": "anthropic/claude-opus-5",
  "reasoning": { "enabled": false, "effort": "high" }
}

// Chat Completions API — 400 from Anthropic: xhigh requires reasoning
{
  "model": "anthropic/claude-opus-5",
  "reasoning": { "enabled": false, "effort": "xhigh" }
}

// Messages API
{
  "model": "anthropic/claude-opus-5",
  "max_tokens": 1024,
  "tools": [
    {
      "name": "get_weather",
      "description": "Get weather",
      "input_schema": { "type": "object", "properties": { "city": { "type": "string" } } }
    },
    {
      "name": "get_forecast",
      "description": "Get 5-day forecast",
      "input_schema": { "type": "object", "properties": { "city": { "type": "string" } } },
      "defer_loading": true
    }
  ],
  "messages": [
    { "role": "user", "content": "What tools do you have for weather in Paris?" },
    {
      "role": "system",
      "content": [
        { "type": "tool_addition", "tool": { "type": "tool_reference", "name": "get_forecast" } }
      ]
    }
  ]
}