GLM 5.3 Flash API
AvailableGLM 5.3 Flash is the fast tier of Z.ai's GLM 5.3 family. It supports tool calling and structured JSON output and handles very long inputs, which makes it a good fit for agents and document workflows on a budget.
ChatReasoningTool callingJSON mode1M context
Context window
1M tokens
Modality
Text → Text
Input
$0.20 / 1M tokens
Output
$0.66 / 1M tokens
Time to first token
0.38 s
Output speed
265.6 tok/s
Model ID
zai-org/GLM-5.3-Flash
Quickstart
You need an API key to call this model. Create a free account or log in.
Set INFERENCE_API_KEY to your key from the API Keys page, then run:
curl https://api.inferenceapis.com/v1/chat/completions \
-H "Authorization: Bearer $INFERENCE_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "zai-org/GLM-5.3-Flash",
"messages": [
{"role": "system", "content": "You are a helpful assistant."},
{"role": "user", "content": "Hello! What can you do?"}
]
}'
import os
from openai import OpenAI
client = OpenAI(
base_url="https://api.inferenceapis.com/v1",
api_key=os.environ["INFERENCE_API_KEY"],
)
response = client.chat.completions.create(
model="zai-org/GLM-5.3-Flash",
messages=[
{"role": "system", "content": "You are a helpful assistant."},
{"role": "user", "content": "Hello! What can you do?"},
],
)
print(response.choices[0].message.content)
import OpenAI from "openai";
const client = new OpenAI({
baseURL: "https://api.inferenceapis.com/v1",
apiKey: process.env.INFERENCE_API_KEY,
});
const response = await client.chat.completions.create({
model: "zai-org/GLM-5.3-Flash",
messages: [
{ role: "system", content: "You are a helpful assistant." },
{ role: "user", content: "Hello! What can you do?" },
],
});
console.log(response.choices[0].message.content);
Endpoint
POST
https://api.inferenceapis.com/v1/chat/completions
Headers
Authorization: Bearer $INFERENCE_API_KEY
Content-Type: application/json
Content-Type: application/json
Compatible
OpenAI wire format.
/openai/v1/… is accepted too, so Groq-style base URLs work with only the host changed.
Model IDs and aliases
Send any of these as model; they all resolve to this model.
| ID | Note |
|---|---|
zai-org/GLM-5.3-Flash | Canonical |
glm-5.3-flash | Alias |
Request body
| Parameter | Type | Description |
|---|---|---|
model required |
string | Model ID: zai-org/GLM-5.3-Flash — also accepted: glm-5.3-flash |
messages required |
array | Conversation so far. Each item has a role (system, user or assistant) and content. |
max_tokens |
integer | Maximum number of tokens to generate (includes reasoning tokens — use a few hundred or more). |
temperature |
number | Sampling temperature. Higher values give more varied output. |
top_p |
number | Nucleus sampling cutoff. |
stream |
boolean | Stream the response as server-sent events. The final chunk includes usage. |
tools |
array | Tool definitions for function calling (OpenAI format). |
response_format |
object | {"type": "json_object"} for JSON mode. |
stop |
string | array | Sequences where the model stops generating. |
seed |
integer | Seed for more reproducible sampling. |
Response
200 OK · application/json
{
"id": "chatcmpl-abc123",
"object": "chat.completion",
"model": "zai-org/GLM-5.3-Flash",
"choices": [
{
"index": 0,
"message": {
"role": "assistant",
"content": "Hi! I can answer questions, write and edit text, help with code and more.",
"reasoning": "The user is greeting me and asking about capabilities..."
},
"finish_reason": "stop"
}
],
"usage": { "prompt_tokens": 28, "completion_tokens": 17, "total_tokens": 45 }
}
Pricing
| Input | $0.20 / 1M tokens |
| Output | $0.66 / 1M tokens |
| Billing | Pay as you go from prepaid credits. No subscription, no daily request or token cap. See all pricing. |
Notes
- Reasoning model — allow enough
max_tokensfor both thinking and the answer.
Compare GLM 5.3 Flash with…
Errors
Errors use the OpenAI envelope: {"error": {"message", "type", "code"}}. 401 missing or invalid key · 402 insufficient_balance · 404 model_not_found · 503 model_unavailable. See the error reference and provider error guides.
