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Or, for the model with the same capabilities and no access approval requirement:
about-claude/models/migration-guide
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## Migrating to Claude Mythos 5 and Claude Fable 5 -[Claude Fable 5](https://platform.claude.com/docs/en/about-claude/models/introducing-claude-fable-5-and-claude-mythos-5) is Anthropic's most capable widely released model, available on the Claude API, [Amazon Bedrock](https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock), [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), [Google Cloud](https://platform.claude.com/docs/en/build-with-claude/claude-on-vertex-ai), and [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry). [Claude Mythos 5](https://anthropic.com/glasswing) shares the same capabilities and is offered only to approved customers in Project Glasswing. +[Claude Fable 5](https://platform.claude.com/docs/en/models/fable-5/introducing-claude-fable-5-and-claude-mythos-5) is Anthropic's most capable widely released model, available on the Claude API, [Amazon Bedrock](https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock), [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), [Google Cloud](https://platform.claude.com/docs/en/build-with-claude/claude-on-vertex-ai), and [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry). [Claude Mythos 5](https://anthropic.com/glasswing) shares the same capabilities and is offered only to approved customers in Project Glasswing. The baseline settings shared by `claude-fable-5` and `claude-mythos-5`:
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### Migrating to Claude Mythos 5 and Claude Fable 5 from Claude Mythos Preview -[Claude Mythos 5](https://anthropic.com/glasswing) is the access-gated successor to [Claude Mythos Preview](https://anthropic.com/glasswing), the invitation-only research preview. [Claude Fable 5](https://platform.claude.com/docs/en/about-claude/models/introducing-claude-fable-5-and-claude-mythos-5) offers the same capabilities and does not require access approval. The changes in this section apply equally to both targets. +[Claude Mythos 5](https://anthropic.com/glasswing) is the access-gated successor to [Claude Mythos Preview](https://anthropic.com/glasswing), the invitation-only research preview. [Claude Fable 5](https://platform.claude.com/docs/en/models/fable-5/introducing-claude-fable-5-and-claude-mythos-5) offers the same capabilities and does not require access approval. The changes in this section apply equally to both targets. Migration is mostly drop-in. Claude Mythos 5 and Claude Fable 5 use the same [Messages API](https://platform.claude.com/docs/en/build-with-claude/working-with-messages) and the same [tool use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview) patterns as Claude Mythos Preview, and token counts are roughly unchanged because all three models use the same tokenizer. The key changes to check are the features that are no longer available (listed in the next section) and thinking output. If you migrate to Claude Fable 5, also plan for safety classifier refusals, which Claude Mythos Preview and Claude Mythos 5 do not have; see [Refusals and fallback](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback).
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### Migrating to Claude Mythos 5 and Claude Fable 5 from Claude Opus 5 -Claude Fable 5 and Claude Mythos 5 use the same [Messages API](https://platform.claude.com/docs/en/build-with-claude/working-with-messages) and the same [tool use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview) patterns as Claude Opus 5, with the same [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) by default and the same [128k max output tokens](https://platform.claude.com/docs/en/about-claude/models/overview). The prefill and sampling-parameter restrictions, and the thinking display behavior, carry over from Claude Opus 5 unchanged. The changes to check are always-on thinking, pricing, Priority Tier, and data retention. +Claude Fable 5 and Claude Mythos 5 use the same [Messages API](https://platform.claude.com/docs/en/build-with-claude/working-with-messages) and the same [tool use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview) patterns as Claude Opus 5, with the same [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) by default and the same [128k max output tokens](https://platform.claude.com/docs/en/models/overview). The prefill and sampling-parameter restrictions, and the thinking display behavior, carry over from Claude Opus 5 unchanged. The changes to check are always-on thinking, pricing, Priority Tier, and data retention. #### Update your model name
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If your code is on Claude Opus 4.7 or earlier, first apply the relevant [Migrating to Claude Opus 5](https://platform.claude.com/docs/en/about-claude/models/migration-guide#migrating-to-claude-opus-5) from-section for the API-level changes from your current model, then the remaining delta in this section. </Note> -Migration is mostly drop-in. Claude Fable 5 and Claude Mythos 5 use the same [Messages API](https://platform.claude.com/docs/en/build-with-claude/working-with-messages) and the same [tool use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview) patterns as Claude Opus 4.8, with the same [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) by default and the same [128k max output tokens](https://platform.claude.com/docs/en/about-claude/models/overview). Token counts are roughly unchanged because the models use the same tokenizer. The key changes to check are always-on [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), thinking output, safety classifier refusals (Claude Fable 5 only), and pricing. +Migration is mostly drop-in. Claude Fable 5 and Claude Mythos 5 use the same [Messages API](https://platform.claude.com/docs/en/build-with-claude/working-with-messages) and the same [tool use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview) patterns as Claude Opus 4.8, with the same [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) by default and the same [128k max output tokens](https://platform.claude.com/docs/en/models/overview). Token counts are roughly unchanged because the models use the same tokenizer. The key changes to check are always-on [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), thinking output, safety classifier refusals (Claude Fable 5 only), and pricing. #### Update your model name
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Claude Opus 5 is a step-change improvement over Claude Opus 4.8, strong on deep reasoning, agentic and long-horizon tasks, and test-time compute scaling. For behavioral differences and model-specific prompting patterns, see [Prompting Claude Opus 5](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-opus-5). -Claude Opus 5 is a drop-in upgrade for Claude Opus 4.8 at the same pricing of $5 per million input tokens and $25 per million output tokens; see [Claude pricing](https://platform.claude.com/docs/en/about-claude/pricing). There are two breaking changes for code already running on Claude Opus 4.8, covered under Breaking changes below. Claude Opus 5 supports the same set of features as Claude Opus 4.8, including the [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) (the default, with no beta header), [128k max output tokens](https://platform.claude.com/docs/en/about-claude/models/overview), [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching), [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview), with two exceptions: [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) is not available on Claude Opus 5, and [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not supported on Claude Opus 5. See each tool page for model availability. +Claude Opus 5 is a drop-in upgrade for Claude Opus 4.8 at the same pricing of $5 per million input tokens and $25 per million output tokens; see [Claude pricing](https://platform.claude.com/docs/en/about-claude/pricing). There are two breaking changes for code already running on Claude Opus 4.8, covered under Breaking changes below. Claude Opus 5 supports the same set of features as Claude Opus 4.8, including the [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) (the default, with no beta header), [128k max output tokens](https://platform.claude.com/docs/en/models/overview), [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching), [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview), with two exceptions: [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) is not available on Claude Opus 5, and [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not supported on Claude Opus 5. See each tool page for model availability. ### Migrating to Claude Opus 5 from Claude Opus 4.8
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### Migrating to Claude Opus 5 from Claude Opus 4.7 -Claude Opus 5 should have strong out-of-the-box performance on existing Claude Opus 4.7 prompts and evals, at the same pricing of $5 per million input tokens and $25 per million output tokens. It supports the same set of features as Claude Opus 4.7, including the [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows), [128k max output tokens](https://platform.claude.com/docs/en/about-claude/models/overview), [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching), [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview), with two exceptions: [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) is not available on Claude Opus 5, and [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not supported on Claude Opus 5. It also adds [mid-conversation system messages](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages) and publicly documents [refusal stop details](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback#refusal-response). On the Claude API, Claude Opus 5 also supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the stable `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages, neither of which Claude Opus 4.7 supports; existing integrations on the earlier `computer_20251124` version continue to work unchanged on both models. To upgrade an existing integration, see [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). +Claude Opus 5 should have strong out-of-the-box performance on existing Claude Opus 4.7 prompts and evals, at the same pricing of $5 per million input tokens and $25 per million output tokens. It supports the same set of features as Claude Opus 4.7, including the [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows), [128k max output tokens](https://platform.claude.com/docs/en/models/overview), [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching), [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview), with two exceptions: [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) is not available on Claude Opus 5, and [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not supported on Claude Opus 5. It also adds [mid-conversation system messages](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages) and publicly documents [refusal stop details](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback#refusal-response). On the Claude API, Claude Opus 5 also supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the stable `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages, neither of which Claude Opus 4.7 supports; existing integrations on the earlier `computer_20251124` version continue to work unchanged on both models. To upgrade an existing integration, see [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). <Note> If your code is on Claude Opus 4.6 or earlier, use [Migrating to Claude Opus 5 from Claude Opus 4.6 and earlier Opus models](https://platform.claude.com/docs/en/about-claude/models/migration-guide#migrating-from-claude-opus-46) instead. That section includes breaking changes (sampling parameters rejected, manual extended thinking rejected, new tokenizer) that the upgrade from Claude Opus 4.7 alone does not cover.
