30| Model alias | Behavior |30| Model alias | Behavior |
31| - | - |31| - | - |
32| **`default`** | Special value that clears any model override and reverts to the [runtime default for your account](#default-model-setting). Not itself a model alias |32| **`default`** | Special value that clears any model override and reverts to the [runtime default for your account](#default-model-setting). Not itself a model alias |
33| **`best`** | Uses the model the [`fable` alias resolves to](#fable-alias-resolution) where Fable is available to you, otherwise the same model as `opus` |33| **`best`** | Uses the same model as `opus` |
34| **`fable`** | Uses the [Fable model for your provider](#fable-alias-resolution) for your hardest and longest-running tasks |34| **`fable`** | Uses the [Fable model for your provider](#fable-alias-resolution) for your hardest and longest-running tasks |
35| **`sonnet`** | Uses the latest Sonnet model for daily coding tasks |35| **`sonnet`** | Uses the latest Sonnet model for daily coding tasks |
36| **`opus`** | Uses the latest Opus model for complex reasoning tasks |36| **`opus`** | Uses the latest Opus model for complex reasoning tasks |
48| Amazon Bedrock, Google Cloud's Agent Platform | Opus 5.5 | Sonnet 4.5 | Haiku 4.5 |48| Amazon Bedrock, Google Cloud's Agent Platform | Opus 5.5 | Sonnet 4.5 | Haiku 4.5 |
49| Microsoft Foundry | Opus 4.6 | Sonnet 4.5 | Haiku 4.5 |49| Microsoft Foundry | Opus 4.6 | Sonnet 4.5 | Haiku 4.5 |
50 50
51Unless you set `ANTHROPIC_DEFAULT_FABLE_MODEL`, the `fable` alias resolves to Fable 5.1, except in [Claude apps gateway](https://code.claude.com/docs/en/claude-apps-gateway) sessions, where `fable` and `best` resolve to Fable 5.51Unless you set `ANTHROPIC_DEFAULT_FABLE_MODEL`, the `fable` alias resolves to Fable 5 in [Claude apps gateway](https://code.claude.com/docs/en/claude-apps-gateway) sessions and to Fable 5.2 everywhere else.
52 52
53A gateway that isn't configured to serve `claude-fable-5-1` rejects requests for that model. To use Fable 5.1 through a gateway that serves it, select it with `/model claude-fable-5-1`.53A gateway that isn't configured to serve `claude-fable-5-2` rejects requests for that model. To use Fable 5.2 through a gateway that serves it, select it with `/model claude-fable-5-2`.
54 54
55Where `opus` or `sonnet` resolves to an older model, newer models are available by selecting the full model name explicitly or setting `ANTHROPIC_DEFAULT_OPUS_MODEL` or `ANTHROPIC_DEFAULT_SONNET_MODEL`.55Where `opus` or `sonnet` resolves to an older model, newer models are available by selecting the full model name explicitly or setting `ANTHROPIC_DEFAULT_OPUS_MODEL` or `ANTHROPIC_DEFAULT_SONNET_MODEL`.
56 56
64 64
65### Work with Fable65### Work with Fable
66 66
67[Claude Fable 5.1](https://platform.claude.com/docs/en/about-claude/models/overview) and Claude Fable 5 are the most capable models in Claude Code, suited to tasks larger than a single sitting. They sustain long autonomous sessions, investigate before acting, and verify their work more often than smaller models. Fable 5.1 is the newer release.67[Claude Fable models](https://platform.claude.com/docs/en/about-claude/models/overview) are the most capable models in Claude Code, suited to tasks larger than a single sitting. They sustain long autonomous sessions, investigate before acting, and verify their work more often than smaller models.
68 68
69Neither Fable model is the account-type default on any plan or provider. Select one explicitly:69No Fable model is the account-type default on any plan or provider. Select one explicitly:
70 70
71* **Fable 5.1**: run `/model fable`, or launch with `claude --model fable`. In [Claude apps gateway](https://code.claude.com/docs/en/claude-apps-gateway) sessions, where the alias resolves to Fable 5, run `/model claude-fable-5-1` instead.71* **Fable 5.2**: run `/model fable`, or launch with `claude --model fable`. In [Claude apps gateway](https://code.claude.com/docs/en/claude-apps-gateway) sessions, run `/model claude-fable-5-2` instead.
