[WhitneyLand]

StepFun is an interesting model.

If you haven’t heard of it yet there’s some good discussion here: https://news.ycombinator.com/item?id=47069179

[tarruda]

Since that discussion, they released the base model and a midtrain checkpoint:

- https://huggingface.co/stepfun-ai/Step-3.5-Flash-Base

- https://huggingface.co/stepfun-ai/Step-3.5-Flash-Base-Midtra...

I'm not aware of other AI labs that released base checkpoint for models in this size class. Qwen released some base models for 3.5, but the biggest one is the 35B checkpoint.

They also released the entire training pipeline:

- https://huggingface.co/datasets/stepfun-ai/Step-3.5-Flash-SF...

- https://github.com/stepfun-ai/SteptronOss

[lostmsu]

Tuned Qwen 3.5 27B beats Step 3.5 on almost all benchmarks, so the point about the size class is moot.

[tempaccount420]

Benchmarks are not interesting in deciding the "size class". Bigger size means more knowledge. Also, the Qwen 3.5 27B is a dense 27B active parameter model. StepFun 3.5 Flash has 11B active parameters.

[lostmsu]

> Bigger size means more knowledge.

Qwen 3.5 27B beats StepFun 3.5 Flash on GPQA Diamond too, so probably no.

[tarruda]

Benchmarks don't tell the whole story. For one-shot coding tasks, I found Step 3.5 Flash to be stronger even than Qwen 3.5 397B.

[anentropic]

Benchmarks don't tell the whole story... for that you need anecdotes from random HN posters :)

[skysniper]

thanks for the info. before running the bench i only tried it in arena.ai type of tasks and it was not impressive. i didn't expect it to be that good at agentic tasks