TypeSafe Jev is the hosted model that introduced System One models on September 15, 2026: you send a state and typed questions, and it returns answers with probabilities instead of generated text. It is in early access and billed per token (third-party write-ups cite $0.042 per million input tokens).
Within days, open-source Jev alternatives appeared that do the same job on your own hardware. This post lists the ones worth testing, which of them accept Jev API requests unchanged, and what it takes to self-host one.
If you already call Jev, start with a model that serves the same POST /v1/systemone endpoint, so existing client code only needs a new base URL:
| Model | Size | License | Serves the Jev API | Good first choice when |
|---|---|---|---|---|
| Laya | 322M / 421M | Apache 2.0 | Yes, through laya-serve | You want a small model that runs on CPU, or 100+ languages |
| Kev | 0.8B to 27B | Apache 2.0 | Yes, the TypeSafe SDK works unchanged | You have a GPU and want the closest drop-in |
| Decider | 2B / 4B / 35B MoE | Apache 2.0 | Yes | You serve with vLLM and want many-option choices |
| Von | 395M | Apache 2.0 | Yes | You need low latency on modest hardware |
| OpenThai-SystemOne | 0.8B | Apache 2.0 | Yes | Your input is Thai |
Other open options use their own APIs: Bespoke Nimble (9B), GLiNER2.5-Decide (340M), Together AI's Tev1-4B, and the training-free AnyJev and SemIf. See the full System One model comparison for all twelve.
These projects put a Jev-style HTTP API in front of an open model, so you can switch models later without touching client code:
| Server | Language | Notes |
|---|---|---|
| laya-serve | Python | Ships with the upstream Laya package. See Self-host Laya . |
| Arbiter | Python | Routing, batching, metrics and a built-in playground |
| sys1 | Rust | candle-based, token batching, CPU, CUDA and Metal |
| ollaya | Rust | Ollama-style CLI and daemon; pulls models by name |
| laya-server | TypeScript | Docker image with a web console and API keys |
For the two Rust servers side by side, see Run Laya in Rust.
TYPESAFE_BASE_URL=http://localhost:11435. With plain HTTP, the request body stays the same:
curl -X POST http://localhost:8080/v1/systemone \
-H 'Content-Type: application/json' \
-d '{"state":{"message":"I was charged twice"},"questions":{"refund":{"type":"noul","instructions":"Does the customer ask for a refund?"}}}'
Hosted Jev still leads out of the box on several published comparisons, especially on tasks with many labels. On Banking77, with 77 intents, upstream Laya reports 0.425 at default settings against Jev's 0.870. Open models close much of the gap after fine-tuning on your own data, and they win on cost, privacy and latency when you run them close to your application. See Laya vs Jev for the details and caveats.
Benchmarks in this space are young and mostly self-reported on different datasets, so treat any single number as a starting point, not a verdict.
No. Jev's weights are not public. The Jev alternatives above are independent open models, mostly Apache 2.0, that answer the same kind of typed questions. Several of them also accept the same POST /v1/systemone requests.
The encoder models are the lightest: Laya (322M and 421M parameters), Von (395M) and GLiNER2.5-Decide (340M). See Laya on CPU for measured latency.
Yes, with a server that speaks the Jev API. Kev and ollaya say the SDK works unchanged, and laya-serve says an existing Jev client only needs a new base URL.
Last verified: September 25, 2026.
I maintain laya-ai.com, an independent Laya resource site; this article first appeared there as Jev alternatives. The site also keeps an auto-updated list of System One models on GitHub. It was drafted with AI assistance, and every fact was checked against the project pages linked above.