# Claude Sonnet 4.5

Claude Sonnet 4.5 is a text generation model from Anthropic, available through the Impossibl API. Its published context window is 200,000 tokens. The advertised input rate is $3.00 per million input tokens. The advertised output rate is $15.00 per million output tokens.

- Model identifier: ` anthropic/claude-sonnet-4-5 `
- Creator: Anthropic
- Model type: Text generation
- Canonical model page: [Claude Sonnet 4.5](<https://impossibl.com/anthropic/claude-sonnet-4-5>)
- API availability: Listed as serving through Impossibl.
- Creator release date: 2025-09-29

## 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, image
- Outputs: text
- Tool calling: Not published

## API access

Use ` anthropic/claude-sonnet-4-5 ` 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 An unpublished rate is unknown, not zero.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 | $3.00 | per million input tokens |
| Output | $15.00 | per million output tokens |
| Cache read | $0.30 | per million cached input tokens |
| Cache write (default retention) | $3.75 | per million tokens |
| Cache write (one-hour retention) | $6.00 | per million tokens |
| Audio input | Not published | per million audio input tokens |

## Independent benchmarks

Source: [Artificial Analysis](<https://artificialanalysis.ai/>). Last checked: 2026-09-11T11:21:18.106Z.
Configurations are evaluated separately. API scores retain their original units. Unmeasured scores are omitted.

### Claude 4.5 Sonnet (Non-reasoning)

Source: [Evaluation source](<https://artificialanalysis.ai/models/claude-4-5-sonnet>)

| Benchmark | Score |
| --- | --- |
| Intelligence Index | 19.34 |
| Omniscience Index | -9.37 |
| GPQA | 72.73% |
| Humanity’s Last Exam | 7.23% |
| CritPt | 0.00% |
| Terminal-Bench Hard | 28.79% |
| AA-LCR | 54.00% |
| MMMU-Pro | 65.20% |
| IFBench | 42.65% |
| Tau2 | 70.47% |
| LiveCodeBench | 59.05% |
| AIME 2025 | 37.00% |
| intelligence index (API) | 19.3 |

### Claude 4.5 Sonnet (Reasoning)

Source: [Evaluation source](<https://artificialanalysis.ai/models/claude-4-5-sonnet-thinking>)

| Benchmark | Score |
| --- | --- |
| Intelligence Index | 21.18 |
| Omniscience Index | -0.08 |
| GPQA | 83.43% |
| Humanity’s Last Exam | 17.79% |
| SciCode | 45.72% |
| CritPt | 1.14% |
| Terminal-Bench v2.1 | 55.81% |
| Terminal-Bench v4.0 | 0.00% |
| Terminal-Bench Hard | 35.61% |
| AA-LCR | 72.33% |
| GDPval Elo | 989.26 |
| GDP.pdf All-pass | 5.20% |
| AutomationBench Partial | 14.08% |
| MMMU-Pro | 68.73% |
| IFBench | 57.28% |
| Tau2 | 78.07% |
| Tau Banking | 24.54% |
| LiveCodeBench | 71.43% |
| AIME 2025 | 88.00% |
| coding index (API) | 52.1 |
| agentic index (API) | 17.5 |
| intelligence index (API) | 21.2 |

Full benchmark data and breakdowns: [Complete benchmark snapshot](<https://api.impossibl.com/v1/models/anthropic/claude-sonnet-4-5/benchmarks>).


## Availability and retirement

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

## Frequently asked questions

### What is Claude Sonnet 4.5?

Claude Sonnet 4.5 is a text-generation model from Anthropic, available through the Impossibl API.

### How much does Claude Sonnet 4.5 cost?

Claude Sonnet 4.5 costs $3.00 per million input tokens and $15.00 per million output tokens through the Impossibl API. Cache reads cost $0.30 per million tokens; cache writes cost $3.75 per million tokens; cache writes with one-hour retention cost $6.00 per million tokens. All rates are in USD.

### What is the context length of Claude Sonnet 4.5?

Claude Sonnet 4.5 has a 200,000-token context window through the Impossibl API.

### What inputs and outputs does Claude Sonnet 4.5 support?

Claude Sonnet 4.5 accepts text and image as input. Claude Sonnet 4.5 returns text.

### How do I use Claude Sonnet 4.5 through an API?

Claude Sonnet 4.5 is available through the Impossibl API. Use anthropic/claude-sonnet-4-5 as the model identifier with /v1/chat/completions. The quickstart explains how to create an API key and send your first request.

### When was Claude Sonnet 4.5 released?

Anthropic released Claude Sonnet 4.5 on September 29, 2025.

Sources: [Creator release announcement](<https://www.anthropic.com/news/claude-sonnet-4-5>)

## 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>)
- [Claude Sonnet 4.5: model details and pricing](<https://impossibl.com/anthropic/claude-sonnet-4-5>)
- [Model directory](<https://impossibl.com/models>)