MiniMax-M3 emits answer tokens before closing </think> — answer truncated after stripping reasoning

[nelsonbarrac]

Summary

On the hosted OpenAI-compatible API (https://api.minimax.io/v1/chat/completions), MiniMax-M3 with thinking enabled intermittently emits the first tokens of the final answer before closing the </think> block. As a result, once the <think>...</think> block is stripped, the user-facing answer starts mid-sentence (its opening words are lost inside the reasoning block).

This is reproducible directly against the API, with no client framework involved, in both streaming and non-streaming modes. It is a property of the raw generation, not of any downstream parser.

Environment

• Model: MiniMax-M3
• Endpoint: https://api.minimax.io/v1/chat/completions (OpenAI-compatible)
• Thinking: enabled (default / adaptive)
• Reproduced with raw curl/fetch — no SDK, no LangChain, no vLLM.

Reproduction

curl -s https://api.minimax.io/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $MINIMAX_API_KEY" \
  -d '{
    "model": "MiniMax-M3",
    "messages": [{ "role": "user", "content": "Hola" }],
    "stream": false
  }'

Run it ~8 times. In roughly 25% of runs the returned content looks like:

<think>
...reasoning... I should respond in a friendly manner.¡Hola! 👋 ¿Cómo
</think>

estás? Soy un asistente de IA aquí para ayudarte. ¿En qué puedo ayudarte hoy?

Note that the greeting ¡Hola! 👋 ¿Cómo was emitted inside the <think> block, and the text after </think> starts mid-sentence with estás?.

Actual behavior

The closing </think> boundary is placed after the model has already started the final answer, so the answer's opening tokens are trapped inside the reasoning block. Stripping <think>...</think> (the documented handling for the OpenAI native format) yields a truncated answer.

Observed rate on the prompt "Hola", non-streaming: 2/8 hard truncations + 1 partial (missing the leading ¡).

Expected behavior

</think> should close before any final-answer token is emitted. Everything inside <think>...</think> should be reasoning only; the final answer should be fully contained in the post-</think> content.

reasoning_split=true does not fix it (and is worse)

Setting reasoning_split=true (so thinking is returned in reasoning_content / reasoning_details) exhibits the same boundary defect: the answer's opening tokens land in reasoning_content, and content starts mid-sentence. Reproduced non-streaming as well:

content:           "? Soy un asistente de IA y estoy aquí para ayudarte..."
reasoning_content: "...I should respond in a friendly manner...¡Hola! 👋 ¿Cómo estás"

Impact

Any integration that separates reasoning from the answer (the documented pattern) shows user-facing responses that begin mid-sentence. It affects real replies, not just greetings.

Notes

• M2.7 did not exhibit this in our testing.
• Related but distinct reports (parser leaking <mm:think> tags): vLLM #45687, #46042; Kilo-Org/kilocode #11203. This report is about the raw hosted-API generation placing the </think> boundary a few tokens into the answer.