whats-new-fable-5-2 changedmodels/fable-5-2/whats-new-fable-5-2
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6363
6464### Use the computer use toolset instead of `computer_20251124`
6565
66Claude Fable 5.1 accepts [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) both as the `computer_toolset_20260801` toolset and, with the `computer-use-2025-11-24` beta header, as the earlier `computer_20251124` tool. Claude Fable 5.2 and Claude Mythos 5.2 support computer use through the toolset. A request to either model that declares a `computer_20251124` tool returns a 400 `invalid_request_error` on every platform except Amazon Bedrock, where the earlier tool works as it does on Claude Fable 5.1.
66Claude Fable 5.1 accepts [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) both as the `computer_toolset_20260801` toolset and, with the `computer-use-2025-11-24` beta header, as the earlier `computer_20251124` tool. Claude Fable 5.2 and Claude Mythos 5.2 support computer use through the toolset. A request to either model that declares a `computer_20251124` tool returns a 400 `invalid_request_error` on every platform except Amazon Bedrock. There, both models accept the earlier tool: with the InvokeModel API, send `computer-use-2025-11-24` in the `anthropic_beta` array of the request body.
6767
6868To move an existing integration, follow [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124).
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8787* **Effort:** all five [effort levels](https://platform.claude.com/docs/en/build-with-claude/effort#effort-levels): `low`, `medium`, `high`, `xhigh`, and `max`. The API default is `high`. Start there, because most of the gain in capability is already present at `high`. Step up to `xhigh` for your hardest long-running coding and agentic work, where you’ve measured a gain. Reserve `max` for measuring the model’s ceiling and for the rare task where time and tokens don’t matter. See [Recommended effort levels for Claude Fable 5.2](https://platform.claude.com/docs/en/build-with-claude/effort#recommended-effort-levels-for-claude-fable-5-2).
8888* **Compaction on demand (beta):** with the `compact-2026-09-04` beta header, you choose when to replace older turns with a summary. See [Compaction on demand](https://platform.claude.com/docs/en/build-with-claude/compaction-on-demand).
8989* **Mid-conversation tool changes (beta):** you add or remove tools in a `role: "system"` message instead of editing `tools`. On the Claude API, Claude Platform on AWS, and Claude Models on Google Cloud (Anthropic managed), send the `inline-tools-2026-09-15` beta header. The `mid-conversation-tool-changes-2026-07-01` header works for changes that name a tool by reference, on the platforms that [Mid-conversation system messages and tool changes](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages) lists. See [Mid-conversation tool changes](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages#mid-conversation-tool-changes).
90* **Computer use:** through the `computer_toolset_20260801` toolset. The earlier `computer_20251124` tool returns a 400 error on every platform except Amazon Bedrock, where both models also accept the earlier tool (see the [computer use breaking change](https://platform.claude.com/docs/en/models/fable-5-2/whats-new-fable-5-2#computer-20251124-is-not-supported)). See [Computer use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool).
90* **Computer use:** through the `computer_toolset_20260801` toolset. The earlier `computer_20251124` tool returns a 400 error on every platform except Amazon Bedrock. There, Claude Fable 5.2 and Claude Mythos 5.2 also accept the earlier tool. See the [computer use breaking change](https://platform.claude.com/docs/en/models/fable-5-2/whats-new-fable-5-2#computer-20251124-is-not-supported) and [Computer use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool).
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9292Compaction on demand and mid-conversation tool changes help you keep the history append-only, which the [prefix check](https://platform.claude.com/docs/en/models/fable-5-2/whats-new-fable-5-2#editing-earlier-turns-invalidates-thinking-blocks) requires. See each feature’s page for model and platform availability.
9393
94[Fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) is available for Claude Fable 5.2 in Messages API requests on the Claude API.
94[Fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) is available for Claude Fable 5.2 in Messages API requests on the Claude API, [Claude Models on Google Cloud (Anthropic managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/anthropic-managed), [Claude Models on Google Cloud (Google managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/google-managed), and [Claude in Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry). On Claude in Microsoft Foundry, it’s available for deployments hosted on Anthropic, with its own model ID, `claude-fable-5-2-fast`.
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96Fast mode is also available for Claude Fable 5.2 on [Claude Models on Google Cloud (Anthropic managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/anthropic-managed).
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98Fast mode is also available for Claude Fable 5.2 on [Claude Models on Google Cloud (Google managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/google-managed).
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100Fast mode is also available for Claude Fable 5.2 on [Claude in Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry) for deployments hosted on Anthropic, as a separate model, `claude-fable-5-2-fast`.
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10296Fast mode is also available for Claude Mythos 5.2 in Messages API requests on the Claude API. [Availability of fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode#feature-availability) lists every platform where Claude Mythos 5.2 has fast mode.