72* **Fable 5**: select it by model ID. On the Anthropic API, run `/model claude-fable-5` or launch with `claude --model claude-fable-5`. On other providers, use your provider's Fable 5 model ID or [pin it](#pin-models-for-third-party-deployments) with `ANTHROPIC_DEFAULT_FABLE_MODEL`.72* **Fable 5.1 or Fable 5**: select it by model ID. On the Anthropic API, run `/model claude-fable-5-1` or `/model claude-fable-5`, or launch with `claude --model claude-fable-5-1`. On other providers, use your provider's model ID or [pin it](#pin-models-for-third-party-deployments) with `ANTHROPIC_DEFAULT_FABLE_MODEL`.
73 73
74If you connect to the Anthropic API directly and your user settings hold `claude-fable-5` or `claude-fable-5[1m]` as the model, for example because you selected Fable in the `/model` picker before v2.1.257, Claude Code changes that saved value to the `fable` or `fable[1m]` alias the first time you run v2.1.257 or later. The startup model line shows `(auto-updated)` once. A `claude-fable-5` value in project, local, or managed settings stays as it is.74On Pro, Max, Team, and Enterprise plans, a `claude-fable-5-1` model saved in your user settings moves to the `fable` alias:
75
76* **Pro or Max plan**: the move happens the first time you run v2.1.321 or later. In the terminal, the startup model line can show `(auto-updated)` once.
77* **Team or Enterprise plan**: the move waits for your organization's settings, so it can come at a later startup, or not at all. It applies from the next session, with no `(auto-updated)` line. To check your model, run `/model`.
78
79After the move, sessions start at Fable 5.2's default effort unless you've [set a level](#adjust-effort-level) for it. Console accounts, third-party providers, and project, local, or managed settings keep `claude-fable-5-1`.
75 80
76Requests that a Fable model's safety classifiers flag, most often in cybersecurity and biology domains, trigger [automatic model fallback](#automatic-model-fallback).81Requests that a Fable model's safety classifiers flag, most often in cybersecurity and biology domains, trigger [automatic model fallback](#automatic-model-fallback).
77 82
84 89
85> [!NOTE]90> [!NOTE]
86>91>
87> Fable 5.1 requires Claude Code v2.1.257 or later. If a request for it from an older version fails, see [Claude Code does not support this model](https://code.claude.com/docs/en/errors.md#claude-code-does-not-support-this-model). Run `claude update` to upgrade. For availability under zero data retention, see [Model availability under ZDR](https://code.claude.com/docs/en/zero-data-retention.md#model-availability-under-zdr).92> Fable 5.2 requires Claude Code v2.1.321 or later, and Fable 5.1 requires v2.1.257 or later. If a request for one of them from an older version fails, see [Claude Code does not support this model](https://code.claude.com/docs/en/errors.md#claude-code-does-not-support-this-model). Run `claude update` to upgrade. For availability under zero data retention, see [Model availability under ZDR](https://code.claude.com/docs/en/zero-data-retention.md#model-availability-under-zdr).
88 93
89On the Anthropic API, a Fable model appears in the `/model` picker unless [`availableModels`](#restrict-model-selection) or [organization model restrictions](#organization-model-restrictions) exclude it. When your organization can't use Fable at all, for example under [zero data retention](https://code.claude.com/docs/en/zero-data-retention.md#model-availability-under-zdr), the row stays in the picker grayed out, with a note on why.94On the Anthropic API, a Fable model appears in the `/model` picker unless [`availableModels`](#restrict-model-selection) or [organization model restrictions](#organization-model-restrictions) exclude it. When your organization can't use Fable at all, for example under [zero data retention](https://code.claude.com/docs/en/zero-data-retention.md#model-availability-under-zdr), the row stays in the picker grayed out, with a note on why.
90 95
163 168
164See [Model is not a recognized model id](https://code.claude.com/docs/en/errors.md#model-is-not-a-recognized-model-id) and [Model not found](https://code.claude.com/docs/en/errors.md#model-not-found) for the messages.169See [Model is not a recognized model id](https://code.claude.com/docs/en/errors.md#model-is-not-a-recognized-model-id) and [Model not found](https://code.claude.com/docs/en/errors.md#model-not-found) for the messages.
