/v1/chat/completions streams thinking into content instead of reasoning_content when no tools are requested

[luisi-tech]

May not be an issue for most and I’m not savvy enough to know if this would be the same for other chat hosts, but experienced this and asked Opus to summarize what it found when using ds4-server with openai:

Streaming chat requests without a tools field bypass the structured OpenAI streamer and fall through to the plain SSE path, which emits every token (including the literal closer) as content deltas. Reasoning never lands in reasoning_content, and clients like Jan that look for balanced ... tags see only the closer.

Repro:

curl -N http://127.0.0.1:8000/v1/chat/completions
-H 'Content-Type: application/json'
-d '{"model":"deepseek-v4-flash","messages":[{"role":"user","content":"What is 17 * 23?"}],"stream":true}'

Observed: every delta is {"content":"..."}, including one {"content":""} mid-stream.
Expected: thinking tokens in reasoning_content deltas, no literal on the wire.
Cause is in ds4_server.c around line 4964: structured_stream and openai_live_tools both require j->req.has_tools, so non-tool chats skip openai_sse_stream_update (which already handles thinking correctly) and use the plain sse_chunk path at line 5083. Dropping the has_tools requirement so the OpenAI structured streamer runs for all OpenAI streaming chats fixes it; verified locally against Jan.

[fry69]

I do not see this behavior, on my machine running current main, the response gets correctly split into reasoning_content and content delta parts.

Note that there were some recent fixes regarding ds4-server and reasoning token encapsulation, so make sure you run the latest commit.

Command:

curl -N http://127.0.0.1:8000/v1/chat/completions -H 'Content-Type: application/json' -d '{"model":"deepseek-v4-flash","messages":[{"role":"user","content":"What is 17 * 23?"}],"stream":true}'

Output:

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"role":"assistant"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"We "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"need to "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"c"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"om"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"pu"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"t"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"e "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"1"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"7 * 2"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"3. "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"Th"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"is is a straight"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"forward multipl"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"i"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"c"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"at"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"io"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"n"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":". "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"17"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"* 2"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258878,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"0"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" = 3"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"4"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"0,"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" a"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"n"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"d"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" 1"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"7"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" *"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"3 ="},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" 51, s"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"o"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" to"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"t"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"al 391. Altern"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"a"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"t"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"iv"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"e"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"ly"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":", "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"17"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"*2"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"3"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"= ("},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"20"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"-"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"3"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":")"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"*("},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"2"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"0+3"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":") "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"="},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258879,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"40"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"0"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" - "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"9"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" = "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"391. So"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" an"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"s"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"wer"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":" "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"reasoning_content":"is 391."},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"content":"17"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"content":" multiplied"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"content":" by"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"content":" "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"content":"23"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"content":" equals"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"content":" "},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"content":"391"},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{"content":"."},"finish_reason":null}]}

data: {"id":"chatcmpl-3","object":"chat.completion.chunk","created":1778258880,"model":"deepseek-v4-flash","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}

data: [DONE]

[luisi-tech]

Didn’t know there was an update, diffed against prior version, behavior was fixed in the update. Thanks!