Skip to main content

​
Overview

Some models generate a separate reasoning stream (sometimes called thinking) in addition to the final answer content. NanoGPT exposes this in an OpenAI-compatible way for Chat Completions:
  • Streaming (SSE): choices[0].delta.reasoning (or legacy choices[0].delta.reasoning_content)
  • Non-streaming: choices[0].message.reasoning (or legacy choices[0].message.reasoning_content)
Not every model exposes reasoning text. If a model does not emit a reasoning stream, these fields may be absent even if the model internally “reasons”.

​
Endpoint Variants (Chat Completions)

NanoGPT provides three base paths for chat completions. All accept the same request format and model names, but differ in how reasoning content is delivered:
Base URLBehaviorUse When
/api/v1/chat/completionsReasoning and answer are separate fields (reasoning + content).Most OpenAI-compatible clients
/api/v1legacy/chat/completionsSame as /api/v1/, but uses the legacy field name reasoning_content.Clients that only parse reasoning_content
/api/v1thinking/chat/completionsReasoning and answer are merged into the normal content stream.Clients that ignore reasoning fields but should still display thoughts
This is the same behavior documented under Reasoning Streams on the Chat Completion page.

​
Controlling Reasoning Output

​
Hide Reasoning

To strip reasoning from the response (both streaming and non-streaming), send: 
{
  "reasoning": { "exclude": true }
}
Or append the model suffix:
  • :reasoning-exclude
Example: 
{
  "model": "anthropic/claude-opus-4.5:reasoning-exclude",
  "messages": [{ "role": "user", "content": "What is 2+2?" }]
}

​
Reasoning Effort

For reasoning-capable models, you can ask for lighter/heavier reasoning: 
{
  "reasoning_effort": "high"
}
Or: 
{
  "reasoning": { "effort": "high" }
}
Valid values are none, minimal, low, medium, high.

​
Legacy Field Name Compatibility (reasoning_content)

If a client expects reasoning_content instead of reasoning, you can:
  1. Use /api/v1legacy/chat/completions, or
  2. Set reasoning.delta_field: "reasoning_content", or
  3. Use the shorthands reasoning_delta_field / reasoning_content_compat.

​
How Reasoning Appears in Responses

​
Streaming (SSE)

Reasoning deltas appear before or alongside content deltas: 
data: {"choices":[{"index":0,"delta":{"reasoning":"Thinking..."},"finish_reason":null}]}

data: {"choices":[{"index":0,"delta":{"content":"Here is the answer."},"finish_reason":null}]}

​
Non-Streaming

The final message may include a separate reasoning field: 
{
  "choices": [
    {
      "message": {
        "role": "assistant",
        "content": "Here is the answer.",
        "reasoning": "Thinking..."
      }
    }
  ]
}

​
Cost Notes

Reasoning tokens are billed as output tokens. If you enable higher reasoning effort (or use thinking variants), expect higher completion_tokens and higher cost.

​
See Also