165 170
166If you set the model with the `--model` flag, the `ANTHROPIC_MODEL` environment variable, or the `model` setting, Claude Code doesn't check it up front, and a mistyped value produces [There's an issue with the selected model](https://code.claude.com/docs/en/errors.md#theres-an-issue-with-the-selected-model) on the first request.171If you set the model with the `--model` flag, the `ANTHROPIC_MODEL` environment variable, or the `model` setting, Claude Code doesn't reject a mistyped value up front. The session starts, and the first request produces [There's an issue with the selected model](https://code.claude.com/docs/en/errors.md#theres-an-issue-with-the-selected-model). On the Anthropic API, a value that doesn't start with `claude-` and nearly spells a model name or alias can also produce a [startup warning that suggests it](#fix-a-mistyped-model-name).
167 172
168When the requested model has a scheduled retirement date or is automatically remapped to a newer version, Claude Code shows a warning that names the requested model. Interactive sessions show it as a startup notice. From v2.1.182, the same warning is written to stderr in [non-interactive mode](https://code.claude.com/docs/en/headless.md) when using the default text output format. The check also covers a `model` set in [subagent frontmatter](https://code.claude.com/docs/en/sub-agents.md). The stderr warning is suppressed for `--output-format json` and `stream-json`; read the actual model from the `modelUsage` field of the [result message](https://code.claude.com/docs/en/headless.md#get-structured-output) instead.173When the requested model has a scheduled retirement date or is automatically remapped to a newer version, Claude Code shows a warning that names the requested model. Interactive sessions show it as a startup notice. From v2.1.182, the same warning is written to stderr in [non-interactive mode](https://code.claude.com/docs/en/headless.md) when using the default text output format. The check also covers a `model` set in [subagent frontmatter](https://code.claude.com/docs/en/sub-agents.md). The stderr warning is suppressed for `--output-format json` and `stream-json`; read the actual model from the `modelUsage` field of the [result message](https://code.claude.com/docs/en/headless.md#get-structured-output) instead.
169 174
225 230
226## Restrict model selection231## Restrict model selection
227 232
228Administrators can use `availableModels` in [managed or policy settings](https://code.claude.com/docs/en/managed-settings.md) to restrict which models users can select. Entries match a model family such as `sonnet`, a version prefix such as `claude-sonnet-4-5`, or a full model ID such as `claude-sonnet-4-5-20250929`. A version prefix also matches later model IDs that extend it with another segment, so `claude-fable-5` permits both Fable 5 and Fable 5.1, while `claude-fable-5-1` permits Fable 5.1 only. To block a model the list permits, or to make each model ID entry permit only the version it names, see [Block specific models or versions](#block-specific-models-or-versions).233Administrators can use `availableModels` in [managed or policy settings](https://code.claude.com/docs/en/managed-settings.md) to restrict which models users can select. Each entry matches one of these:
234
235* A model family such as `sonnet`
236* A version prefix such as `claude-sonnet-4-5`. It also matches later model IDs that extend it with another segment. For example, `claude-fable-5` permits Fable 5, Fable 5.1, and Fable 5.2, while `claude-fable-5-1` permits Fable 5.1 only
237* A full model ID such as `claude-sonnet-4-5-20250929`
238
239To block a model the list permits, or to make each model ID entry permit only the version it names, see [Block specific models or versions](#block-specific-models-or-versions).
229 240
230On platforms that embed Claude Code and set [`CLAUDE_CODE_PROVIDER_MANAGED_BY_HOST`](https://code.claude.com/docs/en/env-vars), the host's model configuration takes precedence over managed model settings, while a managed `availableModels` allowlist stays in force unless the host supplies its own; [Exceptions to managed settings precedence](https://code.claude.com/docs/en/settings.md#exceptions-to-managed-settings-precedence) says which keys and variables the host overrides.241On platforms that embed Claude Code and set [`CLAUDE_CODE_PROVIDER_MANAGED_BY_HOST`](https://code.claude.com/docs/en/env-vars), the host's model configuration takes precedence over managed model settings, while a managed `availableModels` allowlist stays in force unless the host supplies its own; [Exceptions to managed settings precedence](https://code.claude.com/docs/en/settings.md#exceptions-to-managed-settings-precedence) says which keys and variables the host overrides.
