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.

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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
v2.1.205	Claude_Code_v2.1.205/	54
v2.1.216	Claude_Code_v2.1.216/	53
v2.1.220	Claude_Code_v2.1.220/	64

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Changelog: v2.1.216 → v2.1.220

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Binary shrunk 258 MB → 253 MB (-5 MB) despite 11 new sections. 224,458 strings extracted. Major expansion in context management, autonomous loop, and tool prompts.

🆕 Added (11 new sections)

Section	Size	Description
managed_agents_ruby.txt	102.0 KB	Managed Agents Ruby SDK full README (embedded docs)
managed_agents_events.txt	80.5 KB	Managed Agents Events & Steering documentation
typescript_api_guide.txt	32.4 KB	Claude API TypeScript SDK guide
available_tools_guidance.txt	13.3 KB	"Check this list before writing" — tool selection guidance
advisor_tool_prompt.txt	9.8 KB	Advisor tool (stronger reviewer model) full prompt
plan_mode_reminder.txt	7.9 KB	"REMEMBER: You can ONLY explore and plan" — plan mode enforcement
browser_guidelines.txt	7.4 KB	Claude-in-Chrome browser automation guidelines
mcp_tab_group_tool.txt	7.3 KB	MCP tab group management tool
continue_session_prompt.txt	6.3 KB	Session continuation — restricts tool usage during resume
claude_md_structure.txt	4.9 KB	CLAUDE.md workflow structure definition
screenshot_tool_prompt.txt	4.1 KB	Screenshot tool description for Chrome automation

🚀 Major rewrites

• context_management.txt — 9.8 KB → 37.0 KB (+277%). Full background job session management, multi-session context windowing, compact service architecture.
• web_fetch.txt — 4.0 KB → 13.8 KB (+247%). Extended content extraction pipeline and readability processing.
• agents_sdk.txt — 4.5 KB → 13.7 KB (+207%). SDK agent identity expanded with sub-agent coordination.
• default_agent_prompt.txt — 4.5 KB → 13.7 KB (+202%). Richer tool-specific descriptions.
• autonomous_loop.txt — 7.6 KB → 17.2 KB (+126%). Revised escalation logic, enhanced PR maintenance workflow.
• memory_selection.txt — 1.3 KB → 8.0 KB (+513%). Massive expansion in memory selection rules.
• tool_denial_user.txt — 1.9 KB → 8.3 KB (+343%). Extended user-facing denial messages.
• exit_plan_mode.txt — 1.0 KB → 4.1 KB (+330%). Plan mode exit expanded.

➖ Significant shrinkage

• git_operations.txt — 2.1 KB → 0.3 KB (-85%). Git rules trimmed, likely consolidated.
• git_workflow.txt — 1.3 KB → 0.3 KB (-76%). Workflow guidance condensed.
• auto_mode_process.txt — 1.5 KB → 0.7 KB (-56%). Process flow simplified.
• claude_md_override.txt — 4.0 KB → 2.5 KB (-36%). Override rules condensed.

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Changelog: v2.1.205 → v2.1.216

Binary grew 247 MB → 258 MB (+11 MB). 217,961 strings extracted. One section removed, autonomous loop expanded, blast radius completely restructured.

🆕 Added

• New model identity strings: Fable 5, Opus 4.6+, Sonnet 4.6+ — Updated model tier references.
• statusline_agent.txt — Expanded 7× for agent status formatting.

🚀 Major rewrites

• blast_radius.txt — 4.4 KB → 16.1 KB (+266%). Now bundles the full system harness: System, Language, Output, Tools, Tone, Care sections in one file.
• autonomous_loop.txt — 4.9 KB → 7.8 KB (+58%). New escalation rule for 3 consecutive idle ticks, detailed PR maintenance workflow via GraphQL.
• default_agent_prompt.txt — 1.5 KB → 4.7 KB (+219%). Tool-specific descriptions added.
• explore_agent.txt — 1.0 KB → 2.5 KB (+153%). Exploration guidelines refined.
• todo_list_usage.txt — 2.0 KB → 4.2 KB (+111%). Task tracking rules expanded.

🔧 Restructured

• context_management.txt — 24.2 KB → 10.0 KB (-59%). Restructured, now references background job sessions.