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Claude Opus 5 should have strong out-of-the-box performance on existing Claude Opus 4.6 prompts and evals at the same pricing, but there are a handful of behavioral and API changes worth knowing about as you migrate. Most of these changes took effect in Claude Opus 4.7; two more, thinking on by default and an effort cap on disabling thinking, take effect on Claude Opus 5. All of them are covered below, so this section is complete for code coming straight from Claude Opus 4.6. Claude Opus 5 supports the same set of features as Claude Opus 4.6, including: * [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) at standard API pricing with no long-context premium -* [128k max output tokens](https://platform.claude.com/docs/en/about-claude/models/overview) +* [128k max output tokens](https://platform.claude.com/docs/en/models/overview) * [Adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) * [Prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching) * [Batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing)
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### Migrating to Claude Opus 5 from Claude Sonnet 5 -Claude Opus 5 and Claude Sonnet 5 share the same API surface: both run with [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) on by default, both default the [effort parameter](https://platform.claude.com/docs/en/build-with-claude/effort) to `high` on the Claude API and Claude Code, both serve a [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) by default with [128k max output tokens](https://platform.claude.com/docs/en/about-claude/models/overview), and neither supports [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models). Manual extended thinking and non-default sampling parameters return a 400 error on both models, as does assistant prefill. +Claude Opus 5 and Claude Sonnet 5 share the same API surface: both run with [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) on by default, both default the [effort parameter](https://platform.claude.com/docs/en/build-with-claude/effort) to `high` on the Claude API and Claude Code, both serve a [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) by default with [128k max output tokens](https://platform.claude.com/docs/en/models/overview), and neither supports [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models). Manual extended thinking and non-default sampling parameters return a 400 error on both models, as does assistant prefill. #### Update your model name
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2. **Disabling thinking is capped at `high` effort:** On Claude Sonnet 5, `thinking: {type: "disabled"}` is accepted at any effort level. On Claude Opus 5, it is accepted only at an [effort](https://platform.claude.com/docs/en/build-with-claude/effort) level of `high` or below; a request that combines `thinking: {type: "disabled"}` with effort `xhigh` or `max` returns a 400 error, enforced on each request. Audit requests that disable thinking before you migrate. -3. **Mid-conversation system messages:** Claude Opus 5 accepts `role: "system"` messages immediately after a user turn in the `messages` array (subject to [placement rules](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages#limitations)). This feature is not available on Claude Sonnet 5; use the top-level `system` field instead. If you maintain code paths that rebuild the full message history to update instructions, you can simplify them and preserve [prompt cache](https://platform.claude.com/docs/en/build-with-claude/prompt-caching) hits on earlier turns. +3. **Mid-conversation system messages:** Claude Opus 5 accepts `role: "system"` messages immediately after a user turn in the `messages` array (subject to [placement rules](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages#limitations)). This feature is not available on Claude Sonnet 5. If you maintain code paths that rebuild the full message history to update instructions, you can simplify them and preserve [prompt cache](https://platform.claude.com/docs/en/build-with-claude/prompt-caching) hits on earlier turns. 4. **Web fetch is not available:** The [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) tool is available on Claude Sonnet 5 but not on Claude Opus 5.
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### Migrating to Claude Sonnet 5 from Claude Haiku 4.5 -Claude Haiku 4.5 and Claude Sonnet 5 differ more at the API level than adjacent models within one class: Claude Haiku 4.5 uses manual [extended thinking](https://platform.claude.com/docs/en/build-with-claude/extended-thinking) (off by default), a 200k token context window, and up to 64k output tokens, while Claude Sonnet 5 runs with [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) on by default, serves a [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) by default, and supports up to [128k output tokens](https://platform.claude.com/docs/en/about-claude/models/overview). +Claude Haiku 4.5 and Claude Sonnet 5 differ more at the API level than adjacent models within one class: Claude Haiku 4.5 uses manual [extended thinking](https://platform.claude.com/docs/en/build-with-claude/extended-thinking) (off by default), a 200k token context window, and up to 64k output tokens, while Claude Sonnet 5 runs with [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) on by default, serves a [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) by default, and supports up to [128k output tokens](https://platform.claude.com/docs/en/models/overview). #### Update your model name
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Claude Haiku 4.5 is the fastest and most intelligent Haiku model with near-frontier performance, delivering premium model quality for interactive applications and high-volume processing. -For a complete overview of capabilities, see the [models overview](https://platform.claude.com/docs/en/about-claude/models/overview). +For a complete overview of capabilities, see the [models overview](https://platform.claude.com/docs/en/models/overview). <Note> For Claude Haiku 4.5 pricing, see [Claude pricing](https://platform.claude.com/docs/en/about-claude/pricing).