231 242
465 476
466When nothing is recorded on your account, managed settings [enforce the allowlist for the Default model](#enforce-the-allowlist-for-the-default-model), and the account-type default is not in `availableModels`, `default` resolves to the enforced Default instead of the account-type default above. When an organization default and enforcement both apply, the organization default replaces the account-type default first and enforcement then applies to it: an allowlisted organization default is kept, while one outside the list resolves to the enforced Default.477When nothing is recorded on your account, managed settings [enforce the allowlist for the Default model](#enforce-the-allowlist-for-the-default-model), and the account-type default is not in `availableModels`, `default` resolves to the enforced Default instead of the account-type default above. When an organization default and enforcement both apply, the organization default replaces the account-type default first and enforcement then applies to it: an allowlisted organization default is kept, while one outside the list resolves to the enforced Default.
467 478
468Fable models are not the account-type default on any plan or provider. Choosing one with `/model` saves it as the selected model in your user settings, so later sessions start on it. For the one-time change Claude Code makes to a saved Fable 5 selection in v2.1.257, see [Work with Fable](#work-with-fable).479> [!NOTE]
480>
481> Fable models are not the account-type default on any plan or provider. Choosing one with `/model` saves it as the selected model in your user settings, so later sessions start on it, apart from the [one-time change to a saved Fable 5.1 pick](#work-with-fable).
469 482
470### `opusplan` model setting483### `opusplan` model setting
471 484
521 534
522Fable models, Opus 5.5, Sonnet 5.5, and Opus 5 run with safety classifiers, which most often flag cybersecurity and biology content. For those two categories, the fallback model depends on which model refused:535Fable models, Opus 5.5, Sonnet 5.5, and Opus 5 run with safety classifiers, which most often flag cybersecurity and biology content. For those two categories, the fallback model depends on which model refused:
523 536
524* **Fable 5.1, Fable 5, and Opus 5.5**: biology-flagged requests re-run on Opus 5, and cybersecurity-flagged requests re-run on Opus 4.8.537* **Fable models and Opus 5.5**: biology-flagged requests re-run on Opus 5, and cybersecurity-flagged requests re-run on Opus 4.8.
525* **Sonnet 5.5**: cybersecurity-flagged requests re-run on Sonnet 5. Biology-flagged requests end with a refusal instead, because Sonnet 5.5 has no biology fallback model.538* **Sonnet 5.5**: cybersecurity-flagged requests re-run on Sonnet 5. Biology-flagged requests end with a refusal instead, because Sonnet 5.5 has no biology fallback model.
526* **Opus 5**: cybersecurity-flagged requests re-run on Opus 4.8. Biology-flagged requests end with a refusal instead, because Opus 5 runs its own biology classifiers with no fallback model.539* **Opus 5**: cybersecurity-flagged requests re-run on Opus 4.8. Biology-flagged requests end with a refusal instead, because Opus 5 runs its own biology classifiers with no fallback model.
527 540
582 595
583On [Amazon Bedrock](https://code.claude.com/docs/en/amazon-bedrock.md), [Google Cloud's Agent Platform](https://code.claude.com/docs/en/google-vertex-ai.md), and [Microsoft Foundry](https://code.claude.com/docs/en/microsoft-foundry.md), model IDs are provider-specific, so automatic fallback only operates when Claude Code can identify each model involved:596On [Amazon Bedrock](https://code.claude.com/docs/en/amazon-bedrock.md), [Google Cloud's Agent Platform](https://code.claude.com/docs/en/google-vertex-ai.md), and [Microsoft Foundry](https://code.claude.com/docs/en/microsoft-foundry.md), model IDs are provider-specific, so automatic fallback only operates when Claude Code can identify each model involved:
584 597
585* Claude Code must recognize the current model as a fallback source. Fable 5.1 and Fable 5 are recognized when the model ID contains `claude-fable-5`, matches the value of `ANTHROPIC_DEFAULT_FABLE_MODEL`, or is mapped with [`modelOverrides`](#override-model-ids-per-version). Opus 5.5, Sonnet 5.5, and Opus 5 are recognized by their provider model ID or a [`modelOverrides`](#override-model-ids-per-version) mapping.598* Claude Code must recognize the current model as a fallback source. Fable models are recognized when the model ID contains `claude-fable-5`, matches the value of `ANTHROPIC_DEFAULT_FABLE_MODEL`, or is mapped with [`modelOverrides`](#override-model-ids-per-version). Opus 5.5, Sonnet 5.5, and Opus 5 are recognized by their provider model ID or a [`modelOverrides`](#override-model-ids-per-version) mapping.
