# Span-01 Lite

> Span-01 Lite is a behavior-scoring classifier from Respan — the free, lighter tier of Span-01, a 4B model trained with RLAIF on classification reasoning rather than fixed taxonomies. Send a conversation span and a set of plain-language behavior definitions and get a present / absent / not_observable probability per behavior in a single forward pass, with no token-by-token generation. Respan reports it ahead of Jev 1.13 and Sonnet 5 on their English and multilingual behavior-detection suites. Call POST /api/v1/decisions (POST /api/v1/systemone is the same handler).

**ID**: `respan/span-01-lite`  
**Creator**: respan  
**Category**: text  
**Context**: 0 tokens  
**Input**: $0  
**Output**: $0  
**Released**: 2026-09-26  
**Web page**: https://anyrouter.dev/model/respan/span-01-lite

**Input modalities**: text  
**Output modalities**: text  

**Capabilities**: systemone

**Supported parameters**: state, model, questions

**Aliases**: `respan/span-01-lite:free`

## Usage

**Endpoint**: `POST https://anyrouter.dev/api/v1/decisions`

```bash
curl https://anyrouter.dev/api/v1/decisions \
  -H "Authorization: Bearer $ANYROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "state": "Help! My payouts have been failing for 3 days.",
  "model": "respan/span-01-lite",
  "questions": {
    "is_urgent": {
      "type": "noul",
      "instructions": "Does this convey urgency?"
    }
  }
}'
```

Decisions is not chat: send `state` and typed `questions` (noul / choice / score). Requires a BYOK key for TypeSafe, LLM Gateway, Vercel AI Gateway, AIHubMix, AutoJev, or Fastino.

## Providers

| Provider | Input | Output |
| --- | --- | --- |
| openrouter-byok | $0 | $0 |

## Source

- Upstream docs: https://openrouter.ai/respan/span-01-lite