# GLM 5.3 Flash - Core.Today AI API

> Z.ai's GLM 5.3 Flash served through the OpenRouter aggregator (listed 2026-08-26) - a low-cost native multimodal model (text, image, video input) for efficient coding and long-horizon agent tasks. Its hybrid sparse and linear attention keeps long-context behavior accurate across a 1.31M-token window. Billed at OpenRouter's actual usage cost.

- **Provider**: Z.ai
- **Model ID**: z-ai/glm-5.3-flash
- **Category**: LLM
- **Credits**: 0.6 per 1K tokens (avg, estimate)
- **Speed**: Fast
- **Quality**: High

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

### Capabilities
- Vision (image input)
- Function Calling
- Streaming
- JSON Mode
- System Prompt

### Token Pricing (per 1M tokens)
- **Input Tokens**: 278.7 credits ($0.19)
- **Output Tokens**: 929 credits ($0.62)
- **Cached Tokens**: 55.74 credits ($0.04)

## Features
- 1.31M-token context window (1M via the top provider), very large output budget
- Very low cost - budget-tier input and output rates
- Native multimodal input (text, image, video) with reasoning (reasoning_effort + parallel tool calls)
- OpenAI-compatible API (chat completions) via /llm/openrouter/v1
- Billed at OpenRouter's actual usage.cost - listed rates are estimates

## Use Cases
- High-volume coding assistance and agent loops
- Screenshot, image and video understanding in agents
- Cheap long-context 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-flash".
- **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-flash",
  "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
- Accepts image and video input in OpenAI content-part format; use reasoning_effort to trade latency for depth, and step up to z-ai/glm-5.3 for the hardest engineering tasks

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