586* An Opus target must resolve in your deployment, whichever model refused: set `ANTHROPIC_DEFAULT_OPUS_MODEL`, or keep an Opus 4.8 entry in the provider's model list. Without one, fallback stays off for every source model, including Sonnet 5.5, and flagged requests end with a refusal.599* An Opus target must resolve in your deployment, whichever model refused: set `ANTHROPIC_DEFAULT_OPUS_MODEL`, or keep an Opus 4.8 entry in the provider's model list. Without one, fallback stays off for every source model, including Sonnet 5.5, and flagged requests end with a refusal.
587* The flagged category's fallback model must resolve in your deployment. From a Fable model, Opus 5.5, or Opus 5, if you set `ANTHROPIC_DEFAULT_OPUS_MODEL`, flagged requests re-run on that model for every category that has a fallback; a biology flag on Opus 5 still ends with a refusal. If you don't set it, cybersecurity-flagged requests re-run on the Opus 4.8 entry, and biology-flagged requests from a Fable model or Opus 5.5 on an Opus 5 entry. From Sonnet 5.5, cybersecurity-flagged requests re-run on the model you set in `ANTHROPIC_DEFAULT_SONNET_MODEL`, or on a Sonnet 5 entry in the provider's model list if you don't set it.600* The flagged category's fallback model must resolve in your deployment. From a Fable model, Opus 5.5, or Opus 5, if you set `ANTHROPIC_DEFAULT_OPUS_MODEL`, flagged requests re-run on that model for every category that has a fallback; a biology flag on Opus 5 still ends with a refusal. If you don't set it, cybersecurity-flagged requests re-run on the Opus 4.8 entry, and biology-flagged requests from a Fable model or Opus 5.5 on an Opus 5 entry. From Sonnet 5.5, cybersecurity-flagged requests re-run on the model you set in `ANTHROPIC_DEFAULT_SONNET_MODEL`, or on a Sonnet 5 entry in the provider's model list if you don't set it.
588 601
596 609
597#### Security research and biology workloads610#### Security research and biology workloads
598 611
599Workloads in offensive security or biology, including penetration testing, Capture the Flag (CTF) exercises, and biology-adjacent codebases, trigger fallback frequently, often on the first request. For substantive biology work on Fable 5.1, Fable 5, or Opus 5.5, the first flagged request that switches models moves the session to Opus 5, and later biology-flagged requests end in refusals there, because Opus 5 has no biology fallback. On Opus 5 and Sonnet 5.5, you get those refusals from the first flagged request.612Workloads in offensive security or biology, including penetration testing, Capture the Flag (CTF) exercises, and biology-adjacent codebases, trigger fallback frequently, often on the first request. This is expected routing for these domains, not an account flag. If your organization needs Fable-class capability for this work, ask your Anthropic account team about trusted access programs.
600 613
601This is expected routing for these domains, not an account flag. If your organization needs Fable-class capability for this work, ask your Anthropic account team about trusted access programs.614For substantive biology work on a Fable model or Opus 5.5, the first flagged request that switches models moves the session to Opus 5. Later biology-flagged requests end in refusals there, because Opus 5 has no biology fallback. On Opus 5 and Sonnet 5.5, those refusals start with the first flagged request.
