# GLM-5.3

> GLM-5.3 is a Z.ai flagship reasoning model for complex software engineering and long-horizon agent tasks.

## Key facts

- Model author: Z.ai
- Input: $1.1429 per 1M tokens (starting price)
- Output: $4.00 per 1M tokens (starting price)
- Cached input: $0.26 per 1M tokens
- Context window: 1,000,000 tokens
- Maximum output: 128,000 tokens
- Input modalities: text
- Output modalities: text
- Capabilities: reasoning, structured_output, tools
- Released: 2026-08-18
- Model IDs: `jd/glm-5.3`, `z-ai/glm-5.3`
- Model page: https://www.realrelay.ai/model/z-ai/glm-5.3

## Overview

GLM-5.3 is a large-scale reasoning model from Z.ai, positioned as its flagship and built for complex software engineering and long-horizon agent tasks. Z.ai lists coding capabilities and emerging cybersecurity capabilities among its strengths. Reasoning, tool calling and structured output are available for agents that work through a task step by step.

GLM-5.3 has a 1M-token context window and can generate up to 128K output tokens. It accepts text input and returns text output. It was released on August 18, 2026. Its weights are openly available.

## Capabilities

GLM-5.3 supports reasoning, structured output and tool calling. Z.ai describes it as stronger on long-horizon, complex tasks.

## Pricing

GLM-5.3 starts from $1.1429 per 1M input tokens and from $4.00 per 1M output tokens. Cache reads start from $0.26 per 1M tokens. These are starting prices and the rate can vary.

GLM-5.3 is available through RealRelay's OpenAI-compatible API.

## Use cases

Use GLM-5.3 for complex software engineering: multi-file changes, debugging and code review across a large repository held in its 1M-token context.

Long-horizon agents also fit well, because they can keep working through a plan across many steps. Z.ai also documents emerging cybersecurity capabilities, which teams can evaluate on security-related code tasks.

## Call it

OpenAI-compatible chat completions:

```bash
curl https://www.realrelay.ai/v1/chat/completions \
  -H "Authorization: Bearer $REALRELAY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "z-ai/glm-5.3", "messages": [{"role": "user", "content": "Hello"}]}'
```

## FAQ

### What is GLM-5.3?

GLM-5.3 is a Z.ai flagship reasoning model for complex software engineering and long-horizon agent tasks.

### How much does GLM-5.3 cost?

GLM-5.3 starts from $1.1429 per 1M input tokens and from $4.00 per 1M output tokens, with cache reads from $0.26 per 1M tokens.

### What is the context window of GLM-5.3?

GLM-5.3 has a 1M-token context window and can generate up to 128K output tokens.

### What inputs and outputs does GLM-5.3 support?

GLM-5.3 accepts text input and returns text output.

### Does GLM-5.3 support tool calling?

Yes. GLM-5.3 supports tool calling, along with reasoning and structured output.

### When was GLM-5.3 released?

GLM-5.3 was released on August 18, 2026.

### How do I call GLM-5.3 via the API?

Send requests to RealRelay's OpenAI-compatible API and use the model ID z-ai/glm-5.3.