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**Review new rate limits:** Haiku 4.5 has separate rate limits from Haiku 3.5. See [Rate limits](https://platform.claude.com/docs/en/api/rate-limits) documentation for details. -**Explore new capabilities:** See the [models overview](https://platform.claude.com/docs/en/about-claude/models/overview) for details on context awareness, increased output capacity (64k tokens), higher intelligence, and improved speed. +**Explore new capabilities:** See the [models overview](https://platform.claude.com/docs/en/models/overview) for details on context awareness, increased output capacity (64k tokens), higher intelligence, and improved speed. #### Breaking changes
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## Get help * Check the [API documentation](https://platform.claude.com/docs/en/api/overview) for detailed specifications -* Review [model capabilities](https://platform.claude.com/docs/en/about-claude/models/overview) for performance comparisons +* Review [model capabilities](https://platform.claude.com/docs/en/models/overview) for performance comparisons * Review [API release notes](https://platform.claude.com/docs/en/release-notes/api) for API updates * Contact support if you encounter any issues during migration
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## Migrating to Claude Mythos 5 and Claude Fable 5 -[Claude Fable 5](https://platform.claude.com/docs/en/about-claude/models/introducing-claude-fable-5-and-claude-mythos-5) is Anthropic's most capable widely released model, generally available on the Claude API, [Amazon Bedrock](https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock), [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), [Google Cloud](https://platform.claude.com/docs/en/build-with-claude/claude-on-vertex-ai), and [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry). [Claude Mythos 5](https://anthropic.com/glasswing) shares the same capabilities and is offered in limited availability to approved customers in Project Glasswing. +[Claude Fable 5](https://platform.claude.com/docs/en/about-claude/models/introducing-claude-fable-5-and-claude-mythos-5) is Anthropic's most capable widely released model, available on the Claude API, [Amazon Bedrock](https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock), [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), [Google Cloud](https://platform.claude.com/docs/en/build-with-claude/claude-on-vertex-ai), and [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry). [Claude Mythos 5](https://anthropic.com/glasswing) shares the same capabilities and is offered only to approved customers in Project Glasswing. The baseline settings shared by `claude-fable-5` and `claude-mythos-5`:
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Where the two models diverge: -* **Availability:** Claude Fable 5 is generally available. Claude Mythos 5 is available only to approved customers in [Project Glasswing](https://anthropic.com/glasswing). +* **Availability:** Claude Fable 5 does not require access approval. Claude Mythos 5 is available only to approved customers in [Project Glasswing](https://anthropic.com/glasswing). * **Safety classifiers:** Claude Fable 5 runs safety classifiers that can decline requests with `stop_reason: "refusal"`. Claude Mythos 5 does not include these classifiers. See [Refusals and fallback](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback). * **Priority Tier:** [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is supported on Claude Fable 5 but not on Claude Mythos 5. ### Migrating to Claude Mythos 5 and Claude Fable 5 from Claude Mythos Preview -[Claude Mythos 5](https://anthropic.com/glasswing) is the access-gated successor to [Claude Mythos Preview](https://anthropic.com/glasswing), the invitation-only research preview. [Claude Fable 5](https://platform.claude.com/docs/en/about-claude/models/introducing-claude-fable-5-and-claude-mythos-5) is the generally available model with the same capabilities, and the changes in this section apply equally to both targets. +[Claude Mythos 5](https://anthropic.com/glasswing) is the access-gated successor to [Claude Mythos Preview](https://anthropic.com/glasswing), the invitation-only research preview. [Claude Fable 5](https://platform.claude.com/docs/en/about-claude/models/introducing-claude-fable-5-and-claude-mythos-5) offers the same capabilities and does not require access approval. The changes in this section apply equally to both targets. Migration is mostly drop-in. Claude Mythos 5 and Claude Fable 5 use the same [Messages API](https://platform.claude.com/docs/en/build-with-claude/working-with-messages) and the same [tool use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview) patterns as Claude Mythos Preview, and token counts are roughly unchanged because all three models use the same tokenizer. The key changes to check are the features that are no longer available (listed in the next section) and thinking output. If you migrate to Claude Fable 5, also plan for safety classifier refusals, which Claude Mythos Preview and Claude Mythos 5 do not have; see [Refusals and fallback](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback).
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model = "claude-mythos-preview" # Before model = "claude-mythos-5" # After -# Or, for the generally available model with the same capabilities: +# Or, for the model with the same capabilities and no access approval requirement: model = "claude-fable-5" # After ```
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#### Migration checklist -* Update the model name from `claude-mythos-preview` to `claude-mythos-5`, or to `claude-fable-5` for the generally available model. +* Update the model name from `claude-mythos-preview` to `claude-mythos-5`, or to `claude-fable-5`, which offers the same capabilities and does not require access approval. * Remove manual extended thinking configuration (`thinking: {type: "enabled", budget_tokens: N}`). Adaptive thinking is always on, and no `thinking` field is required. * Remove any `thinking: {type: "disabled"}` configuration. Disabling thinking returns an error on `claude-mythos-5` and `claude-fable-5`. * Remove `budget_tokens`. It has no direct replacement: thinking is adaptive, and the `effort` parameter is a separate output-level control, not a thinking budget.
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### Migrating to Claude Opus 5 from Claude Opus 4.7 -Claude Opus 5 should have strong out-of-the-box performance on existing Claude Opus 4.7 prompts and evals, at the same pricing of $5 per million input tokens and $25 per million output tokens. It supports the same set of features as Claude Opus 4.7, including the [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows), [128k max output tokens](https://platform.claude.com/docs/en/about-claude/models/overview), [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching), [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview), with two exceptions: [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) is not available on Claude Opus 5, and [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not supported on Claude Opus 5. It also adds [mid-conversation system messages](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages) and publicly documents [refusal stop details](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback#refusal-response). On the Claude API, Claude Opus 5 also supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the generally available `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages, neither of which Claude Opus 4.7 supports; existing integrations on the earlier `computer_20251124` version continue to work unchanged on both models. To upgrade an existing integration, see [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). +Claude Opus 5 should have strong out-of-the-box performance on existing Claude Opus 4.7 prompts and evals, at the same pricing of $5 per million input tokens and $25 per million output tokens. It supports the same set of features as Claude Opus 4.7, including the [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows), [128k max output tokens](https://platform.claude.com/docs/en/about-claude/models/overview), [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching), [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview), with two exceptions: [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) is not available on Claude Opus 5, and [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not supported on Claude Opus 5. It also adds [mid-conversation system messages](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages) and publicly documents [refusal stop details](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback#refusal-response). On the Claude API, Claude Opus 5 also supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the stable `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages, neither of which Claude Opus 4.7 supports; existing integrations on the earlier `computer_20251124` version continue to work unchanged on both models. To upgrade an existing integration, see [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). <Note> If your code is on Claude Opus 4.6 or earlier, use [Migrating to Claude Opus 5 from Claude Opus 4.6 and earlier Opus models](https://platform.claude.com/docs/en/about-claude/models/migration-guide#migrating-from-claude-opus-46) instead. That section includes breaking changes (sampling parameters rejected, manual extended thinking rejected, new tokenizer) that the upgrade from Claude Opus 4.7 alone does not cover.