602 615
603### Adjust effort level616### Adjust effort level
604 617
608 621
609| Model | Levels |622| Model | Levels |
610| :- | :- |623| :- | :- |
611| Fable 5.1 and Fable 5 | `low`, `medium`, `high`, `xhigh`, `max` |624| Fable models | `low`, `medium`, `high`, `xhigh`, `max` |
612| Opus 5.5, Sonnet 5.5, Haiku 5.5, Opus 5, Sonnet 5, Opus 4.8, and Opus 4.7 | `low`, `medium`, `high`, `xhigh`, `max` |625| Opus 5.5, Sonnet 5.5, Haiku 5.5, Opus 5, Sonnet 5, Opus 4.8, and Opus 4.7 | `low`, `medium`, `high`, `xhigh`, `max` |
613| Opus 4.6 and Sonnet 4.6 | `low`, `medium`, `high`, `max` |626| Opus 4.6 and Sonnet 4.6 | `low`, `medium`, `high`, `max` |
614 627
6202. A level you pick in the session, such as with `/effort`, the `/model` picker, or [`applyFlagSettings()`](https://code.claude.com/docs/en/agent-sdk/typescript#applyflagsettings)6332. A level you pick in the session, such as with `/effort`, the `/model` picker, or [`applyFlagSettings()`](https://code.claude.com/docs/en/agent-sdk/typescript#applyflagsettings)
6213. Launching with `--effort`6343. Launching with `--effort`
6224. Your settings: the level you saved for the model or an [`effortLevel`](https://code.claude.com/docs/en/settings-reference#effortlevel) key, with the precedence between them and across settings files stated at [`modelSettings`](https://code.claude.com/docs/en/settings-reference#modelsettings)6354. Your settings: the level you saved for the model or an [`effortLevel`](https://code.claude.com/docs/en/settings-reference#effortlevel) key, with the precedence between them and across settings files stated at [`modelSettings`](https://code.claude.com/docs/en/settings-reference#modelsettings)
6235. The model's default effort: `high` on every model that supports effort, except that Opus 5.5, Sonnet 5.5, and Haiku 5.5 default to `medium` and Opus 4.7 defaults to `xhigh`. If your organization sets a default effort level for its [organization default model](#organization-default-model), that level is the default when you run that model.6365. The model's default effort: Fable 5.2, Opus 5.5, Sonnet 5.5, and Haiku 5.5 default to `medium`, and Opus 4.7 defaults to `xhigh`. Other models in the [effort levels table](#adjust-effort-level) default to `high`. If your organization sets a default effort level for its [organization default model](#organization-default-model), that level is the default when you run that model.
624 637
625After an automatic model fallback, see [Effort level after a fallback](#effort-level-after-a-fallback) for the level that applies. For subagents and teammates, see [Effort level of subagents and teammates](#effort-level-of-subagents-and-teammates).638After an automatic model fallback, see [Effort level after a fallback](#effort-level-after-a-fallback) for the level that applies. For subagents and teammates, see [Effort level of subagents and teammates](#effort-level-of-subagents-and-teammates).
626 639
671| Level | When to use it |684| Level | When to use it |
672| :- | :- |685| :- | :- |
673| `low` | Quick exchanges where you review each result, such as brainstorming, a first sketch, or a small change like a rename |686| `low` | Quick exchanges where you review each result, such as brainstorming, a first sketch, or a small change like a rename |
674| `medium` | The default on Opus 5.5, Sonnet 5.5, and Haiku 5.5. On Opus 5.5 and Sonnet 5.5, it fits day-to-day engineering work with a clear scope, such as implementing a new feature. On models with a higher default, reduces token usage for cost-sensitive work that can trade off some intelligence |687| `medium` | The default on the Fable 5.2, Opus 5.5, Sonnet 5.5, and Haiku 5.5 models. On Opus 5.5 and Sonnet 5.5, it fits day-to-day engineering work with a clear scope, such as implementing a new feature. On models with a higher default, reduces token usage for cost-sensitive work that can trade off some intelligence |
675| `high` | Work where verification matters or edge cases are likely, such as fixing a bug in an existing codebase. The default on every model except Opus 5.5, Sonnet 5.5, Haiku 5.5, and Opus 4.7 |688| `high` | Work where verification matters or edge cases are likely, such as fixing a bug in an existing codebase. The default on the other models in the effort table |
676| `xhigh` | Deeper reasoning at higher token spend. The default on Opus 4.7 |689| `xhigh` | Deeper reasoning at higher token spend. The default on Opus 4.7 |
