GLM-5.3-Flash

Text

Lower-cost GLM-5.3 tier; 1M context, always-on thinking; text requests through OpenAI and Anthropic SDKs

Input $0.12 / 1M tokens | Output $0.40 / 1M tokens GLM-5.3-Flash API reference →

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runapi.ai

# Base URL
https://runapi.ai

# Endpoints
POST /v1/chat/completions
POST /v1/responses
POST /v1/messages
POST /v1beta/models/glm-5.3-flash:generateContent
POST /v1beta/models/glm-5.3-flash:streamGenerateContent

curl https://runapi.ai/v1/chat/completions \
  -H "Authorization: Bearer $RUNAPI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "model": "glm-5.3-flash",
  "messages": [
    {
      "role": "user",
      "content": "Read this multi-file repository, find the failing integration test, and propose a patch with an explanation of the root cause."
    }
  ]
}'

from openai import OpenAI

client = OpenAI(
    base_url="https://runapi.ai/v1",
    api_key="your-runapi-key"
)

response = client.chat.completions.create(
    model="glm-5.3-flash",
    messages=[{"role": "user", "content": "Read this multi-file repository, find the failing integration test, and propose a patch with an explanation of the root cause."}]
)

import OpenAI from "openai";

const client = new OpenAI({
  baseURL: "https://runapi.ai/v1",
  apiKey: "your-runapi-key"
});

const response = await client.chat.completions.create({
  model: "glm-5.3-flash",
  messages: [{ role: "user", content: "Read this multi-file repository, find the failing integration test, and propose a patch with an explanation of the root cause." }]
});

https://runapi.ai 5 endpoints

10 versions available

OVERVIEW

What GLM-5.3-Flash is built for

GLM-5.3-Flash is the lower-cost model of Z.ai's GLM-5.3 generation, released on August 26, 2026. It is a Mixture-of-Experts model with 320B total parameters and 18B active per token. Z.ai describes it as the first open-source frontier model to combine sparse and linear attention, and reports about 3x less attention compute and a 4.4x smaller KV cache than GLM-5.3.

The context window is 1M tokens and output goes up to 128K tokens. Thinking is always on: Z.ai's API accepts only the enabled thinking mode, so every reply starts with a reasoning step. Z.ai aims the model at coding user interfaces from screenshots, office documents, financial research, and computer-use loops, and supports function calling and structured output.

Z.ai's model also reads images, video, and files. On RunAPI, glm-5.3-flash accepts text input only. Call it through the OpenAI-compatible Chat Completions endpoint (/v1/chat/completions), the Anthropic Messages endpoint (/v1/messages), OpenAI Responses, or Gemini generateContent, all with the same RunAPI API key.

Model ID

glm-5.3-flash

Released

August 26, 2026

Architecture

MoE, 320B total / 18B active

Context window

1M tokens

Max output

128K tokens

Thinking

Always on

Endpoint on RunAPI

OpenAI Chat Completions and Anthropic Messages, text input

Playground

Try GLM-5.3-Flash

Pick any model and generate in seconds.

Specifications

Provider	Z.ai
Model ID	glm-5.3-flash
Modality	Text
Task types	Synchronous
API endpoint	/v1/chat/completions
	/v1/responses

	/v1/messages
	/v1beta/models/glm-5.3-flash:generateContent
	/v1beta/models/glm-5.3-flash:streamGenerateContent
Billing unit	1K tokens
Catalog status	Operational

HOW IT WORKS

Use This Model in 3 Steps

Get Your Key

Sign up for free and create an API key for glm-5.3-flash from the dashboard.
Send a Request

POST to /v1/chat/completions with the glm-5.3-flash model slug and your parameters.
Get Results

Read the completed glm-5.3-flash response directly from the endpoint.

What this model offers

Endpoint coverage

Exposes 1 public endpoint(s): chat_completion.

Usage-based billing

Metered by 1K tokens with no subscription requirement.

GLM-5.3-Flash Pricing

Endpoint

Price

chat_completion

Input: $0.12 / 1M tokens Output: $0.40 / 1M tokens

Cache read: $0.03 / 1M tokens
Cache write 5m: Free / 1M tokens
Cache write 1h: Free / 1M tokens

API REFERENCE

Endpoint Specification

Endpoint: POST /v1/chat/completions
Model ID: glm-5.3-flash
Task Types: chat_completion

Request parameters

No request parameters are published for this endpoint.

USE CASES

Customer support

Answer customer questions from a private knowledge base, reducing ticket volume.

Document analysis

Draft contract summaries and flag key clauses for attorney review.

Code generation

Auto-generate unit tests, code reviews, and refactoring suggestions in CI.

FAQ

Frequently asked questions about GLM-5.3-Flash

How is GLM-5.3-Flash different from GLM-5.3?

GLM-5.3-Flash is the smaller, lower-cost model of the GLM-5.3 generation, with 320B total and 18B active parameters. Its hybrid sparse and linear attention cuts attention compute by about 3x against GLM-5.3, according to Z.ai. Both have a 1M-token context window. Choose glm-5.3 for the flagship model and glm-5.3-flash for high-volume or cost-sensitive work.

Can I turn thinking off on GLM-5.3-Flash?

No. Z.ai ships it with thinking always on, and the thinking setting accepts only enabled. Reasoning tokens count toward the output, so leave room for them in max_tokens.

Can I send images to glm-5.3-flash on RunAPI?

Not yet. Z.ai's model reads images, video, and files, but RunAPI accepts text input only for glm-5.3-flash, and requests with image parts are rejected.

Which SDKs can call glm-5.3-flash?

Point the OpenAI SDK at https://runapi.ai/v1 for Chat Completions or Responses, or use the Anthropic SDK for Messages, and set the model to glm-5.3-flash. One RunAPI API key works for every protocol.

How do I select glm-5.3-flash?

Pass the model ID shown in the quickstart.

What's the rate limit on this variant?

Per-key rate limits scale with your usage tier. The pricing page shows current limits. If you need higher throughput, contact support to discuss tier upgrades.

Can I switch variants later?

Yes. Variant is a parameter in the request. Switch by changing the model ID — no code changes, no re-authentication, no separate billing setup. All variants share the same API key and request shape.

Does it stream?

Where streaming is available, RunAPI streams end-to-end. LLM models support token-level streaming. Media models use async task polling or webhook callbacks for result delivery.

Where do I report quality issues?

Open an issue on the public GitHub repo or email support at [email protected]. Include the task ID and model ID so the team can investigate the specific generation.

Do I need a separate provider account?

No. Your RunAPI API key is enough to access this variant and every other model in the catalog. You do not need accounts with the underlying provider.

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