Reasoning

LLMGateway supports reasoning-capable models that can show their step-by-step thought process before providing a final answer. This feature is particularly useful for complex problem-solving tasks, mathematical calculations, and logical reasoning.

Reasoning-Enabled Models

You can find all reasoning-enabled models on our models page with reasoning filter. These models include:

• OpenAI's GPT-5 series (e.g., gpt-5, gpt-5-mini)
  • Note: GPT-5 models use reasoning but currently do not return the reasoning content in the response.
• Anthropic's Claude 3.7 Sonnet
• Google's Gemini 2.0 Flash Thinking and Gemini 2.5 Pro
• GPT OSS models such as gpt-oss-120b and gpt-oss-20b
• Z.AI's reasoning models

Using the Reasoning Parameter

To enable reasoning output, add the reasoning_effort parameter to your request. This parameter accepts the following values:

• minimal - Fastest reasoning with minimal thought process (only for GPT-5 models)
• low - Light reasoning for simpler tasks
• medium - Balanced reasoning for most tasks
• high - Deep reasoning for complex problems

Example Request

curl -X POST "https://api.llmgateway.io/v1/chat/completions" \
  -H "Authorization: Bearer $LLM_GATEWAY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5-preview",
    "messages": [
      {
        "role": "user",
        "content": "What is 2/3 + 1/4 + 5/6?"
      }
    ],
    "reasoning_effort": "medium"
  }'

Example Response

The response will include a reasoning field in the message object containing the model's step-by-step thought process:

{
	"id": "chatcmpl-abc123",
	"object": "chat.completion",
	"created": 1234567890,
	"model": "gpt-5-preview",
	"choices": [
		{
			"index": 0,
			"message": {
				"role": "assistant",
				"content": "The answer is 1.75 or 7/4.",
				"reasoning": "First, I need to find a common denominator for 2/3, 1/4, and 5/6. The LCD is 12. Converting: 2/3 = 8/12, 1/4 = 3/12, 5/6 = 10/12. Adding: 8/12 + 3/12 + 10/12 = 21/12 = 1.75 or 7/4."
			},
			"finish_reason": "completed"
		}
	],
	"usage": {
		"prompt_tokens": 20,
		"completion_tokens": 45,
		"reasoning_tokens": 35,
		"total_tokens": 65
	}
}

Streaming Reasoning Content

When streaming is enabled, reasoning content will be streamed as part of the response chunks:

curl -X POST "https://api.llmgateway.io/v1/chat/completions" \
  -H "Authorization: Bearer $LLM_GATEWAY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5-preview",
    "messages": [
      {
        "role": "user",
        "content": "Solve this logic puzzle: If all roses are flowers and some flowers fade quickly, can we conclude that some roses fade quickly?"
      }
    ],
    "reasoning_effort": "high",
    "stream": true
  }'

The reasoning content will appear in the stream chunks before the final answer, allowing you to display the model's thought process in real-time.

Example:

data: {
	"id": "chatcmpl-fb266880-1016-4797-9a70-f21a538edaf6",
	"object": "chat.completion.chunk",
	"created": 1761048126,
	"model": "openai/gpt-oss-20b",
	"choices": [
		{
			"index": 0,
			"delta": {
				"reasoning": "It's ",
				"role": "assistant"
			},
			"finish_reason": null
		}
	]
}

Usage Tracking

Response Payload

The usage object in the response includes reasoning-specific token counts:

• reasoning_tokens - Number of tokens used for the reasoning process
• completion_tokens - Number of tokens in the final answer
• prompt_tokens - Number of tokens in the input
• total_tokens - Sum of all token counts

Logs and Analytics

All requests using the reasoning_effort parameter are tracked in your dashboard logs with:

• The reasoningContent field containing the full reasoning text
• Separate token counts for reasoning vs. completion
• Performance metrics for reasoning-enabled requests

You can view detailed logs for each request in the dashboard to analyze how models are reasoning through problems.

Auto-Routing with Reasoning

When using auto-routing (specifying a model like gpt-5 without a specific version), LLMGateway will:

1. Automatically set reasoning_effort to minimal for GPT-5 models
2. Set reasoning_effort to low for other auto-routed reasoning models
3. Only route to providers that support reasoning when reasoning_effort is specified

This ensures optimal performance and cost when using auto-routing with reasoning-capable models.

Model-Specific Behavior

Not all reasoning models return reasoning content in the same way. Some models (like OpenAI models) may reason internally but not expose the reasoning content in the response. LLMGateway makes sure the response is unified across different providers, but the depth and format of reasoning may vary.

Best Practices

1. Choose appropriate reasoning effort: Use low or minimal for simple tasks, medium for most tasks, and high only for complex problems that require deep reasoning
2. Monitor token usage: Reasoning can significantly increase token consumption - monitor your reasoning_tokens in the usage object
3. Stream for better UX: When building user-facing applications, enable streaming to show the reasoning process in real-time
4. Check logs: Review the reasoningContent in your dashboard logs to understand how models are solving problems

Error Handling

If you specify reasoning_effort for a model that doesn't support reasoning, you'll receive an error:

{
	"error": {
		"message": "Model gpt-4o does not support reasoning. Remove the reasoning_effort parameter or use a reasoning-capable model.",
		"type": "invalid_request_error",
		"code": "model_not_supported"
	}
}

To avoid this error, only use the reasoning_effort parameter with reasoning-enabled models.