Extended Thinking (Reasoning)

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”. :thinking is model-specific and only works when that exact ID (or a documented alias) exists. -thinking is a legacy alias pattern for some model families only, not universal. Do not assume -thinking works for arbitrary model IDs. Always check GET /api/v1/models for exact valid IDs.

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 URL	Behavior	Use When
`/api/v1/chat/completions`	Reasoning and answer are separate fields (`reasoning` + `content`).	Most OpenAI-compatible clients
`/api/v1legacy/chat/completions`	Same as `/api/v1/`, but uses the legacy field name `reasoning_content`.	Clients that only parse `reasoning_content`
`/api/v1thinking/chat/completions`	Reasoning 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 }
}

reasoning.exclude controls output visibility. It is not the same as disabling reasoning compute. Or append the model suffix:

:reasoning-exclude

Example:

{
  "model": "anthropic/claude-opus-4.6:reasoning-exclude",
  "messages": [{ "role": "user", "content": "What is 2+2?" }]
}

Reasoning Effort

reasoning_effort (or reasoning.effort) controls reasoning depth and also acts as an explicit reasoning-mode signal. Any value other than none is treated as a request to enable reasoning/thinking behavior. Use none to explicitly disable reasoning behavior.

{
  "reasoning_effort": "high"
}

Or:

{
  "reasoning": { "effort": "high" }
}

Both formats are accepted. If both are present, top-level reasoning_effort is authoritative for Chat Completions request shaping. Valid values are none, minimal, low, medium, high, xhigh.

Legacy Field Name Compatibility (`reasoning_content`)

If a client expects reasoning_content instead of reasoning, you can:

Use /api/v1legacy/chat/completions, or
Set reasoning.delta_field: "reasoning_content", or
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.

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Endpoint Examples

API Reference

Miscellaneous

Partner

Integrations

Overview

Endpoint Variants (Chat Completions)

Controlling Reasoning Output

Hide Reasoning

Reasoning Effort

Legacy Field Name Compatibility (`reasoning_content`)

How Reasoning Appears in Responses

Streaming (SSE)

Non-Streaming

Cost Notes

See Also

​Overview

​Endpoint Variants (Chat Completions)

​Controlling Reasoning Output

​Hide Reasoning

​Reasoning Effort

​Legacy Field Name Compatibility (reasoning_content)

​How Reasoning Appears in Responses

​Streaming (SSE)

​Non-Streaming

​Cost Notes

​See Also

Overview

Endpoint Variants (Chat Completions)

Controlling Reasoning Output

Hide Reasoning

Reasoning Effort

Legacy Field Name Compatibility (`reasoning_content`)

How Reasoning Appears in Responses

Streaming (SSE)

Non-Streaming

Cost Notes

See Also