10397
10498### Thinking blocks stay with the account that produced them
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114108* **What the prompt says about code ownership matters.** In Anthropic’s testing on small coding tasks, when a prompt said nothing about who owns the code, the model tended to add to the existing structure and to report nearby problems instead of fixing them. See [Say who owns the code](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-fable-5-2#say-who-owns-the-code).
115109* **Long runs of tool calls can pass with little user-facing text.** The model might also make its first tool call without saying what it’s about to do. See [Keep users informed during long turns](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-fable-5-2#keep-users-informed-during-long-turns).
116110* **How much the model delegates to subagents depends on your harness and tasks.** In an agentic coding product whose prompts invite delegation, the model delegates readily. Subagents can account for a large part of what a session costs. See [Set expectations for subagents](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-fable-5-2#set-expectations-for-subagents).
117* **The model follows style rules closely.** A hard limit on sentence length can make the model’s prose choppy. See [Review instructions written for earlier models](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-fable-5-2#review-instructions-written-for-earlier-models).
111* **The model follows style rules closely.** A hard limit on sentence length can make the model’s prose choppy. See [Review prompts and harnesses designed for earlier models](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-fable-5-2#review-instructions-written-for-earlier-models).
118112
119113## Refusals, fallback, and billing
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132126| ---------- | --------------- | --------------- | ------------ | ---------- |
133127| $8 / MTok | $10 / MTok | $16 / MTok | $0.20 / MTok | $40 / MTok |
134128
135Input and output cost less than on Claude Fable 5.1 and Claude Mythos 5.1, which cost $10 USD per million input tokens and $50 USD per million output tokens. Cache reads (hits and refreshes) cost 0.025 times the base input price, the same multiplier as on those models. [Batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing) is $4 USD per million input tokens and $20 USD per million output tokens. [Fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) for Claude Fable 5.2 costs $16 USD per million input tokens and $80 USD per million output tokens. See [Fast mode pricing](https://platform.claude.com/docs/en/about-claude/pricing#fast-mode-pricing). Fast mode for Claude Mythos 5.2 costs $16 USD per million input tokens and $80 USD per million output tokens. See [Pricing](https://platform.claude.com/docs/en/about-claude/pricing) for data residency and tool pricing.
129Input and output cost less than on Claude Fable 5.1 and Claude Mythos 5.1. Claude Fable 5.1 and Claude Mythos 5.1 cost $10 USD per million input tokens and $50 USD per million output tokens. Cache reads (hits and refreshes) cost 0.025 times the base input price, the same multiplier as on those models. [Batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing) is $4 USD per million input tokens and $20 USD per million output tokens. [Fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) for Claude Fable 5.2 and Claude Mythos 5.2 costs $16 USD per million input tokens and $80 USD per million output tokens. See [Fast mode pricing](https://platform.claude.com/docs/en/about-claude/pricing#fast-mode-pricing). See [Pricing](https://platform.claude.com/docs/en/about-claude/pricing) for data residency and tool pricing.
136130
137131## Availability
138132
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139133Claude Fable 5.2 is available on:
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141135* **Claude API:** all customers, as `claude-fable-5-2`
142* **AWS:** [Claude in Amazon Bedrock](https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock), as `anthropic.claude-fable-5-2`, and [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), as `claude-fable-5-2`
136* **AWS:** [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), as `claude-fable-5-2`
137* **Amazon Bedrock:** `global.anthropic.claude-fable-5-2` or `us.anthropic.claude-fable-5-2`, on the [`bedrock-runtime` endpoint](https://platform.claude.com/docs/en/build-with-claude/claude-on-amazon-bedrock-legacy#api-model-ids) only
143138* **Google Cloud:** [Claude Models on Google Cloud (Anthropic managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/anthropic-managed), as `claude-fable-5-2`, and [Claude Models on Google Cloud (Google managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/google-managed), as `claude-fable-5-2`
144139* **Microsoft Foundry:** [Claude in Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry), as `claude-fable-5-2`, on Anthropic infrastructure (see [Hosting options](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry#hosting-options))
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146141Claude Mythos 5.2 is available only to organizations verified through Anthropic’s verification programs, such as the [Cyber Verification Program](https://support.claude.com/en/articles/14604842). It’s available on:
147142
148143* **Claude API:** as `claude-mythos-5-2`
149* **AWS:** [Claude in Amazon Bedrock](https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock), as `anthropic.claude-mythos-5-2`
144* **Amazon Bedrock:** `global.anthropic.claude-mythos-5-2` or `us.anthropic.claude-mythos-5-2`, on the [`bedrock-runtime` endpoint](https://platform.claude.com/docs/en/build-with-claude/claude-on-amazon-bedrock-legacy#api-model-ids) only
150145* **Google Cloud:** [Claude Models on Google Cloud (Anthropic managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/anthropic-managed), as `claude-mythos-5-2`, and [Claude Models on Google Cloud (Google managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/google-managed), as `claude-mythos-5-2`
151146* **Microsoft Foundry:** [Claude in Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry), as `claude-mythos-5-2`, on Anthropic infrastructure
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