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Sweep 22 Sep 2026 · 17:19Z Build v2.1.280 501 read Stable v2.1.267 Latest v2.1.280 Next v2.1.280 Feeds RSS JSON llms.txt Unofficial
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Prompt capture

v2.1.257, what moved

CLI Claude Code, interactive mode, seeded with flags-anon. 1 added and 1 removed, of 223 lines, about 4 words, in the prompt 17 of 27 arms receive. 3 other prompts also changed. 1 of 30 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.

This arm was captured with the sandbox seeded from flags-anon, the anonymous GrowthBook payload, seeded into the sandbox .claude.json. 577 flags from data/flags/snapshots/flags-20260901T155505Z.json. What a seeded capture does and does not tell you.

Releasedcaptured
Compared withv2.1.252the previous capture on this arm
Prompt223 ln4 families, 27,313 characters
Model strings27every capture asks all of them
Tool descriptions30 2 moved this release, 28 with a parameter schema
Appended after it3 blocks25,410 more characters on the wire This changeas markdownfor diffing it yourself
Claude Code, interactive mode Agent SDK, print mode Claude Code, interactive mode, seeded with flags-account Claude Code, interactive mode, seeded with flags-anon Agent SDK, print mode, seeded with flags-account Agent SDK, print mode, seeded with flags-anon
6 capture arms for this release, one page each, never diffed against each other

What changed since the previous capture

5 One line per document that moved, the system prompt and the tool descriptions in the same table.
PromptReachMovedThe first line that changed
System prompt 223 ln, and 17 other copies of it moved the same way 20 of 27 arms +1−1 - 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: 'cla...
System prompt 76 ln, and 1 other copy of it moved the same way 6 of 27 arms +2−3 - 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: 'cla...
System prompt 85 ln 1 of 27 arms +2−2 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 abo...
WebSearch 27 ln 17 of 27 arms +1−1 - The current month is August 2026. You MUST use this year when searching for recent information, documentation, or current events.
WebSearch 5 ln 10 of 27 arms +1−1 - The current month is August 2026 — use this when searching for recent information.

The families in this capture

4 A family is one prompt and every model-interpolated copy of it, ranked by the model strings it reaches.
#FamilyHeadReachCopiesOpens with
1 Sonnet 5 family, 3 model strings 223 ln · 27.3k 17 of 27 15 copies You are an interactive agent that helps users with software engineering tasks.
2 claude-fable-5 85 ln · 10.4k 2 of 27 2 copies You are an interactive agent that helps users with software engineering tasks.
3 Opus family, 5 model strings 76 ln · 9.4k 6 of 27 2 copies You are an interactive agent that helps users with software engineering tasks.
4 Opus 4.8 62 ln · 6k 2 of 27 2 copies You are an interactive agent that helps users with software engineering tasks.

Tool descriptions

30 The text the model is given for each tool, on this arm.
All 30 tool descriptions →
ToolDescriptionCopiesMoved
Agent 1,811 chars 2 ○same
AskUserQuestion 1,786 chars 2 ○same
Bash 1,366 chars 19 ○same
CronCreate 2,595 chars 1 ○same
CronDelete 100 chars 1 ○same
CronList 60 chars 1 ○same
Edit 360 chars 2 ○same
EnterPlanMode 4,011 chars 1 ○same
EnterWorktree 3,220 chars 1 ○same
ExitPlanMode 1,849 chars 1 ○same
ExitWorktree 1,923 chars 1 ○same
ListAgents 777 chars 1 ○same
Monitor 6,132 chars 1 ○same
NotebookEdit 619 chars 1 ○same
PushNotification 1,362 chars 1 ○same
Read 790 chars 2 ○same
ReportFindings 574 chars 1 ○same
ScheduleWakeup 3,396 chars 1 ○same
SendMessage 3,386 chars 1 ○same
Skill 1,417 chars 1 ○same
TaskCreate 2,146 chars 1 ○same
TaskGet 732 chars 1 ○same
TaskList 998 chars 1 ○same
TaskOutput 1,049 chars 1 ○same
TaskStop 378 chars 1 ○same
TaskUpdate 2,243 chars 1 ○same
WebFetch 374 chars 2 ○same
WebSearch 312 chars 2 ◆moved
Workflow 3,480 chars 1 ○same
Write 240 chars 2 ○same
Read the whole system prompt → - 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...
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