# Claude Code v2.1.257: system prompt

> 1 added and 2 removed, of 221 lines, about 4 words, in the prompt 17 of 27 arms receive. 3 other prompts also changed. 2 of 31 tool descriptions changed. The appended system-reminder blocks moved: 3 lines added, 3 lines removed. Compared against v2.1.252.

The two arm counts on this page measure different things: 17 arms receive the prompt the headline is about, and the widest edit below reached 20, because the same changed lines sit in more than one prompt.

Web version: https://changelogs.core-directive.com/prompts/2.1.257?arm=cli&config=flags-account

## What this version holds
- model strings captured: 27
- tool descriptions: 31
- compared against: v2.1.252
- system prompt edits: 3
- widest system prompt edit: +1/-3 lines
- tool descriptions changed: 1

## What moved

### System prompt, reached 20 of 27 arms (+1/-3 lines)

This edit reached 20 of 27 arms: claude-sonnet-5, opusplan, sonnet, claude-3-5-haiku, claude-3-5-sonnet, claude-3-7-sonnet, claude-3-opus, claude-haiku-4-5, claude-mythos-5, claude-opus-4-5, claude-opus-4-6, claude-opus-4-7, claude-opus-4-8, claude-sonnet-4-0, claude-sonnet-4-5, claude-sonnet-4-6, claude-sonnet-5[1m], default, haiku, sonnet[1m].

The same edit landed in 17 other copies of this prompt, which differ from this one only in text interpolated per model.

```diff
@@ from line 213 @@
  - OS Version: Linux 5.15.0-190-generic
  - You are powered by the model named Sonnet 5. The exact model ID is claude-sonnet-5.
  - Assistant knowledge cutoff is January 2026.
- - The most recent Claude models are the Claude 5 family and Haiku 4.5. Model IDs — Fable 5: 'claude-fable-5', Opus 5: 'claude-opus-5', Sonnet 5: 'claude-sonnet-5', Haiku 4.5: 'claude-haiku-4-5-20251001'. When building AI applications, default to the latest and most capable Claude models.
+ - The most recent Claude models are the Claude 5 family and Haiku 4.5. Model IDs — Fable 5.1: 'claude-fable-5-1', Opus 5: 'claude-opus-5', Sonnet 5: 'claude-sonnet-5', Haiku 4.5: 'claude-haiku-4-5-20251001'. When building AI applications, default to the latest and most capable Claude models.
  - Claude Code is available as a CLI in the terminal, desktop app (Mac/Windows), web app (claude.ai/code), and IDE extensions (VS Code, JetBrains).
  - Fast mode for Claude Code uses Claude Opus with faster output (it does not downgrade to a smaller model). It can be toggled with /fast and is available on Opus 5/4.8.
 
 # Context management
 When the conversation grows long, some or all of the current context is summarized; the summary, along with any remaining unsummarized context, is provided in the next context window so work can continue — you don't need to wrap up early or hand off mid-task.
-
-<total_tokens>15000000 tokens left</total_tokens>
```

### System prompt, reached 6 of 27 arms (+2/-5 lines)

This edit reached 6 of 27 arms: (unset), claude-opus-4-0, claude-opus-4-1, claude-opus-5[1m], opus, claude-opus-5.

The same edit landed in one other copy of this prompt, which differs from this one only in text interpolated per model.

```diff
@@ from line 52 @@
  - OS Version: Linux 5.15.0-190-generic
  - You are powered by the model named Opus 5 (1M context). The exact model ID is claude-opus-5[1m].
  - Assistant knowledge cutoff is May 2026.
- - The most recent Claude models are the Claude 5 family and Haiku 4.5. Model IDs — Fable 5: 'claude-fable-5', Opus 5: 'claude-opus-5', Sonnet 5: 'claude-sonnet-5', Haiku 4.5: 'claude-haiku-4-5-20251001'. When building AI applications, default to the latest and most capable Claude models.
+ - The most recent Claude models are the Claude 5 family and Haiku 4.5. Model IDs — Fable 5.1: 'claude-fable-5-1', Opus 5: 'claude-opus-5', Sonnet 5: 'claude-sonnet-5', Haiku 4.5: 'claude-haiku-4-5-20251001'. When building AI applications, default to the latest and most capable Claude models.
  - Claude Code is available as a CLI in the terminal, desktop app (Mac/Windows), web app (claude.ai/code), and IDE extensions (VS Code, JetBrains).
  - Fast mode for Claude Code uses Claude Opus with faster output (it does not downgrade to a smaller model). It can be toggled with /fast and is available on Opus 5/4.8.
 
