# SignalHarness Model Output Regression Compare

> SignalHarness Model Output Regression Compare is a paid API for AI agents from signalharness.ai, paid per call via x402, $0.025/call, status unknown (last checked 2026-09-15).

Compares model outputs to detect regressions or differences between versions using caller-supplied data

## Facts

- Endpoint: POST https://signalharness.ai/api/agent/services/model_output_regression_compare/invoke
- Price: $0.025/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/signalharness-model-output-regression-compare-6d4b0115
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_TZpFKBwLqKCFeE10ILZHD

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability signalharness-model-output-regression-compare-6d4b0115 -d '<json body>'
```

Example prompt: Compare these two sets of model outputs and tell me if there's a regression — here's the JSON with my baseline predictions and the new model's predictions: {"baseline": [...], "candidate": [...]}

## When to prefer this

Choose this endpoint when you need a pay-per-call, agent-native regression comparison for AI model outputs — particularly when you want an auditable receipt on Base blockchain and are operating in an x402 micropayment environment. Prefer it over custom scripts when you need on-demand, stateless model output comparison without standing up MLOps infrastructure, and when cost-per-call billing ($0.025 USDC) is preferable to subscription pricing.

## Known failure modes

- Invalid or malformed request_json payload returns validation error
- request_json exceeding 65536 characters is rejected
- Empty or too-short input (below 2 chars) is rejected
- Caller-supplied data that doesn't match expected comparison schema may yield unreliable analysis with warnings
- Payment failure on x402 protocol results in 402 response before execution
- Network errors on Base chain may delay receipt settlement

## How this service works

Explore 330 pay-per-call x402 API services and 27 agent-native digital products, with Base USDC pricing, secure Polar checkout, and free discovery.

## Output

Returns a JSON analysis result containing a comparison of model outputs, any detected regressions or anomalies, warnings about data reliability (since inputs are caller-supplied), an evidence scope label, and a signed receipt with payment details, request/execution IDs, result SHA256 hash, and service metadata for auditability.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "request_json": {
   "type": "string",
   "maxLength": 65536,
   "minLength": 2
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "replay": false,
  "result": {
   "warnings": [
    "Verify the caller-supplied data before relying on this result."
   ],
   "service_id": "model_output_regression_compare",
   "analysis_json": "{\"example\":\"schema-valid caller-supplied data\"}",
   "evidence_scope": "caller_supplied_data"
  },
  "status": "succeeded",
  "receipt": {
   "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
   "usage": [],
   "status": "succeeded",
   "network": "eip155:8453",
   "artifacts": [],
   "endedAtMs": 0,
   "latencyMs": 0,
   "paymentId": "example-payment",
   "receiptId": "example-receipt",
   "requestId": "example-request",
   "serviceId": "model_output_regression_compare",
   "executionId": "example-execution",
   "startedAtMs": 0,
   "amountAtomic": "25000",
   "resultSha256": "61a816840107ad35a33c2014e6edfdef89b25d8dfb5d98573376bf5e8c0cbb36",
   "serviceVersion": "1.0.0",
   "settlementReference": "0x0000000000000000000000000000000000000000000000000000000000000000"
  },
  "artifacts": [],
  "requestId": "example-request",
  "executionId": "example-execution"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/signalharness-model-output-regression-compare-6d4b0115/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from signalharness.ai](https://www.zero.xyz/host/signalharness.ai/llms.txt)