677| `max` | Hard problems you want Claude to work through without you, such as finding security vulnerabilities. `max` may show diminishing returns and is prone to overthinking, so test before adopting it broadly |690| `max` | Hard problems you want Claude to work through without you, such as finding security vulnerabilities. `max` may show diminishing returns and is prone to overthinking, so test before adopting it broadly |
678| `ultracode` | A Claude Code setting rather than a level: plans a [dynamic workflow](https://code.claude.com/docs/en/workflows.md) for each substantive task at any effort level |691| `ultracode` | A Claude Code setting rather than a level: plans a [dynamic workflow](https://code.claude.com/docs/en/workflows.md) for each substantive task at any effort level |
691 704
692* Retype it outside anything such as quotes, brackets, a path, or a command, in a prompt that doesn't start with `/`705* Retype it outside anything such as quotes, brackets, a path, or a command, in a prompt that doesn't start with `/`
693* Unset `CLAUDE_CODE_EFFORT_LEVEL` if it's set below `xhigh`, raise your own [`maxEffortLevel`](https://code.claude.com/docs/en/settings-reference#maxeffortlevel) to `xhigh` or above, or ask an organization admin to raise your [organization's limit](#organization-effort-limits)706* Unset `CLAUDE_CODE_EFFORT_LEVEL` if it's set below `xhigh`, raise your own [`maxEffortLevel`](https://code.claude.com/docs/en/settings-reference#maxeffortlevel) to `xhigh` or above, or ask an organization admin to raise your [organization's limit](#organization-effort-limits)
694* Run `/model` in your session to switch to an Opus 5.5, Sonnet 5.5, Haiku 5.5, or Fable 5.1 model. Where the word can't raise a turn, such as on Amazon Bedrock, [set the effort level](#set-the-effort-level) instead707* Run `/model` in your session to switch to an Opus 5.5, Sonnet 5.5, Haiku 5.5, Fable 5.2, or Fable 5.1 model. Where the word can't raise a turn, such as on Amazon Bedrock, [set the effort level](#set-the-effort-level) instead
695 708
696#### Set the effort level709#### Set the effort level
697 710
767 780
768### Extended context781### Extended context
769 782
770Fable 5.1, Fable 5, Sonnet 5 and later, Haiku 5.5, Opus 4.6 and later, and Sonnet 4.6 support a [1 million token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows#context-window-sizes-by-model) for long sessions with large codebases.783Long sessions with large codebases can use a [1 million token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows#context-window-sizes-by-model). Fable models, Sonnet 5 and later, Haiku 5.5, Opus 4.6 and later, and Sonnet 4.6 support it.
771 784
772Fable 5.1, Fable 5, Sonnet 5 and later, Haiku 5.5, and Opus 4.7 and later run with the 1M window by default, with no `[1m]` suffix needed. That includes sessions on Amazon Bedrock, Google Cloud's Agent Platform, and Microsoft Foundry, and [Claude apps gateway](https://code.claude.com/docs/en/claude-apps-gateway) sessions. To run them with a 200K window instead, see [Turn off 1M context](#turn-off-1m-context).785Fable models, Sonnet 5 and later, Haiku 5.5, and Opus 4.7 and later run with the 1M window by default, with no `[1m]` suffix needed. That includes sessions on Amazon Bedrock, Google Cloud's Agent Platform, and Microsoft Foundry, and [Claude apps gateway](https://code.claude.com/docs/en/claude-apps-gateway) sessions. To run them with a 200K window instead, see [Turn off 1M context](#turn-off-1m-context).
773 786
774Opus 4.6 and Sonnet 4.6 reach 1M only through their `[1m]` variant, and access to that variant depends on your plan. On Max, Ultra, Team, and Enterprise plans, including both Team Standard and Team Premium seats, Opus 4.6 with 1M context is included with your subscription. Sonnet 4.6 with 1M context requires [usage credits](https://support.claude.com/en/articles/12429409-extra-usage-for-paid-claude-plans) on every subscription plan, including Max and Ultra.787Opus 4.6 and Sonnet 4.6 reach 1M only through their `[1m]` variant, and access to that variant depends on your plan. On Max, Ultra, Team, and Enterprise plans, including both Team Standard and Team Premium seats, Opus 4.6 with 1M context is included with your subscription. Sonnet 4.6 with 1M context requires [usage credits](https://support.claude.com/en/articles/12429409-extra-usage-for-paid-claude-plans) on every subscription plan, including Max and Ultra.
