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266266Set these environment variables to specific Amazon Bedrock model IDs.
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268Without `ANTHROPIC_DEFAULT_OPUS_MODEL`, the `opus` alias on Amazon Bedrock resolves to Opus 5, and without `ANTHROPIC_DEFAULT_SONNET_MODEL`, the `sonnet` alias resolves to Sonnet 4.5. This example pins each alias to a specific version:
268Without `ANTHROPIC_DEFAULT_OPUS_MODEL`, the `opus` alias on Amazon Bedrock resolves to Opus 5.5, and without `ANTHROPIC_DEFAULT_SONNET_MODEL`, the `sonnet` alias resolves to Sonnet 4.5. This example pins each alias to a specific version:
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270270```bash theme={null}
271271export ANTHROPIC_DEFAULT_OPUS_MODEL='us.anthropic.claude-opus-4-8'
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278278To keep the built-in default models and change only their preferred prefix, set [`ANTHROPIC_BEDROCK_REGION_PREFIX`](#cross-region-inference-profile-prefixes) instead of pinning. The difference shows in what the `opus` alias resolves to:
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280| You set | The `opus` alias resolves to |
281| :------------------------------------------------------------ | :---------------------------------------------------------------------------- |
282| `ANTHROPIC_DEFAULT_OPUS_MODEL='us.anthropic.claude-opus-4-8'` | `us.anthropic.claude-opus-4-8`, the exact ID you pinned |
283| `ANTHROPIC_BEDROCK_REGION_PREFIX=eu` | `eu.anthropic.claude-opus-5`, the built-in default with your preferred prefix |
280| You set | The `opus` alias resolves to |
281| :------------------------------------------------------------ | :------------------------------------------------------------------------------ |
282| `ANTHROPIC_DEFAULT_OPUS_MODEL='us.anthropic.claude-opus-4-8'` | `us.anthropic.claude-opus-4-8`, the exact ID you pinned |
283| `ANTHROPIC_BEDROCK_REGION_PREFIX=eu` | `eu.anthropic.claude-opus-5-5`, the built-in default with your preferred prefix |
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285285For current and legacy model IDs, see [Models overview](https://platform.claude.com/docs/en/about-claude/models/overview). For the full list of pinning environment variables, see [Model configuration](/docs/en/model-config#pin-models-for-third-party-deployments).
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288288
289289| Model type | Default model |
290290| :--------------- | :---------------------------------------------------------------------------------------- |
291| Primary model | Opus 5, for example `us.anthropic.claude-opus-5` in a `us-*` region |
291| Primary model | Opus 5.5, for example `us.anthropic.claude-opus-5-5` in a `us-*` region |
292292| Small/fast model | Sonnet 4.5, for example `us.anthropic.claude-sonnet-4-5-20250929-v1:0` in a `us-*` region |
293293
294294Background tasks such as session title generation use the small/fast model, normally a Haiku-class model. On Amazon Bedrock, Claude Code uses the default Sonnet model for background tasks because Haiku may not be enabled in every account or region. Two selections change which model carries them:
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300300 Opus models have a higher per-token price than Sonnet models, so a deployment that doesn't pin a primary model is billed at the Opus rate once it updates to v2.1.207 or later. To keep Sonnet 4.5 as the primary model, set `ANTHROPIC_MODEL` to its full model ID. A deployment that steers the default with `ANTHROPIC_DEFAULT_SONNET_MODEL` and doesn't set `ANTHROPIC_DEFAULT_OPUS_MODEL` keeps its steered Sonnet model as the default.
301301</Warning>
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303On v2.1.207 through v2.1.218, the primary model on Amazon Bedrock defaulted to Opus 4.8 and the `opus` alias resolved to Opus 4.8. Before v2.1.207, the primary model defaulted to Sonnet 4.5, the `opus` alias resolved to Opus 4.6, and background tasks always used the primary model.
303Before v2.1.280, the primary model on Amazon Bedrock defaulted to Opus 5 and the `opus` alias resolved to Opus 5 from v2.1.219. On v2.1.207 through v2.1.218, the primary model on Amazon Bedrock defaulted to Opus 4.8 and the `opus` alias resolved to Opus 4.8. Before v2.1.207, the primary model defaulted to Sonnet 4.5, the `opus` alias resolved to Opus 4.6, and background tasks always used the primary model.
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305305To customize models further, use one of these methods:
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373373```bash theme={null}
374374export ANTHROPIC_BEDROCK_REGION_PREFIX=global
375375# In a us-* region, the primary model now resolves to
376# global.anthropic.claude-opus-5 instead of us.anthropic.claude-opus-5
376# global.anthropic.claude-opus-5-5 instead of us.anthropic.claude-opus-5-5
377377```
378378
379379The preferred prefix is a preference, not a guarantee, whether it comes from your region or from the variable. How Claude Code applies it depends on whether it can check profile availability in your account: