Claude Code - UC4N

Extracted system-prompt fragments from every version of Claude Code — archived version by version, with the new changes written up as news.

Each version lives in its own folder (Claude_Code_vX.Y.ZZZ/). The numbered .md files inside represent separate sections of the prompt (identity strings, agent prompts, tool descriptions, output styles, etc.).

Methodology note: Fragments are extracted from the claude.exe binary. Numeric prefixes can be re-numbered between versions, so the same number does not mean the same section — match sections by title/content. Also, extraction can sometimes leak binary string-table garbage into files (MIME lists, HTML-entity tables, symbol names), so a larger file size doesn't always mean more real content.

---

Versions

Version	Folder	Sections
v2.1.187	Claude_Code_v2.1.187/	33
v2.1.195	Claude_Code_v2.1.195/	26
v2.1.199	Claude_Code_v2.1.199/	27
v2.1.201	Claude_Code_v2.1.201/	26

---

Changelog: v2.1.187 → v2.1.195

Only verified / meaningful prompt changes are listed below. Most of the large byte increases in the v2.1.195 extraction (verification_agent 30 KB, auto_mode_classifier 28 KB, identity/fable 15 KB, todo_reminder, statusline) are extraction noise, not real prompt text, and have been filtered out.

🆕 Added

• 34_autonomous_loop — Autonomous / timer-invoked triggering. New fragment: "You're being invoked on a timer while…" Claude Code can now invoke itself on a timer, without user interaction. Lines up with scheduled cloud agents / routines and continuous agent-loop behavior.
• 35_agent_sdk_identity — Claude Agent SDK identity. New identity fragment: "running within the Claude Agent SDK." Signals an official SDK-embedded variant of Claude Code.
• New identity strings (inside identity_strings): in addition to the single line,
  • "You are Claude Code, Anthropic's official CLI for Claude, running within the Claude Agent SDK."
  • "You are a Claude agent, built on Anthropic's Claude Agent SDK."
• 04_doing_tasks_section — "Reversibility & blast radius" safety policy. This section was empty in the previous version; now it's populated: for actions that are hard to reverse or affect shared systems (git push, deleting branches, sending messages), ask the user first by default; a one-time approval doesn't count as standing approval.
• New model strings (inside claude_fable_unavailable): real model labels are now visible — "Fable 5, Opus 4.7+", "Fable 5, Opus 4.6+, Sonnet 4.6" — plus a "Use sparingly for the hardest tasks" (excessive tokens / overthinking) warning.

✳️ Expanded / matured

• 14_auto_mode_critique — grew from a single sentence into a 4-point structured rubric: Clarity, Completeness, Conflicts, Actionability. Reviews user-written allow/deny rules far more systematically.

➖ Not present in this extraction

The entire v2.1.195 folder was searched for the distinctive sentences of these sections; none had moved to another file. Whether this is an extraction-scope difference or a genuine removal can't be confirmed from this data alone.

• 17_output_style_learning (Learning output style)
• 26_plan_agent (read-only planning specialist prompt)
• 31_memory_selection (memory selector prompt)
• 32_github_issue_title (GitHub issue title generator)
• 33_team_coordination (team/teammate prompt)
• 09_agent_env_notes, 30_builtin_agents — no longer separate files (chrome content lives on in 21_chrome_browser_automation)
• 06_tone_conciseness, 25_js_prompt_assemblies — were already empty/placeholders; not a real loss

🔧 Minor / formatting

• 01_cyber_risk, 03_system_harness, 05_executing_actions, 07_git_operations, 10_explore_agent, 19_session_title, 21_chrome_browser_automation, 24_tool_prompts, 28_context_management: only a few dozen bytes of difference — no meaningful content change.
• 08_default_agent_prompt, 12_coordinator_system_prompt (§2), 02_simple_mode_intro: the v2.1.195 extraction is cut off mid-sentence; read this as an extraction truncation, not a content removal.

