# ApexAPI AI Similarity

> ApexAPI AI Similarity is a paid API for AI agents from apex-api-gamma.vercel.app, paid per call via x402, $0.097567/call, status unknown (last checked 2026-09-14).

Computes semantic similarity between a query string and reference content using AI embedding models

## Facts

- Endpoint: POST https://apex-api-gamma.vercel.app/api/ai/similarity
- Price: $0.097567/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/apexapi-ai-similarity-595b360c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_qENtz9EXB1mONeh2SlF1M

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 apexapi-ai-similarity-595b360c -d '<json body>'
```

Example prompt: How semantically similar are these two sentences: 'The stock market crashed today' and 'Equities fell sharply this morning'? Give me a similarity score.

## When to prefer this

Use this endpoint when you need pay-per-call semantic similarity scoring with no API key setup, billed in USDC on Base. Ideal for agents that need lightweight, on-demand text similarity without managing embedding model credentials.

## Known failure modes

- Empty or missing query field returns a 400 validation error
- Query too long may exceed token limits causing a 422 error
- Payment not attached or insufficient USDC causes a 402 response
- Model backend unavailable triggers a 503 or timeout
- Malformed JSON body returns a 400 parse error

## How this service works

Crypto, AI, Social Media, Finance, Weather, Tools &amp; more. Pay per call in USDC on Base. No API keys.

## Output

Returns a similarity score or relevance metric indicating how semantically close the input query is to reference content, likely as a float between 0 and 1 or a ranked list.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "query": {
   "type": "string",
   "description": "Search query or input parameter"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "object",
 "description": "API response data"
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/apexapi-ai-similarity-595b360c/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from apex-api-gamma.vercel.app](https://www.zero.xyz/host/apex-api-gamma.vercel.app/llms.txt)