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The following items are not breaking changes; they describe behavior differences worth checking after you swap the model ID. -1. **Sampling parameters (unchanged):** Setting `temperature`, `top_p`, or `top_k` to a non-default value returns a 400 error on Claude Opus 5, the same as on Claude Opus 4.7. The SDK request types still define these fields for compatibility with earlier models, so code that sets them type-checks, but the API rejects the request server-side. If you removed these parameters when migrating to Opus 4.7, no further changes are needed. +1. **Sampling parameters (unchanged):** Setting `temperature`, `top_p`, or `top_k` to a non-default value returns a 400 error on Claude Opus 5, the same as on Claude Opus 4.7. Most SDKs still define these fields for compatibility with earlier models, so code that sets them type-checks even though the API rejects the request. The Python SDK (v1.0 and later) does not define them, and passing them raises a `TypeError`. If you removed these parameters when migrating to Opus 4.7, no further changes are needed. 2. **Effort default is `high`:** The [effort parameter](https://platform.claude.com/docs/en/build-with-claude/effort) default on Claude Opus 5 is `high` on the Claude API and Claude Code. If you already set effort explicitly, your setting is unchanged.
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* [Vision](https://platform.claude.com/docs/en/build-with-claude/vision) * Server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview) ([bash](https://platform.claude.com/docs/en/agents-and-tools/tool-use/bash-tool), [code execution](https://platform.claude.com/docs/en/agents-and-tools/tool-use/code-execution-tool), [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool), [text editor](https://platform.claude.com/docs/en/agents-and-tools/tool-use/text-editor-tool), [web search](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-search-tool), [MCP connector](https://platform.claude.com/docs/en/agents-and-tools/mcp-connector), [memory](https://platform.claude.com/docs/en/agents-and-tools/tool-use/memory-tool)) -Two exceptions: [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) is not available on Claude Opus 5, and [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not supported on Claude Opus 5. On the Claude API, Claude Opus 5 also supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the generally available `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages, neither of which Claude Opus 4.6 or earlier Opus models support; existing integrations on the earlier `computer_20251124` version continue to work unchanged on Claude Opus 5. To upgrade an existing integration, see [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). +Two exceptions: [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) is not available on Claude Opus 5, and [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not supported on Claude Opus 5. On the Claude API, Claude Opus 5 also supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the stable `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages, neither of which Claude Opus 4.6 or earlier Opus models support; existing integrations on the earlier `computer_20251124` version continue to work unchanged on Claude Opus 5. To upgrade an existing integration, see [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). #### Update your model name
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3. **Disabling thinking is capped at `high` effort:** You can turn thinking off with `thinking: {type: "disabled"}`, but only at an [effort](https://platform.claude.com/docs/en/build-with-claude/effort) level of `high` or below. A request that combines `thinking: {type: "disabled"}` with effort `xhigh` or `max` returns a 400 error on Claude Opus 5, enforced on each request. Audit requests that disable thinking before you migrate: re-enable thinking or lower the effort to `high` or below. -4. **Sampling parameters removed:** Setting `temperature`, `top_p`, or `top_k` to any non-default value on Claude Opus 4.7 or later models, including Claude Opus 5, returns a 400 error. The safest migration path is to omit these parameters entirely from request payloads. Prompting is the recommended way to guide model behavior on Claude Opus 5. If you were using `temperature = 0` for determinism, note that it never guaranteed identical outputs on prior models. +4. **Sampling parameters removed:** Setting `temperature`, `top_p`, or `top_k` to any non-default value on Claude Opus 4.7 or later models, including Claude Opus 5, returns a 400 error. The Python SDK (v1.0 and later) does not define them, and passing them raises a `TypeError`. The safest migration path is to omit these parameters entirely from request payloads. Prompting is the recommended way to guide model behavior on Claude Opus 5. If you were using `temperature = 0` for determinism, note that it never guaranteed identical outputs on prior models. 5. **Thinking content omitted by default:** Thinking blocks still appear in the response stream on Claude Opus 4.7 and later models, but their `thinking` field is empty unless you explicitly opt in. This is a silent change from Claude Opus 4.6, where the default was to return summarized thinking text. To restore summarized thinking content, set `thinking.display` to `"summarized"`:
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``` </CodeGroup> - Note that the migration also moves from `client.beta.messages.create` to `client.messages.create`. Adaptive thinking and effort are GA features and do not require the beta SDK namespace or any beta headers. + Note that the migration also moves from `client.beta.messages.create` to `client.messages.create`. Adaptive thinking and effort do not require the beta SDK namespace or any beta headers. -2. **Remove effort beta header:** The effort parameter is now GA. Remove `betas=["effort-2025-11-24"]` from your requests. +2. **Remove effort beta header:** The effort parameter does not require a beta header. Remove `betas=["effort-2025-11-24"]` from your requests. -3. **Remove fine-grained tool streaming beta header:** Fine-grained tool streaming is now GA. Remove `betas=["fine-grained-tool-streaming-2025-05-14"]` from your requests. +3. **Remove fine-grained tool streaming beta header:** Fine-grained tool streaming does not require a beta header. Remove `betas=["fine-grained-tool-streaming-2025-05-14"]` from your requests. 4. **Remove interleaved thinking beta header:** Adaptive thinking automatically enables interleaved thinking on Claude Opus 4.7, Opus 4.6, and Sonnet 4.6. Remove `betas=["interleaved-thinking-2025-05-14"]` from your requests. The header is still functional on Sonnet 4.6 with manual extended thinking, but manual mode is deprecated. -5. **Migrate to output\_config.format:** If using structured outputs, update `output_format={...}` to `output_config={"format": {...}}`. The old parameter remains functional but is deprecated and will be removed in a future model release. +5. **Migrate to output\_config.format:** If using structured outputs, update `output_format={...}` to `output_config={"format": {...}}`. The API still accepts the deprecated `output_format` parameter, but it will be removed in a future model release. The Python SDK (v1.0 and later) does not accept `output_format={...}` on `client.beta.messages.create()` or `count_tokens()`. The `output_format=Model` argument of the `parse()` and `stream()` helpers is unchanged. #### Migrating from Claude 4.1 or earlier
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This is a breaking change when migrating from Claude 3.x models. </Warning> - Starting with Claude Opus 4.7, setting `temperature`, `top_p`, or `top_k` to any non-default value returns a 400 error. The safest migration path is to omit these parameters entirely from requests, and to use prompting to guide the model's behavior. If you were using `temperature = 0` for determinism, note that it never guaranteed identical outputs. + Starting with Claude Opus 4.7, setting `temperature`, `top_p`, or `top_k` to any non-default value returns a 400 error. The Python SDK (v1.0 and later) does not define them, and passing them raises a `TypeError`. The safest migration path is to omit these parameters entirely from requests, and to use prompting to guide the model's behavior. If you were using `temperature = 0` for determinism, note that it never guaranteed identical outputs. <CodeGroup exclude="shell"> ```python Python
