An entry is only as true as the day it was written.
Flags move on the server after a release ships. Anthropic's own notes land days later and their documentation later still. Sometimes an entry turns out to be wrong and gets corrected by hand. All of that is recorded against the entry it happened to, and this is the whole of it in the order it happened.
Nothing here replaces an entry. Every line links to the page its release published, still saying what that release said, because a correction is added and dated rather than swapped in.
| When | Entry | What happened |
|---|---|---|
v2.1.239tengu_toasty_breeze |
Flag reading movedThe flag server now returns {"enabled":false,"version":0} for tengu_toasty_breeze, read as this account. | |
v2.1.248tengu_nifty_lemur |
Flag reading movedThe flag server now returns {"enabled":false,"version":0} for tengu_nifty_lemur, read as this account. | |
v2.1.248tengu_nifty_lemur |
Flag reading movedThe flag server now returns {"enabled":false,"version":0} for tengu_nifty_lemur, read as this account. | |
v2.1.251tengu_juniper_relay |
Flag reading movedThe flag server now returns off for tengu_juniper_relay, read as this account. | |
v2.1.223tengu_juniper_relay |
Flag reading movedThe flag server now returns off for tengu_juniper_relay, read as this account. | |
v2.1.280/fast |
Documentation arrivedAnthropic's documentation has since written up /fast, on overview.
the line in the docs* [Fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) (research preview) is available for Claude Opus 5.5 on the Claude API. |
|
v2.1.280prefix_mismatch_behavior |
Documentation arrivedAnthropic's documentation has since written up prefix_mismatch_behavior, on Or, for the Project Glasswing model with the same capabilities:.
the line in the docsprefix_mismatch_behavior: drop_block |
|
v2.1.280/config |
Documentation arrivedAnthropic's documentation has since written up /config, on files.
the line in the docsmount_path: /config.json |
|
v2.1.280claude-opus-5-5 |
Documentation arrivedA small documentation edit on API usage primer for Claude touched a line naming claude-opus-5-5 after this was published.
the line in the docs* Claude Opus 5.5 (`claude-opus-5-5`, adaptive thinking only, always on) |
|
v2.1.280claude-opus-5-5 |
Documentation arrivedA small documentation edit on API usage primer for Claude touched a line naming claude-opus-5-5 after this was published.
the line in the docs* Claude Opus 5.5 (`claude-opus-5-5`, adaptive thinking only, always on) |
|
v2.1.280claude-opus-5-5 |
Documentation arrivedA small documentation edit on API usage primer for Claude touched a line naming claude-opus-5-5 after this was published.
the line in the docs* Claude Opus 5.5 (`claude-opus-5-5`, adaptive thinking only, always on) |
|
v2.1.280claude-opus-5-5 |
Documentation arrivedA small documentation edit on API usage primer for Claude touched a line naming claude-opus-5-5 after this was published.
the line in the docs* Claude Opus 5.5 (`claude-opus-5-5`, adaptive thinking only, always on) |
|
v2.1.280/effort |
Documentation arrivedAnthropic's documentation has since written up /effort, on prompting-claude-opus-5.
the line in the docsClaude Opus 5 runs with [thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) on by default, and thinking can be disabled only at [effort](https://platform.claude.com/docs/en/build-with-claude/effort) `high` or below. … |
|
v2.1.280/effort |
Documentation arrivedAnthropic's documentation has since written up /effort, on prompting-claude-opus-5.
the line in the docsClaude Opus 5 runs with [thinking](https://platform.claude.com/docs/en/build-with-claude/thinking) on by default, and thinking can be disabled only at [effort](https://platform.claude.com/docs/en/build-with-claude/effort) `high` or below. … |
|
v2.1.248claude-opus-4-8 |
Documentation arrivedA small documentation edit on prompting-claude-opus-4-8 touched a line naming claude-opus-4-8 after this was published.
the line in the docsThis guide covers the prompting patterns specific to Claude Opus 4.8. For the API changes involved in moving from Claude Opus 4.8 to Claude Opus 5.5, see [Migrating to Claude Opus 5.5 from Claude Opus 4.8](https://platform.claude.com/docs/… |
|
v2.1.280opus-4-8 |
Documentation arrivedA small documentation edit on prompting-claude-opus-4-8 touched a line naming opus-4-8 after this was published.
the line in the docsThis guide covers the prompting patterns specific to Claude Opus 4.8. For the API changes involved in moving from Claude Opus 4.8 to Claude Opus 5.5, see [Migrating to Claude Opus 5.5 from Claude Opus 4.8](https://platform.claude.com/docs/… |
|
v2.1.246opus-4-8 |
Documentation arrivedA small documentation edit on prompting-claude-opus-4-8 touched a line naming opus-4-8 after this was published.
the line in the docsThis guide covers the prompting patterns specific to Claude Opus 4.8. For the API changes involved in moving from Claude Opus 4.8 to Claude Opus 5.5, see [Migrating to Claude Opus 5.5 from Claude Opus 4.8](https://platform.claude.com/docs/… |
|
v2.1.280system |
Documentation arrivedA small documentation edit on Delivering work touched a line naming system after this was published.
the line in the docsClaude Fable 5.1's writing has few stock phrases and little unexplained jargon. In some cases, though, its prose is denser than Claude Fable 5's: sentences run longer and there are fewer paragraph breaks. An instruction that defines the an… |
|
v2.1.280user |
Documentation arrivedA small documentation edit on Delivering work touched a line naming user after this was published.
the line in the docsClaude Fable 5.1's writing has few stock phrases and little unexplained jargon. In some cases, though, its prose is denser than Claude Fable 5's: sentences run longer and there are fewer paragraph breaks. An instruction that defines the an… |
|
v2.1.280max |
Documentation arrivedA small documentation edit on Request 2 caches its request content (not the response) touched a line naming max after this was published.
the line in the docsecho $prewarm->stopReason, PHP_EOL; // "max_tokens" |
|
v2.1.274position |
Documentation arrivedA small documentation edit on Request 2 caches its request content (not the response) touched a line naming position after this was published.
the line in the docs| **Dropped thinking blocks** | ✓ | ✓ | ✘ | When the API drops a Claude Fable 5.1, Claude Mythos 5.1, or Claude Opus 5.5 thinking block that isn't [preserved](https://platform.claude.com/docs/en/build-with-claude/thinking#preserved-thinkin… |
|
v2.1.280opus-4-6 |
Documentation arrivedA small documentation edit on fast-mode touched a line naming opus-4-6 after this was published.
the line in the docsFast mode is not available on Claude Opus 4.6. Requests to `claude-opus-4-6` with `speed: "fast"` do not return an error: they run at standard speed and are billed at [standard rates](https://platform.claude.com/docs/en/about-claude/pricin… |
|
v2.1.280check |
Documentation arrivedA small documentation edit on fast-mode touched a line naming check after this was published.
the line in the docsFast mode is not available on Claude Opus 4.6. Requests to `claude-opus-4-6` with `speed: "fast"` do not return an error: they run at standard speed and are billed at [standard rates](https://platform.claude.com/docs/en/about-claude/pricin… |
|
v2.1.268claude-opus-4-6 |
Documentation arrivedA small documentation edit on fast-mode touched a line naming claude-opus-4-6 after this was published.
the line in the docsFast mode is not available on Claude Opus 4.6. Requests to `claude-opus-4-6` with `speed: "fast"` do not return an error: they run at standard speed and are billed at [standard rates](https://platform.claude.com/docs/en/about-claude/pricin… |
|
v2.1.280/fast |
Documentation arrivedA small documentation edit on fast-mode touched a line naming /fast after this was published.
the line in the docsFast mode is not available on Claude Opus 4.6. Requests to `claude-opus-4-6` with `speed: "fast"` do not return an error: they run at standard speed and are billed at [standard rates](https://platform.claude.com/docs/en/about-claude/pricin… |
|
v2.1.280opus-4-7 |
Documentation arrivedA small documentation edit on fast-mode touched a line naming opus-4-7 after this was published.
the line in the docsFast mode is not available on Claude Opus 4.7. Requests to `claude-opus-4-7` with `speed: "fast"` return an error; unlike Claude Opus 4.6 (see the following note), requests do not fall back to standard speed. The model itself remains avail… |
|
v2.1.268claude-opus-4-7 |
Documentation arrivedA small documentation edit on fast-mode touched a line naming claude-opus-4-7 after this was published.
the line in the docsFast mode is not available on Claude Opus 4.7. Requests to `claude-opus-4-7` with `speed: "fast"` return an error; unlike Claude Opus 4.6 (see the following note), requests do not fall back to standard speed. The model itself remains avail… |
|
v2.1.248claude-opus-4-7 |
Documentation arrivedA small documentation edit on fast-mode touched a line naming claude-opus-4-7 after this was published.
the line in the docsFast mode is not available on Claude Opus 4.7. Requests to `claude-opus-4-7` with `speed: "fast"` return an error; unlike Claude Opus 4.6 (see the following note), requests do not fall back to standard speed. The model itself remains avail… |
|
v2.1.280trigger |
Documentation arrivedAnthropic's documentation has since written up trigger, on context-editing.
the line in the docstrigger: |
|
v2.1.257mythos-5-1 |
Documentation arrivedA small documentation edit on claude-on-vertex-ai touched a line naming mythos-5-1 after this was published.
the line in the docs| Claude Mythos 5.1 ([limited availability](https://anthropic.com/glasswing)) | `claude-mythos-5-1` | |
|
v2.1.257claude-mythos-5-1 |
Documentation arrivedA small documentation edit on claude-on-vertex-ai touched a line naming claude-mythos-5-1 after this was published.
the line in the docs| Claude Mythos 5.1 ([limited availability](https://anthropic.com/glasswing)) | `claude-mythos-5-1` | |
|
v2.1.257claude-mythos-5-1 |
Documentation arrivedA small documentation edit on claude-on-vertex-ai touched a line naming claude-mythos-5-1 after this was published.
the line in the docs| Claude Mythos 5.1 ([limited availability](https://anthropic.com/glasswing)) | `claude-mythos-5-1` | |
|
v2.1.280/model |
Documentation arrivedA small documentation edit on Message Batches API touched a line naming /model after this was published.
