# GLM-5.3 Fast

GLM-5.3 Fast is a higher-throughput serving variant of Z.AI's GLM-5.3, using the same weights so output quality matches the standard endpoint. It targets agent loops that chain many model calls, keeping GLM-5.3's always-on thinking, reasoning-effort control, tool calling, and long-context inputs at faster speeds. Its published context window is 1,000,000 tokens. The advertised input rate is $2.10 per million input tokens. The advertised output rate is $6.60 per million output tokens.

- Model identifier: ` zai/glm-5.3-fast `
- Creator: Z.AI
- Providers: Fireworks
- Model type: Text generation
- Canonical model page: [GLM-5.3 Fast](<https://impossibl.com/zai/glm-5.3-fast>)
- API availability: Listed as serving through Impossibl.
- Creator release date: 2026-08-14

## Providers

Fireworks hosts GLM-5.3 Fast. Impossibl routes your request intelligently and handles failover automatically when a provider is down.

| Provider | Endpoint location | Routes | Verified context window | Tool calling |
| --- | --- | --- | --- | --- |
| Fireworks | Not specified | 1 | Not verified | Not verified |

The model price applies whichever provider serves the request. Endpoint locations do not guarantee inference residency.

## Specs and Capabilities

- Context window: 1,000,000 tokens
- Maximum output tokens: Not published in the public catalog; this is separate from the context window.
- Inputs: text
- Outputs: text
- Tool calling: Not published

## API access

Use ` zai/glm-5.3-fast ` as the model identifier through the Impossibl API.

Published API endpoints:

- ` /v1/chat/completions `

[API quickstart](<https://impossibl.com/docs/agent-quickstart>) · [Models and billing documentation](<https://impossibl.com/docs/models>)

## Published API prices

All rates are in USD. An unpublished rate is unknown, not zero. Workspace-specific pricing, taxes, balance-purchase fees, billing adjustments, and tool charges can affect the amount paid.

| Usage | Published base rate | Billing unit |
| --- | --- | --- |
| Input | $2.10 | per million input tokens |
| Output | $6.60 | per million output tokens |
| Cache read | $0.39 | per million cached input tokens |
| Cache write (default retention) | Not published | per million tokens |
| Cache write (one-hour retention) | Not published | per million tokens |
| Audio input | Not published | per million audio input tokens |

## Availability and retirement

The model is listed as serving. No retirement is announced in the current public catalog.

## Frequently asked questions

### What is GLM-5.3 Fast?

GLM-5.3 Fast is a higher-throughput serving variant of Z.AI's GLM-5.3, using the same weights so output quality matches the standard endpoint. It targets agent loops that chain many model calls, keeping GLM-5.3's always-on thinking, reasoning-effort control, tool calling, and long-context inputs at faster speeds.

Sources: [Fireworks serverless pricing](<https://docs.fireworks.ai/serverless/pricing>); [Z.AI release announcement](<https://z.ai/blog/glm-5.3>)

### How much does GLM-5.3 Fast cost?

GLM-5.3 Fast costs $2.10 per million input tokens and $6.60 per million output tokens through the Impossibl API. Cache reads cost $0.39 per million tokens. All rates are in USD.

### What is the context length of GLM-5.3 Fast?

GLM-5.3 Fast has a 1,000,000-token context window through the Impossibl API.

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

GLM-5.3 Fast accepts text as input. GLM-5.3 Fast returns text.

### How do I use GLM-5.3 Fast through an API?

GLM-5.3 Fast is available through the Impossibl API. Use zai/glm-5.3-fast as the model identifier with /v1/chat/completions. The quickstart explains how to create an API key and send your first request.

### When was GLM-5.3 Fast released?

Z.AI released GLM-5.3 Fast on August 14, 2026.

Sources: [Creator release announcement](<https://z.ai/blog/glm-5.3>)

## Sources and related links

Prices, limits, capabilities, endpoints, and availability come from the public Impossibl catalog. Creator documentation supplies descriptions and release dates where available; it does not override the published API offering.

- [Public Impossibl model catalog](<https://api.impossibl.com/v1/models>)
- [Full model directory as JSON](<https://impossibl.com/models.json>)
- [GLM-5.3 Fast: model details and pricing](<https://impossibl.com/zai/glm-5.3-fast>)
- [Model directory](<https://impossibl.com/models>)
- [Fireworks serverless pricing](<https://docs.fireworks.ai/serverless/pricing>)
- [Z.AI release announcement](<https://z.ai/blog/glm-5.3>)