🗑️ Removed

• creating_pull_requests.txt — Pull request creation instructions removed (merged into other sections).

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Changelog: v2.1.201 → v2.1.205

4-version jump. 28 new sections extracted. Major expansion in autonomous mode, new tool categories (MCP, skills, hooks, cron, web fetch), new agent identities (Agent SDK), and new guidance sections (plan vs memory, sandbox failures, commit/PR workflow, scratchpad directory).

🆕 Added (28 new sections)

• Agent identity expansion: agents_sdk, default_agent_prompt, capability_statement, interactive_agent_intro — Identity now split into four variants: CLI identity, Agent SDK identity, subagent default prompt, and interactive-mode intro. "You are highly capable" capability statement added as standalone section.
• autonomous_loop_tick — New dynamic pacing section for autonomous loop. Separate from main autonomous_loop content.
• Auto-mode trifecta: auto_mode_classifier, auto_mode_classifier_intro, auto_mode_process — Classifier now has its own standalone prompt, an intro/denial explanation, AND a classification review process section.
• Git/GitHub workflow: commit_messages_pr, creating_pull_requests, git_workflow — Commit message format, PR creation guidelines, and general git workflow extracted as separate sections.
• Plan mode expansion: plan_agent_specialist, plan_artifact_tool, plan_mode_instructions, plan_rejected_detail, plan_tool, plan_vs_memory, todo_list_usage, custom_workflow_body — Plan mode now has specialist agent prompts, artifact publishing, memory vs plan guidance, todo-list usage rules, and custom workflow body override.
• Hook system: hooks, hook_condition, stop_condition — Full hook event table (PostToolUse, etc.), condition evaluation prompt, and stop-condition verification prompt.
• MCP & Skills: mcp, skills, knowledge_mcp_search — MCP resource listing, skills delegation prompt, and MCP search strategy guidance.
• Web fetch: web_fetch, web_fetch_tool — Web fetch tool description + IMPORTANT usage notes (HTTPS upgrade, redirect handling).
• Chrome integration: chrome_browser_important, claude_in_chrome — Chrome browser IMPORTANT usage note + Claude in Chrome extension integration.
• Sandbox: sandbox_failure — Sandbox failure detection and recovery guidance.
• Context & memory: injected_context_notice, memory_selection, scratchpad_directory, todo_reminder — Context injection notice, memory selection prompt, scratchpad directory convention, and todo reminder (returned from v2.1.199).
• Tools: advisor_tool, send_message_tool, statusline_agent, tool_denial_user — Advisor tool description, SendMessage tool, statusline agent, and user-refusal handling.
• team_communication — Agent teammate communication section (extracted from team_comm).

✳️ Expanded / matured

• cyber_risk — Now includes Fable 5 / Mythos 5 identity paragraph and model tier description with link to anthropic.com/news.
• autonomous_loop — Clean extraction with full autonomous stewardship, PR maintenance, repeated invocation, and "spirit of the task" guidance.
• blast_radius — Full reversibility policy with destructive/hard-to-reverse/shared-state action examples.
• git_operations — Full git workflow with commit steps, parallel tool calls, and PR workflow.

🔧 Renamed / restructured

• identity_cli + identity_sdk + identity_agent → agents_sdk + default_agent_prompt + interactive_agent_intro
• simple_mode_intro → interactive_agent_intro (merged with system_harness)
• team_comm → team_communication
• plan_mode_guard → plan_rejected
• chrome_browser → chrome_browser_important
• coordinator, explore_agent, session_title, fable_unavailable, output_style_proactive, compact_service, context_management, exit_plan_mode, policy_spec, claude_md_override — content matches v2.1.201, extraction format differences only.

➖ Changed / merged

• system_harness — merged into interactive_agent_intro
• fable5_description — merged into cyber_risk (same binary chunk)
• tool_denial_guidance — split into tool_denial_guidance + tool_denial_user
• todo_reminder — returned (was dropped in v2.1.201, confirmed real in v2.1.205)
• plan_agent — returned (was dropped after v2.1.187)
• memory_selection — returned (was dropped after v2.1.187)
• statusline_agent — returned (was dropped after v2.1.195)
• auto_mode_classifier_intro — returned (was not extracted since v2.1.195)

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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.

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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

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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)

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