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* **BREAKING:** Remove assistant message prefills (returns 400 error); use structured outputs or `output_config.format` instead * **BREAKING on Opus 4.7:** Replace `thinking: {type: "enabled", budget_tokens: N}` with `thinking: {type: "adaptive"}` plus the [effort parameter](https://platform.claude.com/docs/en/build-with-claude/effort) (returns 400 on Opus 4.7) * Verify tool call JSON parsing uses a standard JSON parser -* Remove `effort-2025-11-24` beta header (effort is now GA) +* Remove `effort-2025-11-24` beta header (the effort parameter does not require it) * Remove `fine-grained-tool-streaming-2025-05-14` beta header * Remove `interleaved-thinking-2025-05-14` beta header (adaptive thinking enables interleaved thinking automatically) * Migrate `output_format` to `output_config.format` (if applicable)
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2. **Disabling thinking is capped at `high` effort:** On Claude Sonnet 5, `thinking: {type: "disabled"}` is accepted at any effort level. On Claude Opus 5, it is accepted only at an [effort](https://platform.claude.com/docs/en/build-with-claude/effort) level of `high` or below; a request that combines `thinking: {type: "disabled"}` with effort `xhigh` or `max` returns a 400 error, enforced on each request. Audit requests that disable thinking before you migrate. -3. **Mid-conversation system messages:** Claude Opus 5 accepts `role: "system"` messages immediately after a user turn in the `messages` array (subject to [placement rules](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages#limitations)); Claude Sonnet 5 does not. If you maintain code paths that rebuild the full message history to update instructions, you can simplify them and preserve [prompt cache](https://platform.claude.com/docs/en/build-with-claude/prompt-caching) hits on earlier turns. +3. **Mid-conversation system messages:** Claude Opus 5 accepts `role: "system"` messages immediately after a user turn in the `messages` array (subject to [placement rules](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages#limitations)). This feature is not available on Claude Sonnet 5; use the top-level `system` field instead. If you maintain code paths that rebuild the full message history to update instructions, you can simplify them and preserve [prompt cache](https://platform.claude.com/docs/en/build-with-claude/prompt-caching) hits on earlier turns. 4. **Web fetch is not available:** The [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) tool is available on Claude Sonnet 5 but not on Claude Opus 5.
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Claude Sonnet 5 offers the best combination of speed and intelligence in the Claude model family. It builds on Claude Sonnet 4.6. -Claude Sonnet 5 is a drop-in upgrade for Claude Sonnet 4.6, priced at $2/$10 USD per million input/output tokens; see [Pricing](https://platform.claude.com/docs/en/about-claude/pricing) for details. There are two breaking API changes for code already running on Claude Sonnet 4.6: manual extended thinking (`thinking: {type: "enabled", budget_tokens: N}`) and sampling parameters (`temperature`, `top_p`, `top_k`) set to non-default values are no longer accepted and return a 400 error. Use [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) with the [effort parameter](https://platform.claude.com/docs/en/build-with-claude/effort) instead. Claude Sonnet 5 supports the same set of features as Claude Sonnet 4.6, including the [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows), [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching), [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and the full set of server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview). On the Claude API, Claude Sonnet 5 also supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the generally available `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages, neither of which Claude Sonnet 4.6 supports; existing integrations on the earlier `computer_20251124` version continue to work unchanged on both models. To upgrade an existing integration, see [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not available on Claude Sonnet 5. Claude Sonnet 5 also uses a new tokenizer. +Claude Sonnet 5 is a drop-in upgrade for Claude Sonnet 4.6, priced at $2/$10 USD per million input/output tokens; see [Pricing](https://platform.claude.com/docs/en/about-claude/pricing) for details. There are two breaking API changes for code already running on Claude Sonnet 4.6: manual extended thinking (`thinking: {type: "enabled", budget_tokens: N}`) and sampling parameters (`temperature`, `top_p`, `top_k`) set to non-default values are no longer accepted and return a 400 error. Use [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) with the [effort parameter](https://platform.claude.com/docs/en/build-with-claude/effort) instead. Claude Sonnet 5 supports the same set of features as Claude Sonnet 4.6, including the [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows), [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching), [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and the full set of server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview). On the Claude API, Claude Sonnet 5 also supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the stable `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages, neither of which Claude Sonnet 4.6 supports; existing integrations on the earlier `computer_20251124` version continue to work unchanged on both models. To upgrade an existing integration, see [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not available on Claude Sonnet 5. Claude Sonnet 5 also uses a new tokenizer. ### Migrating to Claude Sonnet 5 from Claude Sonnet 4.6
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``` ```bash CLI - ant messages create \ - --transform content --format yaml <<'YAML' + ant messages create --transform content --format yaml <<'YAML' model: claude-sonnet-5 max_tokens: 16000 thinking:
about-claude/models/migration-guide Changed · +3 / -3 lines
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### Migrating to Claude Opus 5 from Claude Opus 4.7 -Claude Opus 5 should have strong out-of-the-box performance on existing Claude Opus 4.7 prompts and evals, at the same pricing of $5 per million input tokens and $25 per million output tokens. It supports the same set of features as Claude Opus 4.7, including the [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows), [128k max output tokens](https://platform.claude.com/docs/en/about-claude/models/overview), [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching), [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview), with two exceptions: [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) is not available on Claude Opus 5, and [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not supported on Claude Opus 5. It also adds [mid-conversation system messages](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages) and publicly documents [refusal stop details](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback#refusal-response). +Claude Opus 5 should have strong out-of-the-box performance on existing Claude Opus 4.7 prompts and evals, at the same pricing of $5 per million input tokens and $25 per million output tokens. It supports the same set of features as Claude Opus 4.7, including the [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows), [128k max output tokens](https://platform.claude.com/docs/en/about-claude/models/overview), [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching), [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview), with two exceptions: [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) is not available on Claude Opus 5, and [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not supported on Claude Opus 5. It also adds [mid-conversation system messages](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages) and publicly documents [refusal stop details](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback#refusal-response). On the Claude API, Claude Opus 5 also supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the generally available `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages, neither of which Claude Opus 4.7 supports; existing integrations on the earlier `computer_20251124` version continue to work unchanged on both models. To upgrade an existing integration, see [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). <Note> If your code is on Claude Opus 4.6 or earlier, use [Migrating to Claude Opus 5 from Claude Opus 4.6 and earlier Opus models](https://platform.claude.com/docs/en/about-claude/models/migration-guide#migrating-from-claude-opus-46) instead. That section includes breaking changes (sampling parameters rejected, manual extended thinking rejected, new tokenizer) that the upgrade from Claude Opus 4.7 alone does not cover.
