gojev

Go harness for System One decision models: TypeSafe's hosted Jev and the open-weight, self-hostable Kev.

Decision models do not generate text. They take a state (a string or structured JSON) plus a map of typed questions and return one calibrated answer per question in a single forward pass.

Primitive	Ask	Get
Bool	yes/no	probability of yes
Choice	pick one of up to 255 options	chosen option + probability per option
Score	rate on an ordered rubric (2-10 levels)	interpolated score + probability per level

Where things live

The protocol layer is in the taigrr forks of fantasy and catwalk:

• fantasy.EvaluationModel / fantasy.EvaluationProvider — the modality abstraction.
• fantasy/providers/vercel — Vercel AI Gateway POST /v1/evaluate (model typesafe-ai/jev).
• fantasy/providers/typesafe — native POST /v1/systemone on api.typesafe.ai, or any wire-compatible server such as a local Kev.
• fantasy/providers/kev — Kev fully in-process (llama.cpp via yzma), weights downloaded at runtime.
• catwalk.Provider.EvaluationModels — Jev listed under the vercel and typesafe providers.

gojev adds what an agent framework needs on top: catwalk-driven construction, typed decision helpers, the Kev conversion tooling, and a CLI.

Install

go get github.com/taigrr/gojev

Usage

import (
    "github.com/taigrr/fantasy"
    "github.com/taigrr/fantasy/providers/vercel"
    "github.com/taigrr/gojev"
)

provider, _ := vercel.New(vercel.WithAPIKey(os.Getenv("AI_GATEWAY_API_KEY")))
model, _ := provider.(fantasy.EvaluationProvider).EvaluationModel(ctx, vercel.ModelJev)

resp, err := gojev.Evaluate(ctx, model, "Shoes arrived two weeks late and I see two charges on my card.", gojev.Questions{
    "department": gojev.Choice("Which team should handle this?", map[string]string{
        "returns":  "Exchanges, refunds, wrong or damaged items",
        "shipping": "Delivery status, delays, lost packages",
        "billing":  "Charges, invoices, payment problems",
    }),
    "escalate":    gojev.Bool("Does this need urgent human attention?"),
    "frustration": gojev.Score("How frustrated is the customer?", "Calm", "Frustrated", "Very angry"),
})

resp.Answers["department"].Choice   // "billing"
resp.Answers["escalate"].Yes()      // true
resp.Answers["frustration"].Level() // "Frustrated"

Typed decisions for gating

type Verdict string
const (Allow Verdict = "allow"; Ask Verdict = "ask"; Deny Verdict = "deny")

d, err := gojev.Classify(ctx, model, toolCall, "Should this run without asking?",
    []Verdict{Allow, Ask, Deny}, map[Verdict]string{Allow: "safe and reversible"})
if v, ok := d.Above(0.8, 0.3); ok && v == Allow { ... } // confident AND unambiguous

Also: gojev.AskBool(ctx, model, state, q).Above(threshold), gojev.Rate(...), gojev.Ask(...), gojev.Fallback(cloud, localKev).

From catwalk

model, err := gojev.FromCatwalk(ctx, provider, "") // uses provider.DefaultEvaluationModelID

Works for catwalk entries of type vercel and typesafe; $ENV API keys are resolved.

Local Kev, in-process

fantasy/providers/kev runs Kev entirely inside your process via llama.cpp (yzma, no cgo). Nothing is embedded in binaries; weights and the llama.cpp shared libraries are fetched on first use and cached under $KEV_CACHE (default: the OS cache dir, kev/).

p, _ := kev.New(
    kev.WithCheckpoint(kev.Checkpoint4B), // 0.8B fast on CPU; 4B default; 9B most accurate
    kev.WithAutoLibraries(),              // install pinned, verified llama.cpp if missing
)
defer p.(io.Closer).Close()
model, _ := p.(fantasy.EvaluationProvider).EvaluationModel(ctx, "") // free; loads on first Evaluate

Trust model

Everything that is downloaded is verified against a digest compiled into the Go module before it is written, loaded or executed:

• Weights: manifestDigests pins the SHA-256 of each checkpoint's manifest.json; every file in the bundle is then verified against that manifest. Corrupt or tampered files are re-fetched; an untrusted manifest is ErrManifestUntrusted.
• llama.cpp: LlamaCPPVersion pins the release and the SHA-256 of its digest manifest (the same pin yzma ships). Every archive and every extracted file is verified against it. On every load the installed files are re-hashed; a tampered library is ErrLibrariesCorrupt and is never dlopened.
• Upgrades: bumping LlamaCPPVersion makes existing installs report ErrLibrariesOutdated; with WithAutoLibraries() the new release is staged, verified, and swapped in atomically, then the old one removed.

Backend selection is automatic (Metal on Apple Silicon; CUDA → ROCm → Vulkan → CPU elsewhere) and can be forced with WithProcessor or $KEV_PROCESSOR.

Latency (M4 Max, f16, model loaded)

Checkpoint	1 q, short state	3 q, ~100 tok	8 q, ~100 tok	1 q, ~1500 tok	3 q, ~1500 tok
kev-0.8b (Metal)	14 ms	61 ms	130 ms	194 ms	250 ms
kev-4b (Metal)	45 ms	205 ms	423 ms	1.2 s	1.4 s
kev-9b (Metal)	68 ms	323 ms	800 ms	2.6 s	2.6 s
kev-0.8b (CPU, 12P+4E)	117 ms	460 ms	—	1.2 s	—
kev-4b (CPU)	630 ms	2.2 s	—	5.7 s	—
kev-9b (CPU)	1.1 s	—	—	—	—

Multiple questions share one decode of the state (KV prefix cache), so cost grows with branch tokens, not state × questions. On CPU-only machines prefer kev-0.8b; a Q8_0 4B bundle would roughly halve the 4B CPU numbers and is a convert.py --outtype q8_0 away.

Output matches Kev's Python server to two decimals on every fixture for all three checkpoints (tools/kev-convert). A running kev.serve (Python) is still reachable through fantasy/providers/typesafe with WithBaseURL("http://127.0.0.1:8008").

CLI

go run ./cmd/gojev -provider vercel \
  -state "rm -rf ./build && git push --force origin main" \
  -q "verdict=choice:Allow without asking?;allow=safe,ask=needs confirmation,deny=never" \
  -q "destructive=bool:Could this cause irreversible data loss?" \
  -q "risk=score:How risky?;harmless,moderate,dangerous"

-provider typesafe|vercel|kev|kev-server, -model picks the Kev checkpoint, -state - reads stdin, -json-state sends structured state, -json prints the raw response, -zdr requests zero data retention (Pro/Enterprise gateway plans only).

Development

go test ./...
staticcheck ./...

License

0BSD