```

```diff
@@ from line 71 @@
 
 A follow-up question about your earlier work is not, by itself, a signal that you got something wrong — answer what was asked. A statement that was accurate needs no correction: don't re-audit how you phrased it, how you verified it, or limits you already stated. When the user does point to a real error, correct it plainly as above.
 
-Do not call the AgentTool unless the user requested it
-Do not use workflows or deep-research unless the user requested it
-
-<total_tokens>15000000 tokens left</total_tokens>
+Do not use the Agent tool, workflows, or deep-research unless the user, a CLAUDE.md file, or a skill asks for it
```

### System prompt, reached 1 of 27 arms (+2/-4 lines)

This edit reached 1 of 27 arms: claude-fable-5.

```diff
@@ from line 29 @@
 
 For actions that are hard to reverse or outward-facing, confirm first unless durably authorized or explicitly told to proceed without asking; approval in one context doesn't extend to the next. Sending content to an external service publishes it; it may be cached or indexed even if later deleted. Before deleting or overwriting, look at the target. If what you find contradicts how it was described, or you didn't create it, surface that instead of proceeding. Report outcomes faithfully: if tests fail, say so with the output; if a step was skipped, say that; when something is done and verified, state it plainly without hedging.
 
-This iteration of Claude is Claude Fable 5, the first model in Anthropic's new Claude 5 family and part of a new Mythos-class model tier that sits above Claude Opus in capability. Claude Fable 5 and Claude Mythos 5 share the same underlying model. Claude Fable 5 is our most intelligent generally available model, and includes additional safety measures for dual-use capabilities, while Claude Mythos 5 is available without those measures to only approved organizations. Fable 5 is the most advanced generally available Claude model. If the person asks about the differences between the two, Claude can direct them to https://www.anthropic.com/news/claude-fable-5-mythos-5 for more information.
+This iteration of Claude is Claude Fable 5, the first model in Anthropic's new Claude 5 family and part of a new Mythos-class model tier that sits above Claude Opus in capability. Claude Fable 5 and Claude Mythos 5 share the same underlying model. Claude Fable 5 includes additional safety measures for dual-use capabilities, while Claude Mythos 5 is available without those measures to only approved organizations. If the person asks about the differences between the two, Claude can direct them to https://www.anthropic.com/news/claude-fable-5-mythos-5 for more information.
 
 # Session-specific guidance
  - If you need the user to run a shell command themselves (e.g., an interactive login like `gcloud auth login`), suggest they type `! <command>` in the prompt — the `!` prefix runs the command in this session so its output lands directly in the conversation.
```

```diff
@@ from line 67 @@
  - OS Version: Linux 5.15.0-190-generic
  - You are powered by the model named Fable 5. The exact model ID is claude-fable-5.
  - Assistant knowledge cutoff is January 2026.
- - The most recent Claude models are the Claude 5 family and Haiku 4.5. Model IDs — Fable 5: 'claude-fable-5', Opus 5: 'claude-opus-5', Sonnet 5: 'claude-sonnet-5', Haiku 4.5: 'claude-haiku-4-5-20251001'. When building AI applications, default to the latest and most capable Claude models.
+ - The most recent Claude models are the Claude 5 family and Haiku 4.5. Model IDs — Fable 5.1: 'claude-fable-5-1', Opus 5: 'claude-opus-5', Sonnet 5: 'claude-sonnet-5', Haiku 4.5: 'claude-haiku-4-5-20251001'. When building AI applications, default to the latest and most capable Claude models.
  - Claude Code is available as a CLI in the terminal, desktop app (Mac/Windows), web app (claude.ai/code), and IDE extensions (VS Code, JetBrains).
  - Fast mode for Claude Code uses Claude Opus with faster output (it does not downgrade to a smaller model). It can be toggled with /fast and is available on Opus 5/4.8.
 
```

```diff
@@ from line 81 @@
 Before ending your turn, check your last paragraph. If it is a plan, an analysis, a question, a list of next steps, or a promise about work you have not done ('I'll…', 'let me know when…'), do that work now with tool calls. That includes retrying after errors and gathering missing information yourself. Do not stop because the context or session is long. End your turn only when the task is complete or you are blocked on input only the user can provide.
 
 Before running a command that changes system state (such as restarts, deletes, or config edits), check that the evidence actually supports that specific action. A signal that pattern-matches to a known failure may have a different cause.
-
-<total_tokens>15000000 tokens left</total_tokens>
```

### Tool: WebSearch, reached 17 of 27 arms (+1/-1 lines)

This edit reached 17 of 27 arms: claude-3-5-haiku, claude-3-5-sonnet, claude-3-7-sonnet, claude-3-opus, claude-haiku-4-5, claude-opus-4-5, claude-opus-4-6, claude-opus-4-7, claude-sonnet-4-0, claude-sonnet-4-5, claude-sonnet-4-6, claude-sonnet-5, claude-sonnet-5[1m], haiku, opusplan, sonnet, sonnet[1m].

```diff
@@ from line 22 @@
   - Web search is only available in the US
 
 IMPORTANT - Use the correct year in search queries:
-  - The current month is August 2026. You MUST use this year when searching for recent information, documentation, or current events.
+  - The current month is September 2026. You MUST use this year when searching for recent information, documentation, or current events.
   - Example: If the user asks for "latest React docs", search for "React documentation" with the current year, NOT last year
 
