AI Desk · AI FingerprintingNew arrival
Why high: an exact fingerprint shared with 13 models that declare the same family, without a second signal of a different kind yet.
StepFun: Step 5 Preview is StepFun's model. Its measured tokenizer sits with the DeepSeek group, which is evidence that it builds on the DeepSeek tokenizer. Tokenizer reuse is normal engineering, open vocabularies travel between labs, and this says nothing against StepFun's authorship of the model itself.
Measured on 8 October 2026. Step 5 Preview counts tokens exactly as DeepSeek V4 Pro, V4 Flash and the rest of DeepSeek's current line do on all 50 strings, as StepFun's Step 3.5 Flash and Step 3.7 Flash already did. StepFun's flagship keeps DeepSeek's vocabulary.
| We checked | What we found | Where it came from |
|---|---|---|
| How it counts tokens | Counts every one of the 50 test strings exactly like 13 other models | tk_73c4f0dc |
| How its API is set up | A combination of settings no other listing in the catalogue uses | api_50829359 |
| How much it can read and write | Reads up to 1,000,000 tokens at once, writes up to 64,000 | its own listing |
| Whether it thinks before answering | Always reasons, and cannot be turned off, at high, medium, low, medium by default | its own listing |
| Who served our requests | StepFun | we measured it, 8 October 2026 |
Click a row to open the full comparison.
We sent StepFun: Step 5 Preview fifty short pieces of text and recorded what each one cost it in tokens. The bars below are those costs. Two models built on the same tokenizer produce the same bars; a model built on a different one produces a different set, which is what makes this a fingerprint.
Overhead subtracted: 11 prompt tokens.
Step 5 Preview is StepFun's flagship model for agentic work, built on a sparse Mixture-of-Experts architecture (27B active / 600B total parameters). It performs strongly in software engineering and professional...
Supported parameters
frequency_penaltyinclude_reasoninglogprobsmax_tokensreasoningreasoning_effortresponse_formatstopstructured_outputstemperaturetoolstop_logprobstop_p
defaults: {"temperature":null,"top_p":null,"top_k":null,"frequency_penalty":null,"presence_penalty":null,"repetition_penalty":null}