---

⭐ Highlights

1. Claude Agent SDK identity arrived — Claude Code now also positions itself as "running within the Agent SDK" / "a Claude agent built on the Agent SDK."
2. Autonomous / timer-invoked loop (34_autonomous_loop) — periodic self-invocation without a user.
3. New "reversibility & blast radius" policy — ask before destructive actions by default.
4. New model tier: Fable 5 (Opus 4.7+ / Opus 4.6+ + Sonnet 4.6), with an excessive-token warning.
5. Auto-mode rule critique matured — into a 4-dimension evaluation rubric.

---

Changelog: v2.1.195 → v2.1.199

Extraction format changed from numbered .md to descriptive .txt filenames. Section count increased to 27 (new sections extracted, some merged).

🆕 Added / newly extracted

• auto_critique — Auto-mode rule critique logic extracted as standalone section
• blast_radius — "Reversibility & blast radius" safety policy (was 04_doing_tasks_section in v2.1.195, now independent)
• claude_md_override — CLAUDE.md / project instructions override mechanism
• exit_plan_mode — Plan mode exit tool description
• policy_spec — <policy_spec> Bash command prefix detection rules
• tool_denial_guidance — Tool denial recovery guidance

✳️ Expanded

• coordinator — Now includes full §2 tools, §3 workers, §4 workflow, §5 concurrency, §6 verification sections
• autonomous_loop — Fuller extraction with timer invocation and repeated invocation sections
• explore_agent — Longer extraction with tool descriptions

🔧 Renamed / restructured

• 01_cyber_risk_instruction → cyber_risk
• 02_simple_mode_intro → simple_mode_intro
• 03_system_harness_section → system_harness
• 07_git_operations → git_operations
• 10_explore_agent → explore_agent
• 12_coordinator_system_prompt → coordinator
• 14_auto_mode_critique → auto_critique
• 19_session_title → session_title
• 20_todo_reminder → todo_reminder
• 21_chrome_browser_automation → chrome_browser
• 22_identity_strings → split into identity_cli, identity_sdk, identity_agent
• 23_claude_fable_unavailable → fable_unavailable + fable5_description
• 24_tool_prompts → absorbed into individual agent files
• 28_context_management → context_management
• 29_plan_mode_guard → plan_mode_guard
• 34_autonomous_loop → autonomous_loop
• 35_agent_sdk_identity → absorbed into identity_sdk

➖ Not present

• 06_tone_conciseness, 09_agent_env_notes, 11_verification_agent, 13_auto_mode_classifier_intro, 15_output_style_proactive, 16_output_style_explanatory, 17_output_style_learning, 18_compact_service, 25_js_prompt_assemblies, 26_plan_agent, 27_statusline_agent, 30_builtin_agents, 31_memory_selection, 32_github_issue_title, 33_team_coordination — extraction scope differences or content merges

---

Changelog: v2.1.199 → v2.1.201

Patch-level bump (2 versions). Most sections are identical or near-identical. Key meaningful changes below.

🆕 Added

• autonomous_loop — Major expansion. Now includes new guidance on broader scope: "following through on the spirit of the task they gave you, not just its literal scope", persistence ("Only stop if the original task is provably complete or the user said to stop"), and browser notification rules ("Keep the message under 200 characters, one line, no markdown. Lead with what they'd act on"). The "Repeated invocations" section was rewritten to bias toward broader scope exploration before quitting.

✳️ Expanded / matured

• simple_mode_intro — Rewritten intro text; now starts with "You work alongside the user on software engineering tasks" instead of the previous identity-first format
• plan_mode_guard — Wording changed around what tools are allowed in plan mode; exception clause expanded

🔧 Minor / formatting

• blast_radius, cyber_risk, fable5_description — Extraction format differences, core content unchanged
• Remaining sections show byte-level differences consistent with extraction noise rather than content changes

➖ Dropped

• todo_reminder — Not found in v2.1.201 extraction (was HTML entity false-positive in v2.1.199)

---

U-C4N