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* [Vision](https://platform.claude.com/docs/en/build-with-claude/vision) * Server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview) ([bash](https://platform.claude.com/docs/en/agents-and-tools/tool-use/bash-tool), [code execution](https://platform.claude.com/docs/en/agents-and-tools/tool-use/code-execution-tool), [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool), [text editor](https://platform.claude.com/docs/en/agents-and-tools/tool-use/text-editor-tool), [web search](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-search-tool), [MCP connector](https://platform.claude.com/docs/en/agents-and-tools/mcp-connector), [memory](https://platform.claude.com/docs/en/agents-and-tools/tool-use/memory-tool)) -Two exceptions: [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) is not available on Claude Opus 5, and [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not supported on Claude Opus 5. +Two exceptions: [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool) is not available on Claude Opus 5, and [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not supported on Claude Opus 5. On the Claude API, Claude Opus 5 also supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the generally available `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages, neither of which Claude Opus 4.6 or earlier Opus models support; existing integrations on the earlier `computer_20251124` version continue to work unchanged on Claude Opus 5. To upgrade an existing integration, see [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). #### Update your model name
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Claude Sonnet 5 offers the best combination of speed and intelligence in the Claude model family. It builds on Claude Sonnet 4.6. -Claude Sonnet 5 is a drop-in upgrade for Claude Sonnet 4.6, priced at $2/$10 USD per million input/output tokens; see [Pricing](https://platform.claude.com/docs/en/about-claude/pricing) for details. There are two breaking API changes for code already running on Claude Sonnet 4.6: manual extended thinking (`thinking: {type: "enabled", budget_tokens: N}`) and sampling parameters (`temperature`, `top_p`, `top_k`) set to non-default values are no longer accepted and return a 400 error. Use [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) with the [effort parameter](https://platform.claude.com/docs/en/build-with-claude/effort) instead. Claude Sonnet 5 supports the same set of features as Claude Sonnet 4.6, including the [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows), [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching), [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and the full set of server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview). [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not available on Claude Sonnet 5. Claude Sonnet 5 also uses a new tokenizer. +Claude Sonnet 5 is a drop-in upgrade for Claude Sonnet 4.6, priced at $2/$10 USD per million input/output tokens; see [Pricing](https://platform.claude.com/docs/en/about-claude/pricing) for details. There are two breaking API changes for code already running on Claude Sonnet 4.6: manual extended thinking (`thinking: {type: "enabled", budget_tokens: N}`) and sampling parameters (`temperature`, `top_p`, `top_k`) set to non-default values are no longer accepted and return a 400 error. Use [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) with the [effort parameter](https://platform.claude.com/docs/en/build-with-claude/effort) instead. Claude Sonnet 5 supports the same set of features as Claude Sonnet 4.6, including the [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows), [adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching), [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and the full set of server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview). On the Claude API, Claude Sonnet 5 also supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the generally available `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages, neither of which Claude Sonnet 4.6 supports; existing integrations on the earlier `computer_20251124` version continue to work unchanged on both models. To upgrade an existing integration, see [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is not available on Claude Sonnet 5. Claude Sonnet 5 also uses a new tokenizer. ### Migrating to Claude Sonnet 5 from Claude Sonnet 4.6
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To increase tool usage, raise the effort setting. `high` or `xhigh` effort settings show substantially more tool usage in agentic search and coding. You can also adjust your prompt to explicitly instruct the model about when and how to properly use its tools. -8. **Real-time cybersecurity safeguards:** Newly added in Claude Opus 4.7, requests that involve prohibited or high-risk topics may lead to refusals. For legitimate security work such as penetration testing, vulnerability research, or red-teaming, apply to the [Cyber Verification Program](https://claude.com/form/cyber-use-case) to request reduced restrictions. See [Safeguards, warnings, and appeals](https://support.claude.com/en/articles/8241253-safeguards-warnings-and-appeals) for background. +8. **Real-time cybersecurity safeguards:** Newly added in Claude Opus 4.7, requests that involve prohibited or high-risk topics may lead to refusals. For legitimate security work such as penetration testing, vulnerability research, or red-teaming, apply to the [Cyber Verification Program](https://support.claude.com/en/articles/14604842-real-time-cyber-safeguards-on-claude-opus-and-sonnet) to request reduced restrictions. The application route depends on how you access Claude. 9. **High-resolution image support:** Claude Opus 4.7 is the first Claude model with high-resolution image support. Maximum image resolution is 2,576 pixels on the long edge, up from 1,568 pixels on prior models. This unlocks gains on vision-heavy workloads and is particularly valuable for computer use, screenshot understanding, and document analysis.
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* If you use [web fetch](https://platform.claude.com/docs/en/agents-and-tools/tool-use/web-fetch-tool), plan an alternative: it is not available on Claude Opus 5. * If your organization has a [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) commitment, note that Priority Tier is not supported on Claude Opus 5. * Remove verification and self-check instructions carried over from prompts tuned for earlier models; they cause over-verification on Claude Opus 5. -* If your product does legitimate security work, apply to the [Cyber Verification Program](https://claude.com/form/cyber-use-case) for access to lower restrictions on cyber content. +* If your product does legitimate security work, apply to the [Cyber Verification Program](https://support.claude.com/en/articles/14604842-real-time-cyber-safeguards-on-claude-opus-and-sonnet) for access to lower restrictions on cyber content. #### Migrating from Claude Opus 4.5 or earlier
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5. **Sampling parameters removed:** Sampling parameters (`temperature`, `top_p`, `top_k`) set to a non-default value are not accepted and return a 400 error. -6. **Cybersecurity safeguards:** Claude Sonnet 5 is the first Sonnet-tier model with real-time cybersecurity safeguards. Requests that involve prohibited or high-risk cybersecurity topics may be refused. Refusals return as a successful HTTP 200 response with `stop_reason: "refusal"`, not an error. See [Safeguards, warnings, and appeals](https://support.claude.com/en/articles/8241253-safeguards-warnings-and-appeals) for background. +6. **Cybersecurity safeguards:** Claude Sonnet 5 is the first Sonnet-tier model with real-time cybersecurity safeguards. Requests that involve prohibited or high-risk cybersecurity topics may be refused. Refusals return as a successful HTTP 200 response with `stop_reason: "refusal"`, not an error. See [Real-time cyber safeguards on Claude Opus and Sonnet](https://support.claude.com/en/articles/14604842-real-time-cyber-safeguards-on-claude-opus-and-sonnet) for what the safeguards block and how legitimate security work can apply to the Cyber Verification Program. #### Migration checklist
