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Jev vs Kev on Opper
Opper hosts Kev 4B and typesafe/jev-latest on the same /v1/systemone compat route and compares accuracy, tokens, and latency on 362 post-release questions.
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- Last verified
- Sep 2026
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Highlights
- 362 questions written after both models shipped. Accuracies land within 2 points on every task.
- Same list price, but Jev adds about 257 fixed input tokens per request in their accounting.
- Through Opper, Kev answered in about 220 ms and Jev in about 275 ms.
- Swap model name between opper/kev-4b and typesafe/jev-latest; wire format unchanged.
Watch out
Opper's EU-hosted test. Sample size is modest; the post calls gaps inside the noise.
Questions about this entry
Short answers drawn from the linked project or page.
Opper's, and they both host the open model in the EU and resell the hosted one on one compat endpoint. The method is disclosed with frozen items and a fixed seed, but accuracy counts the top answer with yes/no cut at 0.5, a choice that flipped at least one item.
Because the open model was trained on them. The post lists AG News, Banking77, BoolQ, MNLI, SST-5, Yelp, IMDb, Amazon reviews, DBpedia, TREC, ARC, OpenBookQA and CommonsenseQA, and says it matched or beat the hosted model on most.
Token accounting. The post says the hosted model adds a fixed roughly 257 input tokens to every request at the same list price, which on the arXiv task works out to about $0.030 against $0.015 per 1,000 calls.
The post says no, calling it inside the noise for 362 items. It does report lower calibration error for the hosted model on the arXiv task, 0.032 against 0.044, which is a separate claim from raw accuracy.
It is a fine-tune by Jared Palmer of Alibaba's Qwen3.5-4B-Base with a small head that reads the answer from a single forward pass. It is Apache-2.0, returns a probability for every option, and Opper hosts it in the EU.
From text published after 2026-09-20 that neither model could have seen: newest arXiv papers in 8 categories, newest Stack Exchange questions on 6 sites, and new GitHub issues in six repositories. Categories and sites were balanced, the set frozen with a fixed seed, and ground truth comes from the source, never a model.
Send the same body to POST /v3/compat/v1/systemone and change only the model field between opper/kev-4b and typesafe/jev-latest. Kev speaks the same wire format, so the request, response shape, probabilities, and per-call cost header all stay identical.
Reactions & coverage
Posts, threads, and videos about this entry from around the web.
Hacker News: Opper hosts Kev 4B and typesafe/jev-latest on one systemone compat route.
felix08912 pointsJev vs. Kev: open-source Jev alternative tested side by sideRead the thread on Hacker NewsLinkedIn: What multimodal decision models actually change, and what they do not.
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Hacker News: Decision Index 0.2.1 scores open reproductions of Jev on a frozen suite.
jackbravo4 pointsDecision Index 0.2.1 – 70 open reproductions of TypeSafe Jev's Decision ModelRead the thread on Hacker NewsHacker News: Pointer to a DiffusionGemma plus vLLM tutorial for a Jev-shaped classifier.
1 pointHow to build a Jev-style classifier with DiffusionGemma and vLLMRead the thread on Hacker NewsMore Jev resources like this
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