# GLM 5.3 - Core.Today AI API

> Z.ai's GLM 5.3 served through the OpenRouter aggregator (listed 2026-08-18) - a large-scale text reasoning model built for complex software engineering and long-horizon agent tasks, and the successor to GLM 5.2. 1.31M-token context window, billed at OpenRouter's actual usage cost.

- **Provider**: Z.ai
- **Model ID**: z-ai/glm-5.3
- **Category**: LLM
- **Credits**: 5.4 per 1K tokens (avg, estimate)
- **Speed**: Medium
- **Quality**: Ultra

## Model Specifications
- **Context Window**: 1.3M tokens
- **Max Output**: 944K tokens
- **Training Cutoff**: Not published
- **Supported Formats**: text, json, markdown
- **Compatible SDK**: OpenAI

### Capabilities
- Function Calling
- Streaming
- JSON Mode
- System Prompt

### Token Pricing (per 1M tokens)
- **Input Tokens**: 2,601.2 credits ($1.73)
- **Output Tokens**: 8,175.2 credits ($5.45)
- **Cached Tokens**: 483.08 credits ($0.32)

## Features
- 1.31M-token context window (1M via the top provider), very large output budget
- Large-scale reasoning model (reasoning_effort + parallel tool calls)
- Text-only input and output
- OpenAI-compatible API (chat completions) via /llm/openrouter/v1
- Billed at OpenRouter's actual usage.cost - listed rates are estimates

## Use Cases
- Complex software engineering across large codebases
- Long-horizon agent workflows with tool use
- Reasoning-heavy analysis over very long inputs

## API Endpoint

Base URL: https://api.core.today
Endpoint: POST /llm/openrouter/v1/chat/completions

## Authentication
Header: Authorization: Bearer YOUR_API_KEY

Note: LLM endpoints use OpenAI-compatible format with Authorization Bearer token.

## Input Parameters

### Required
- **model**: string - Model ID in vendor/model form, e.g. "z-ai/glm-5.3".
- **messages**: array - Chat messages in OpenAI format (system/user/assistant roles).

### Optional
- **temperature**: number (default: 0.7) - Sampling temperature (0-2).
- **max_tokens**: integer (default: 2048) - Maximum completion tokens.
- **stream**: boolean (default: false) - Stream the response as server-sent events.

## Examples

### Chat completion
OpenAI-compatible chat completion request via OpenRouter
```json
{
  "model": "z-ai/glm-5.3",
  "messages": [
    {
      "role": "user",
      "content": "Summarize the attached report in 5 bullets."
    }
  ],
  "max_tokens": 1024
}
```

## Response Format
```json
{
  "id": "chatcmpl-abc123",
  "object": "chat.completion",
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "Response text here"
      },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 100,
    "completion_tokens": 50,
    "total_tokens": 150
  }
}
```

## Tips
- Works with the OpenAI SDK - set base_url to https://ai.api.core.today/llm/openrouter/v1
- Charged at OpenRouter's usage.cost x 1,858 credits/USD - the listed rates are estimates and may lag OpenRouter price changes
- Text-only - it does not accept images; for reasoning tasks use reasoning_effort to trade latency for depth, and enable parallel_tool_calls in agent loops

## Documentation
https://openrouter.ai/z-ai/glm-5.3