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5. **Pricing:** Claude Haiku 4.5 is priced at $1/$5 per million input/output tokens. Claude Sonnet 5 is priced at $2/$10 per million input/output tokens. See [Claude pricing](https://platform.claude.com/docs/en/about-claude/pricing). -6. **Cybersecurity safeguards:** Claude Sonnet 5 has real-time cybersecurity safeguards. Requests that involve prohibited or high-risk cybersecurity topics may be refused, returned as a successful HTTP 200 response with `stop_reason: "refusal"`. See [Safeguards, warnings, and appeals](https://support.claude.com/en/articles/8241253-safeguards-warnings-and-appeals) for background. +6. **Cybersecurity safeguards:** Claude Sonnet 5 has real-time cybersecurity safeguards. Requests that involve prohibited or high-risk cybersecurity topics may be refused, returned as a successful HTTP 200 response with `stop_reason: "refusal"`. See [Real-time cyber safeguards on Claude Opus and Sonnet](https://support.claude.com/en/articles/14604842-real-time-cyber-safeguards-on-claude-opus-and-sonnet) for what the safeguards block and how legitimate security work can apply to the Cyber Verification Program. #### Migration checklist
about-claude/models/migration-guide First recorded · 2772 lines, first recorded
## Migrating to Claude Mythos 5 and Claude Fable 5 ### Migrating to Claude Mythos 5 and Claude Fable 5 from Claude Mythos Preview #### Update your model name #### Features not available on Claude Mythos 5 and Claude Fable 5 #### Token counting and billing #### Migration checklist ### Migrating to Claude Mythos 5 and Claude Fable 5 from Claude Opus 5 #### Update your model name #### What changed #### Migration checklist ### Migrating to Claude Mythos 5 and Claude Fable 5 from Claude Opus 4.8 #### Update your model name #### What changed #### Migration checklist ## Migrating to Claude Opus 5 ### Migrating to Claude Opus 5 from Claude Opus 4.8 #### Update your model name #### Breaking changes #### Recommended changes #### Migration checklist ### Migrating to Claude Opus 5 from Claude Opus 4.7 #### Update your model name #### Breaking changes #### What changed #### Recommended changes #### Migration checklist ### Migrating to Claude Opus 5 from Claude Opus 4.6 and earlier Opus models #### Update your model name #### Breaking changes #### Choosing an effort level #### Behavior changes #### Recommended changes #### Migration checklist #### Migrating from Claude Opus 4.5 or earlier ##### Update your model name ##### Breaking changes ##### Recommended changes #### Migrating from Claude 4.1 or earlier ##### Additional breaking changes ##### Additional recommended changes #### Migration checklist (from Claude Opus 4.5 or earlier) ### Migrating to Claude Opus 5 from Claude Sonnet 5 #### Update your model name #### What changed #### Migration checklist ## Migrating to Claude Sonnet 5 ### Migrating to Claude Sonnet 5 from Claude Sonnet 4.6 #### Update your model name #### What changed #### Migration checklist ### Migrating to Claude Sonnet 5 from Claude Sonnet 4.5 and earlier Sonnet models #### Breaking changes ##### When migrating from Sonnet 4.5 ##### When migrating from Claude 3.x ### Migrating to Claude Sonnet 5 from Claude Haiku 4.5 #### Update your model name #### What changed #### Migration checklist ## Migrating to Claude Haiku 4.5 ### Migrating to Claude Haiku 4.5 from Claude Haiku 3.5 and earlier Haiku models #### Breaking changes #### Haiku 4.5 migration checklist ## Get help
The first capture of this source. The page was already there, and this is what it said.
---
title: Migration guide
url: https://platform.claude.com/docs/en/about-claude/models/migration-guide
description: Guide for migrating to the latest Claude models from previous Claude versions
---
<Note>
This guide covers migrating [Messages API](https://platform.claude.com/docs/en/build-with-claude/working-with-messages) code. If you use [Claude Managed Agents](https://platform.claude.com/docs/en/managed-agents/overview), no changes beyond updating the model name are required.
</Note>
<Tip>
**Automate your migration with the Claude API skill.** In Claude Code, run `/claude-api migrate` to invoke the bundled [Claude API skill](https://platform.claude.com/docs/en/agents-and-tools/agent-skills/claude-api-skill#migrating-to-a-newer-claude-model). It works for any target model on this page:
```text wrap
/claude-api migrate this project to claude-opus-5
```
The skill applies the model ID swap and, as needed, breaking parameter changes, prefill replacement, and effort calibration for your target model across your code base, then produces a checklist of items to verify manually. It asks you to confirm the migration scope (entire working directory, a subdirectory, or a specific file list) before editing any files. The skill also detects Amazon Bedrock and Claude Platform on AWS clients and adjusts model ID formats and feature changes for those platforms.
</Tip>
## Migrating to Claude Mythos 5 and Claude Fable 5
[Claude Fable 5](https://platform.claude.com/docs/en/about-claude/models/introducing-claude-fable-5-and-claude-mythos-5) is Anthropic's most capable widely released model, generally available on the Claude API, [Amazon Bedrock](https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock), [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), [Google Cloud](https://platform.claude.com/docs/en/build-with-claude/claude-on-vertex-ai), and [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry). [Claude Mythos 5](https://anthropic.com/glasswing) shares the same capabilities and is offered in limited availability to approved customers in Project Glasswing.
The baseline settings shared by `claude-fable-5` and `claude-mythos-5`:
* **Thinking:** [Adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) is always on. The model determines when and how much to think on each request, and no `thinking` configuration is required. Both `thinking: {type: "disabled"}` and manual extended thinking (`thinking: {type: "enabled", budget_tokens: N}`) return a 400 error.
* **Prefill:** Prefilling the assistant message returns a 400 error. Use system prompt instructions instead.
* **Context window and output:** A [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) by default, and up to 128k output tokens per request.
* **Pricing:** $10 USD per million input tokens and $50 USD per million output tokens. See [Claude pricing](https://platform.claude.com/docs/en/about-claude/pricing).
* **Data retention:** Both models require 30-day data retention and are not available under zero data retention (ZDR) arrangements; both are designated Covered Models. On the Claude API, a request to Claude Fable 5 from an organization whose data retention configuration does not meet this requirement returns a 400 `invalid_request_error`. Organizations with a ZDR arrangement should contact their Anthropic account team to discuss data retention configuration. Alternatively, you can configure data retention per workspace. See [Model-specific data retention requirements](https://platform.claude.com/docs/en/manage-claude/api-and-data-retention#model-specific-data-retention-requirements) for per-platform details.
Where the two models diverge:
* **Availability:** Claude Fable 5 is generally available. Claude Mythos 5 is available only to approved customers in [Project Glasswing](https://anthropic.com/glasswing).
* **Safety classifiers:** Claude Fable 5 runs safety classifiers that can decline requests with `stop_reason: "refusal"`. Claude Mythos 5 does not include these classifiers. See [Refusals and fallback](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback).
* **Priority Tier:** [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers#supported-models) is supported on Claude Fable 5 but not on Claude Mythos 5.
