# GLM-5.1

GLM-5.1 is a text generation model from Z.AI, available through the Impossibl API. Its published context window is 200,000 tokens. The advertised input rate is $1.40 per million input tokens. The advertised output rate is $4.40 per million output tokens.

- Model identifier: ` zai/glm-5.1 `
- Creator: Z.AI
- Model type: Text generation
- Canonical model page: [GLM-5.1](<https://impossibl.com/zai/glm-5.1>)
- API availability: Listed as serving through Impossibl.
- Creator release date: 2026-04-07

## Capabilities and limits

- Context window: 200,000 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-5.1 ` 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 An unpublished rate is unknown, not zero.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 | $1.40 | per million input tokens |
| Output | $4.40 | per million output tokens |
| Cache read | $0.26 | 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 |

## Independent benchmarks

Source: [Artificial Analysis](<https://artificialanalysis.ai/>). Last checked: 2026-09-11T11:52:20.926Z.
Configurations are evaluated separately. API scores retain their original units. Unmeasured scores are omitted.

### GLM-5.1 (Reasoning)

Source: [Evaluation source](<https://artificialanalysis.ai/models/glm-5-1>)

| Benchmark | Score |
| --- | --- |
| Intelligence Index | 26.45 |
| Omniscience Index | 0.85 |
| GPQA | 86.77% |
| Humanity’s Last Exam | 30.07% |
| SciCode | 44.79% |
| CritPt | 4.57% |
| Terminal-Bench v2.1 | 61.80% |
| Terminal-Bench v4.0 | 2.02% |
| Terminal-Bench Hard | 43.18% |
| AA-LCR | 73.67% |
| GDPval Elo | 1180.01 |
| GDP.pdf All-pass | 8.40% |
| AutomationBench Partial | 20.31% |
| IFBench | 76.26% |
| Tau2 | 97.66% |
| Tau Banking | 13.61% |
| ITBench | 40.25% |
| coding index (API) | 55.8 |
| agentic index (API) | 25.2 |
| intelligence index (API) | 26.4 |

### GLM-5.1 (Non-reasoning)

Source: [Evaluation source](<https://artificialanalysis.ai/models/glm-5-1-non-reasoning>)

| Benchmark | Score |
| --- | --- |
| Intelligence Index | 24.24 |
| Omniscience Index | -22.43 |
| GPQA | 83.94% |
| Humanity’s Last Exam | 27.94% |
| CritPt | 0.00% |
| Terminal-Bench Hard | 35.61% |
| AA-LCR | 53.33% |
| IFBench | 51.97% |
| Tau2 | 97.08% |
| intelligence index (API) | 24.2 |

Full benchmark data and breakdowns: [Complete benchmark snapshot](<https://api.impossibl.com/v1/models/zai/glm-5.1/benchmarks>).


## Availability and retirement

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

## Frequently asked questions

### What is GLM-5.1?

GLM-5.1 is a text-generation model from Z.AI, available through the Impossibl API.

### How much does GLM-5.1 cost?

GLM-5.1 costs $1.40 per million input tokens and $4.40 per million output tokens through the Impossibl API. Cache reads cost $0.26 per million tokens. All rates are in USD.

### What is the context length of GLM-5.1?

GLM-5.1 has a 200,000-token context window through the Impossibl API.

### What inputs and outputs does GLM-5.1 support?

GLM-5.1 accepts text as input. GLM-5.1 returns text.

### How do I use GLM-5.1 through an API?

GLM-5.1 is available through the Impossibl API. Use zai/glm-5.1 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-5.1 released?

Z.AI released GLM-5.1 on April 7, 2026.

Sources: [Creator release announcement](<https://docs.z.ai/release-notes/new-released>)

## 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-5.1: model details and pricing](<https://impossibl.com/zai/glm-5.1>)
- [Model directory](<https://impossibl.com/models>)