the line in the docs* **Retired:** May still be available on other cloud platforms. See [Model deprecations](https://platform.claude.com/docs/en/about-claude/model-deprecations) for more. |
|
v2.1.280/model |
Documentation arrivedA small documentation edit on Message Batches API touched a line naming /model after this was published.
the line in the docs* **Retired:** May still be available on other cloud platforms. See [Model deprecations](https://platform.claude.com/docs/en/about-claude/model-deprecations) for more. |
|
v2.1.280/model |
Documentation arrivedA small documentation edit on Message Batches API touched a line naming /model after this was published.
the line in the docs* **Retired:** May still be available on other cloud platforms. See [Model deprecations](https://platform.claude.com/docs/en/about-claude/model-deprecations) for more. |
|
v2.1.277is_active |
Documentation arrivedAnthropic's documentation has since written up is_active, on Compliance API.
the line in the docs- `is_active: optional boolean or null` |
|
v2.1.257Retry-After |
Documentation arrivedAnthropic's documentation has since written up Retry-After, on routines-fire.
the line in the docs| 429 | `rate_limit_error` | An hourly fire limit for the routine or the account has been reached. The response includes a `Retry-After` header indicating when the window resets. | |
|
v2.1.280output_config.effort |
Documentation arrivedAnthropic's documentation has since written up output_config.effort, on Events.
the line in the docsHow hard Claude works on each turn. Sets `output_config.effort` on every Messages call the session makes. |
|
v2.1.280End |
Documentation arrivedAnthropic's documentation has since written up End, on Events.
the line in the docs- `stop_reason: BetaManagedAgentsSessionEndTurn or BetaManagedAgentsSessionRequiresAction or BetaManagedAgentsSessionRetriesExhausted or BetaManagedAgentsSessionBudgetReached` |
|
v2.1.280End |
Documentation arrivedAnthropic's documentation has since written up End, on Events.
the line in the docs- `stop_reason: BetaManagedAgentsSessionEndTurn or BetaManagedAgentsSessionRequiresAction or BetaManagedAgentsSessionRetriesExhausted or BetaManagedAgentsSessionBudgetReached` |
|
v2.1.280End |
Documentation arrivedAnthropic's documentation has since written up End, on Events.
the line in the docs- `stop_reason: BetaManagedAgentsSessionEndTurn or BetaManagedAgentsSessionRequiresAction or BetaManagedAgentsSessionRetriesExhausted or BetaManagedAgentsSessionBudgetReached` |
|
v2.1.280sonnet-4-6 |
Documentation arrivedAnthropic's documentation has since written up sonnet-4-6, on Create a Message Batch.
the line in the docs- `"claude-sonnet-4-6"` |
|
v2.1.280opus-4-6 |
Documentation arrivedAnthropic's documentation has since written up opus-4-6, on Create a Message Batch.
the line in the docs- `"claude-opus-4-6"` |
|
v2.1.280opus-4-7 |
Documentation arrivedAnthropic's documentation has since written up opus-4-7, on Create a Message Batch.
the line in the docs- `"claude-opus-4-7"` |
|
v2.1.280Tab |
Documentation arrivedAnthropic's documentation has since written up Tab, on Create a Message Batch.
the line in the docs- `close_tab: optional BetaBrowserCloseTabConfig or null` |
|
v2.1.280max |
Documentation arrivedAnthropic's documentation has since written up max, on Create a Message Batch.
the line in the docsmaxLength: 128, minLength: 1, pattern: ^[a-zA-Z0-9_-]{1,128}$ |
|
v2.1.280opus-4-8 |
Documentation arrivedAnthropic's documentation has since written up opus-4-8, on claude-api-skill.
the line in the docsFor the full list of model-specific changes the skill applies, see [Migrating to Claude Opus 5.5 from Claude Opus 5](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#migrating-from-claude-opus-5), [Migrating to Claude Op… |
|
v2.1.280claude-opus-5-5 |
Documentation arrivedAnthropic's documentation has since written up claude-opus-5-5, on claude-api-skill.
the line in the docsWhen the scope is ambiguous (for example, a bare `/claude-api migrate to claude-opus-5-5`), the skill asks you to choose between the entire working directory, a specific subdirectory, or an explicit file list before editing any files. This… |
|
v2.1.280claude-opus-5-5 |
Documentation arrivedAnthropic's documentation has since written up claude-opus-5-5, on claude-api-skill.
the line in the docsWhen the scope is ambiguous (for example, a bare `/claude-api migrate to claude-opus-5-5`), the skill asks you to choose between the entire working directory, a specific subdirectory, or an explicit file list before editing any files. This… |
|
v2.1.280claude-opus-5-5 |
Documentation arrivedAnthropic's documentation has since written up claude-opus-5-5, on claude-api-skill.
the line in the docsWhen the scope is ambiguous (for example, a bare `/claude-api migrate to claude-opus-5-5`), the skill asks you to choose between the entire working directory, a specific subdirectory, or an explicit file list before editing any files. This… |