775 788
798 811
799#### Context window behind an LLM gateway812#### Context window behind an LLM gateway
800 813
801If you set `ANTHROPIC_BASE_URL` to an [LLM gateway](https://code.claude.com/docs/en/llm-gateway) or another proxy, Claude Code gives each model it recognizes the same context window the model has on the Anthropic API. Fable 5.1, Fable 5, Sonnet 5 and later, Haiku 5.5, and Opus 4.7 and later get the 1M window with no `[1m]` variant to select, and a model that reaches 1M only through its `[1m]` variant, such as Opus 4.6, runs at 200K without it. Claude Code can't detect a lower limit that the gateway or the server behind it enforces. If your gateway rejects requests above 200K tokens, set [`CLAUDE_CODE_AUTO_COMPACT_WINDOW=200000`](https://code.claude.com/docs/en/env-vars) in the environment that starts Claude Code, so sessions on every model [compact at that boundary](#set-the-auto-compact-window).814If you set `ANTHROPIC_BASE_URL` to an [LLM gateway](https://code.claude.com/docs/en/llm-gateway) or another proxy, Claude Code gives each model it recognizes the same context window the model has on the Anthropic API. Fable models, Sonnet 5 and later, Haiku 5.5, and Opus 4.7 and later get the 1M window with no `[1m]` variant. A model that reaches 1M only through its `[1m]` variant, such as Opus 4.6, runs at 200K without it.
815
816Claude Code can't detect a lower limit that the gateway or the server behind it enforces. If your gateway rejects requests above 200K tokens, set [`CLAUDE_CODE_AUTO_COMPACT_WINDOW=200000`](https://code.claude.com/docs/en/env-vars) in the environment that starts Claude Code, so sessions on every model [compact at that boundary](#set-the-auto-compact-window).
802 817
803#### Turn off 1M context818#### Turn off 1M context
804 819
885 900
886Once Claude Code recognizes the ID or uses the window you gave it, the warning no longer appears when you start a session on that ID.901Once Claude Code recognizes the ID or uses the window you gave it, the warning no longer appears when you start a session on that ID.
887 902
903#### Fix a mistyped model name
904
905Either of these warnings means Claude Code doesn't recognize the model ID you set, and the ID nearly spells a model name or alias it does recognize:
906
907```text theme={null}
908⚠ Model "<model>" isn't recognized · did you mean "<suggestion>"?
909Claude Code doesn't recognize the model "<model>". Did you mean "<suggestion>"?
910```
911
912* **You mistyped the ID**: change it to the suggestion [wherever you set the model](#setting-your-model)
913* **The ID is deliberate**: leave it as it is. The session sends it as you wrote it. If the context window Claude Code assumes for it is wrong, [correct the window](#correct-the-window-for-a-gateway-or-custom-model-id)
914
888#### Which IDs `CLAUDE_CODE_MAX_CONTEXT_TOKENS` applies to915#### Which IDs `CLAUDE_CODE_MAX_CONTEXT_TOKENS` applies to
889 916
890On an [LLM gateway](https://code.claude.com/docs/en/llm-gateway) or other custom deployment, Claude Code can assume a context window for the model ID that differs from the model's real window, whether or not it resolves the ID to a Claude model. Set [`CLAUDE_CODE_MAX_CONTEXT_TOKENS`](https://code.claude.com/docs/en/env-vars) to the window Claude Code should assume instead.917On an [LLM gateway](https://code.claude.com/docs/en/llm-gateway) or other custom deployment, Claude Code can assume a context window for the model ID that differs from the model's real window, whether or not it resolves the ID to a Claude model. Set [`CLAUDE_CODE_MAX_CONTEXT_TOKENS`](https://code.claude.com/docs/en/env-vars) to the window Claude Code should assume instead.
1100 1127
1101| Version | Change |1128| Version | Change |
1102| :- | :- |1129| :- | :- |
1130| v2.1.321 | `fable` resolves to Fable 5.2, except in Claude apps gateway sessions |
1131| v2.1.321 | `best` resolves to the same model as `opus`. Earlier versions use the model `fable` resolves to, where Fable is available |
1103| v2.1.293 | `haiku` resolves to Haiku 5.5 on the Anthropic API |1132| v2.1.293 | `haiku` resolves to Haiku 5.5 on the Anthropic API |
1104| v2.1.284 | `sonnet` resolves to Sonnet 5.5 on the Anthropic API |1133| v2.1.284 | `sonnet` resolves to Sonnet 5.5 on the Anthropic API |
1105| v2.1.280 | `opus` resolves to Opus 5.5 on the Anthropic API, Claude Platform on AWS, Amazon Bedrock, and Google Cloud's Agent Platform |1134| v2.1.280 | `opus` resolves to Opus 5.5 on the Anthropic API, Claude Platform on AWS, Amazon Bedrock, and Google Cloud's Agent Platform |
