overview changedmodels/sonnet-4-5/overview
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11---
22title: Claude Sonnet 4.5
33url: https://platform.claude.com/docs/en/models/sonnet-4-5/overview
4description: "Claude Sonnet 4.5 reference: lifecycle status, model IDs on every platform, context window, output limits, pricing, and migration resources. Claude Sonnet 4.5 is a legacy model; Claude Sonnet 5 is the current Sonnet model."
4description: "Claude Sonnet 4.5 reference: lifecycle status, model IDs on every platform, context window, output limits, pricing, and migration resources. Claude Sonnet 4.5 is a legacy model; Claude Sonnet 5.5 is the current Sonnet model."
55---
66
77**Legacy.** Released September 29, 2025.
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9Although Claude Sonnet 4.5 is still available, you should consider migrating to Claude Sonnet 5 for improved performance. [See Claude Sonnet 5](https://platform.claude.com/docs/en/models/sonnet-5/overview) · [Migrate to Claude Sonnet 5](https://platform.claude.com/docs/en/models/sonnet-5/migration-guide#migrating-from-sonnet-45)
9Although Claude Sonnet 4.5 is still available, you should consider migrating to Claude Sonnet 5.5 for improved performance. [See Claude Sonnet 5.5](https://platform.claude.com/docs/en/models/sonnet-5-5/overview) · [Migrate to Claude Sonnet 5.5](https://platform.claude.com/docs/en/models/sonnet-5-5/migration-guide)
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1111Model ID: `claude-sonnet-4-5-20250929`
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1616
1717## How it compares to the current lineup
1818
19| Model | Context | Max output | Price / MTok | Thinking | Default effort | Knowledge cutoff |
20| :-------------------------------------------------------------------------------- | :------ | :--------- | :----------- | :------------------- | :------------- | :--------------- |
21| [Claude Fable 5.1](https://platform.claude.com/docs/en/models/fable-5-1/overview) | 1M | 128K | $10 / $50 | Adaptive (always on) | `high` | Jun 2026 |
22| [Claude Opus 5.5](https://platform.claude.com/docs/en/models/opus-5-5/overview) | 1M | 128K | $4 / $20 | Adaptive (always on) | `medium` | Jun 2026 |
23| [Claude Sonnet 5](https://platform.claude.com/docs/en/models/sonnet-5/overview) | 1M | 128K | $2 / $10 | Adaptive | `high` | Jan 2026 |
24| **Claude Sonnet 4.5** (this model) | 200K | 64K | $3 / $15 | Extended | — | Jan 2025 |
25| [Claude Haiku 4.5](https://platform.claude.com/docs/en/models/haiku-4-5/overview) | 200K | 64K | $1 / $5 | Extended | — | Feb 2025 |
19| Model | Context | Max output | Price / MTok | Thinking | Default effort | Knowledge cutoff |
20| :---------------------------------------------------------------------------------- | :------ | :--------- | :----------- | :------------------- | :------------- | :--------------- |
21| [Claude Fable 5.1](https://platform.claude.com/docs/en/models/fable-5-1/overview) | 1M | 128K | $10 / $50 | Adaptive (always on) | `high` | Jun 2026 |
22| [Claude Opus 5.5](https://platform.claude.com/docs/en/models/opus-5-5/overview) | 1M | 128K | $4 / $20 | Adaptive (always on) | `medium` | Jun 2026 |
23| [Claude Sonnet 5.5](https://platform.claude.com/docs/en/models/sonnet-5-5/overview) | 1M | 128K | $2 / $10 | Adaptive | `high` | Jun 2026 |
24| **Claude Sonnet 4.5** (this model) | 200K | 64K | $3 / $15 | Extended | — | Jan 2025 |
25| [Claude Haiku 4.5](https://platform.claude.com/docs/en/models/haiku-4-5/overview) | 200K | 64K | $1 / $5 | Extended | — | Feb 2025 |
2626
2727* **Context:** 1M tokens is roughly 555k words or 2.5M Unicode characters on the current tokenizer (introduced with Claude Opus 4.7); models before it fit about 750k words in 1M tokens. 200k tokens is roughly 150k words.
28* **Max output:** Synchronous Messages API limit. On the Message Batches API, Claude Opus 5.5, Claude Opus 5, Claude Sonnet 5, Claude Opus 4.8, Claude Opus 4.7, Claude Opus 4.6, and Claude Sonnet 4.6 support up to 300k output tokens with the output-300k-2026-03-24 beta header.
28* **Max output:** Synchronous Messages API limit. On the Message Batches API, Claude Opus 5.5, Claude Opus 5, Claude Sonnet 5.5, Claude Sonnet 5, Claude Opus 4.8, Claude Opus 4.7, Claude Opus 4.6, and Claude Sonnet 4.6 support up to 300k output tokens with the output-300k-2026-03-24 beta header.
2929* **Price / MTok:** Input / output, base price per million tokens. Batch API requests are 50% off; prompt caching reads cost 10% of the base input price (2.5% on Claude Fable 5.1 and Claude Mythos 5.1, 5% on Claude Opus 5.5). See Pricing for the full list.
3030* **Thinking:** Adaptive thinking lets the model decide how much to think, steered by effort. Extended thinking is the manual budget\_tokens mode on earlier models.
3131* **Default effort:** The effort parameter’s default on the Claude API. Models without a value don’t support the parameter.
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8181## Resources
8282
8383<CardGroup cols={3}>
84 <Card title="Migrate to Claude Sonnet 5" icon="arrows-left-right" href="https://platform.claude.com/docs/en/models/sonnet-5/migration-guide#migrating-from-sonnet-45">
85 What changes when moving from Claude Sonnet 4.5 and earlier Sonnet models to Claude Sonnet 5.
84 <Card title="Migrate to Claude Sonnet 5.5" icon="arrows-left-right" href="https://platform.claude.com/docs/en/models/sonnet-5-5/migration-guide#migrating-from-claude-sonnet-4-6">
85 What changes when moving from Claude Sonnet 4.5 and earlier Sonnet models to Claude Sonnet 5.5.
8686 </Card>
8787
88 <Card title="Claude Sonnet 5" icon="arrow-right" href="https://platform.claude.com/docs/en/models/sonnet-5/overview">
88 <Card title="Claude Sonnet 5.5" icon="arrow-right" href="https://platform.claude.com/docs/en/models/sonnet-5-5/overview">
8989 The current Sonnet model: overview, specs, and resources.
9090 </Card>
9191</CardGroup>
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