### Migrating to Claude Mythos 5 and Claude Fable 5 from Claude Mythos Preview
[Claude Mythos 5](https://anthropic.com/glasswing) is the access-gated successor to [Claude Mythos Preview](https://anthropic.com/glasswing), the invitation-only research preview. [Claude Fable 5](https://platform.claude.com/docs/en/about-claude/models/introducing-claude-fable-5-and-claude-mythos-5) is the generally available model with the same capabilities, and the changes in this section apply equally to both targets.
Migration is mostly drop-in. Claude Mythos 5 and Claude Fable 5 use the same [Messages API](https://platform.claude.com/docs/en/build-with-claude/working-with-messages) and the same [tool use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview) patterns as Claude Mythos Preview, and token counts are roughly unchanged because all three models use the same tokenizer. The key changes to check are the features that are no longer available (listed in the next section) and thinking output. If you migrate to Claude Fable 5, also plan for safety classifier refusals, which Claude Mythos Preview and Claude Mythos 5 do not have; see [Refusals and fallback](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback).
For the Claude Mythos Preview retirement timeline, see [Model deprecations](https://platform.claude.com/docs/en/about-claude/model-deprecations).
#### Update your model name
```python
model = "claude-mythos-preview" # Before
model = "claude-mythos-5" # After
# Or, for the generally available model with the same capabilities:
model = "claude-fable-5" # After
```
#### Features not available on Claude Mythos 5 and Claude Fable 5
1. **Extended thinking and thinking token budgets:** Manual extended thinking (`thinking: {type: "enabled", budget_tokens: N}`) is not supported on `claude-mythos-5` or `claude-fable-5` and returns a 400 error. [Adaptive thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) is always on: the model determines when and how much to think on each request, and no `thinking` configuration is required. `thinking: {type: "disabled"}` returns an error. `budget_tokens` has no direct replacement: thinking is adaptive, and the [effort parameter](https://platform.claude.com/docs/en/build-with-claude/effort) is a separate output-level control, not a thinking budget.
Before (Claude Mythos Preview):
<CodeGroup>
```bash cURL
curl https://api.anthropic.com/v1/messages \
-H "x-api-key: $ANTHROPIC_API_KEY" \
-H "anthropic-version: 2023-06-01" \
-H "content-type: application/json" \
-d '{
"model": "claude-mythos-preview",
"max_tokens": 16000,
"thinking": {
"type": "enabled",
"budget_tokens": 10000
},
"messages": [
{
"role": "user",
"content": "..."
}
]
}'
```
```bash CLI
ant messages create <<'YAML'
model: claude-mythos-preview
max_tokens: 16000
thinking:
type: enabled
budget_tokens: 10000
messages:
- role: user
content: "..."
YAML
```
```python Python
client.messages.create(
model="claude-mythos-preview",
max_tokens=16000,
thinking={"type": "enabled", "budget_tokens": 10000},
messages=[{"role": "user", "content": "..."}],
)
```
```typescript TypeScript
await client.messages.create({
model: "claude-mythos-preview",
max_tokens: 16000,
thinking: { type: "enabled", budget_tokens: 10000 },
messages: [{ role: "user", content: "..." }]
});
```
```csharp C#
using Anthropic;
using Anthropic.Models.Messages;
AnthropicClient client = new();
var parameters = new MessageCreateParams
{
Model = "claude-mythos-preview",
MaxTokens = 16000,
Thinking = new ThinkingConfigEnabled(budgetTokens: 10000),
Messages = [new() { Role = Role.User, Content = "..." }]
};
var response = await client.Messages.Create(parameters);
Console.WriteLine(response);
```
```go Go
client := anthropic.NewClient()
response, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
Model: "claude-mythos-preview",
MaxTokens: 16000,
Thinking: anthropic.ThinkingConfigParamOfEnabled(10000),
Messages: []anthropic.MessageParam{
anthropic.NewUserMessage(anthropic.NewTextBlock("...")),
},
})
if err != nil {
log.Fatal(err)
}
fmt.Println(response)
```
```java Java
AnthropicClient client = AnthropicOkHttpClient.fromEnv();
MessageCreateParams params = MessageCreateParams.builder()
.model("claude-mythos-preview")
.maxTokens(16000L)
.enabledThinking(10000L)
.addUserMessage("...")
.build();
Message response = client.messages().create(params);
IO.println(response);
```
```php PHP
$client = new Client();
$message = $client->messages->create(
maxTokens: 16000,
messages: [['role' => 'user', 'content' => '...']],
model: 'claude-mythos-preview',
thinking: ['type' => 'enabled', 'budget_tokens' => 10000],
);
```
```ruby Ruby
client = Anthropic::Client.new
message = client.messages.create(
model: "claude-mythos-preview",
max_tokens: 16000,
thinking: {
type: "enabled",
budget_tokens: 10000
},
messages: [
{ role: "user", content: "..." }
]
)
```
</CodeGroup>
After (Claude Mythos 5):
<CodeGroup>
```bash cURL
curl https://api.anthropic.com/v1/messages \
-H "x-api-key: $ANTHROPIC_API_KEY" \
-H "anthropic-version: 2023-06-01" \
-H "content-type: application/json" \
-d '{
"model": "claude-mythos-5",
"max_tokens": 16000,
"messages": [
{
"role": "user",
"content": "..."
}
]
}'
```
```bash CLI
ant messages create <<'YAML'
model: claude-mythos-5
max_tokens: 16000
messages:
- role: user
content: "..."
YAML
```
```python Python
client.messages.create(
model="claude-mythos-5",
max_tokens=16000,
messages=[{"role": "user", "content": "..."}],
)
```
```typescript TypeScript
await client.messages.create({
model: "claude-mythos-5",
max_tokens: 16000,
messages: [{ role: "user", content: "..." }]
});
```
```csharp C#
using Anthropic;
using Anthropic.Models.Messages;
AnthropicClient client = new();
var parameters = new MessageCreateParams
{
Model = "claude-mythos-5",
MaxTokens = 16000,
Messages = [new() { Role = Role.User, Content = "..." }]
};
var response = await client.Messages.Create(parameters);
Console.WriteLine(response);
```
```go Go
client := anthropic.NewClient()
response, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
Model: "claude-mythos-5",
MaxTokens: 16000,
Messages: []anthropic.MessageParam{
anthropic.NewUserMessage(anthropic.NewTextBlock("...")),
},
})
if err != nil {
log.Fatal(err)
}
fmt.Println(response)
```
```java Java
AnthropicClient client = AnthropicOkHttpClient.fromEnv();
MessageCreateParams params = MessageCreateParams.builder()
.model("claude-mythos-5")
.maxTokens(16000L)
.addUserMessage("...")
.build();
Message response = client.messages().create(params);
IO.println(response);
```
```php PHP
$client = new Client();
$message = $client->messages->create(
maxTokens: 16000,
messages: [['role' => 'user', 'content' => '...']],
model: 'claude-mythos-5',
);
```
```ruby Ruby
client = Anthropic::Client.new
message = client.messages.create(
model: "claude-mythos-5",
max_tokens: 16000,
Cut at 300 lines.