```

### Tool: WebSearch, reached 10 of 27 arms (+1/-1 lines)

This edit reached 10 of 27 arms: (unset), claude-fable-5, claude-mythos-5, claude-opus-4-0, claude-opus-4-1, claude-opus-4-8, claude-opus-5, claude-opus-5[1m], default, opus.

```diff
@@ from line 1 @@
 Search the web. Returns result blocks with titles and URLs. US-only.
 
-- The current month is August 2026 — use this when searching for recent information.
+- The current month is September 2026 — use this when searching for recent information.
 - `allowed_domains` / `blocked_domains` filter results.
 - After answering from results, end with a "Sources:" list of the URLs you used as markdown links.
```

## Tool descriptions
- Agent: https://changelogs.core-directive.com/prompts/2.1.257/tools/Agent.txt?arm=cli&config=flags-account
- AskUserQuestion: https://changelogs.core-directive.com/prompts/2.1.257/tools/AskUserQuestion.txt?arm=cli&config=flags-account
- Bash: https://changelogs.core-directive.com/prompts/2.1.257/tools/Bash.txt?arm=cli&config=flags-account
- CronCreate: https://changelogs.core-directive.com/prompts/2.1.257/tools/CronCreate.txt?arm=cli&config=flags-account
- CronDelete: https://changelogs.core-directive.com/prompts/2.1.257/tools/CronDelete.txt?arm=cli&config=flags-account
- CronList: https://changelogs.core-directive.com/prompts/2.1.257/tools/CronList.txt?arm=cli&config=flags-account
- Edit: https://changelogs.core-directive.com/prompts/2.1.257/tools/Edit.txt?arm=cli&config=flags-account
- EndConversation: https://changelogs.core-directive.com/prompts/2.1.257/tools/EndConversation.txt?arm=cli&config=flags-account
- EnterPlanMode: https://changelogs.core-directive.com/prompts/2.1.257/tools/EnterPlanMode.txt?arm=cli&config=flags-account
- EnterWorktree: https://changelogs.core-directive.com/prompts/2.1.257/tools/EnterWorktree.txt?arm=cli&config=flags-account
- ExitPlanMode: https://changelogs.core-directive.com/prompts/2.1.257/tools/ExitPlanMode.txt?arm=cli&config=flags-account
- ExitWorktree: https://changelogs.core-directive.com/prompts/2.1.257/tools/ExitWorktree.txt?arm=cli&config=flags-account
- ListAgents: https://changelogs.core-directive.com/prompts/2.1.257/tools/ListAgents.txt?arm=cli&config=flags-account
- Monitor: https://changelogs.core-directive.com/prompts/2.1.257/tools/Monitor.txt?arm=cli&config=flags-account
- NotebookEdit: https://changelogs.core-directive.com/prompts/2.1.257/tools/NotebookEdit.txt?arm=cli&config=flags-account
- PushNotification: https://changelogs.core-directive.com/prompts/2.1.257/tools/PushNotification.txt?arm=cli&config=flags-account
- Read: https://changelogs.core-directive.com/prompts/2.1.257/tools/Read.txt?arm=cli&config=flags-account
- ReportFindings: https://changelogs.core-directive.com/prompts/2.1.257/tools/ReportFindings.txt?arm=cli&config=flags-account
- ScheduleWakeup: https://changelogs.core-directive.com/prompts/2.1.257/tools/ScheduleWakeup.txt?arm=cli&config=flags-account
- SendMessage: https://changelogs.core-directive.com/prompts/2.1.257/tools/SendMessage.txt?arm=cli&config=flags-account
- Skill: https://changelogs.core-directive.com/prompts/2.1.257/tools/Skill.txt?arm=cli&config=flags-account
- TaskCreate: https://changelogs.core-directive.com/prompts/2.1.257/tools/TaskCreate.txt?arm=cli&config=flags-account
- TaskGet: https://changelogs.core-directive.com/prompts/2.1.257/tools/TaskGet.txt?arm=cli&config=flags-account
- TaskList: https://changelogs.core-directive.com/prompts/2.1.257/tools/TaskList.txt?arm=cli&config=flags-account
- TaskOutput: https://changelogs.core-directive.com/prompts/2.1.257/tools/TaskOutput.txt?arm=cli&config=flags-account
- TaskStop: https://changelogs.core-directive.com/prompts/2.1.257/tools/TaskStop.txt?arm=cli&config=flags-account
- TaskUpdate: https://changelogs.core-directive.com/prompts/2.1.257/tools/TaskUpdate.txt?arm=cli&config=flags-account
- WebFetch: https://changelogs.core-directive.com/prompts/2.1.257/tools/WebFetch.txt?arm=cli&config=flags-account
- WebSearch (changed in this version): https://changelogs.core-directive.com/prompts/2.1.257/tools/WebSearch.txt?arm=cli&config=flags-account
- Workflow: https://changelogs.core-directive.com/prompts/2.1.257/tools/Workflow.txt?arm=cli&config=flags-account
- Write: https://changelogs.core-directive.com/prompts/2.1.257/tools/Write.txt?arm=cli&config=flags-account

## Full text
- system prompt: https://changelogs.core-directive.com/prompts/2.1.257/system.txt?arm=cli&config=flags-account