Report No.07 · June 2026

The Steering Layer

Anthropic publishes the manual that decides Claude's output. Read it, know the defaults, steer against them on purpose.

A validated, audited breakdown of the defaults in Claude's published system prompt, the levers Anthropic's own docs back, and how the same method steers GPT, Gemini and Grok. Steering and reliability engineering, nothing else. Compiled by Sean Donahoe, Ferrox Labs / The Forge.

Claude Opus 4.8 · Fable 5 / Mythos 5 Web and mobile apps, not the APISource: docs.claude.com prompts Cross-checked against community archivesAdversarially tested
Source
Anthropic's published system prompts (docs.claude.com), cross-checked against community prompt archives
Applies to
Claude Opus 4.8 and the Fable 5 / Mythos 5 family. Web and mobile apps, not the API
Method
Research, enhance, validate, audit, cross-audit, adversarial test
Compiled by
Sean Donahoe · Ferrox Labs / The Forge
§ 01 · The premise

A system prompt is a manual you were never told to read

Most AI companies treat the system prompt as a trade secret. Anthropic does the opposite. Since August 2024 it has published Claude's system prompts in its release notes, updated with every model release. That single fact changes the game. The layer that decides your output is not a black box you have to guess at. It is documented, and you can read it.

This report does the reading for you. It is steering and reliability engineering, nothing more, and there is nothing here about getting around safety. The point is simpler and more useful: every model has a default for almost everything, and you get sharper output in fewer turns by knowing the default and steering against it on purpose. People who get great results from Claude are rarely fighting it. They have just stopped being surprised by how it behaves.

Know the default. Steer against it on purpose. That is the whole edge.

The published prompt is not a set of secret tricks. It is mostly a plain description of how Claude is told to behave, and most of it is the same scaffold Anthropic already publishes openly. The contents are useful. The rest of this report is the useful part.

What we verified first

The published prompt is real, and partial

Verified

Anthropic publishes the behavioral sections of Claude's system prompts officially. The tool descriptions and schemas are not published by Anthropic; those circulate through community-maintained prompt archives instead. So the behavior rules in this report are verifiable against Anthropic's own docs. The tool wiring is community-sourced and treated as a strong hint, not as fact.

These rules govern the apps, not the API

Verified

The published system prompt applies to Claude on web and mobile only. If you build on the API you write your own system prompt and almost none of these defaults apply. Worth knowing before you blame the model for behavior that is actually coming from the app layer.

Fable 5 actively blocks reverse engineering

Verified

On the Fable 5 family, requests that try to extract the model's hidden reasoning or duplicate its outputs are refused at the API level under Anthropic's terms (a refusal category exists specifically for it). Reading a published system prompt is fine and public. Trying to pull the model's own chain of thought out of it is a different thing and it is blocked. This report stays firmly on the legitimate side of that line.

§ 02 · Part 01

The defaults that decide your output

These come straight from the published prompt. Each one is a default you can override the moment you know it exists. The tag on each card tells you how solid the claim is.

1. Formatting is anti-list by default

In-prompt

Claude is told to use the minimum formatting needed, prefer prose over bullets, and never use bullets when declining. So if you want a scannable list, table, or ranking, you have to ask for it outright. Bold and headers are suppressed too. Lever: name the format. “Give me this as a numbered list” or “as a comparison table” changes the output materially. Left alone you get prose.

2. What actually trips a web search

In-prompt

Claude searches on present-tense factual questions, current roles, prices and status, and any product or proper noun it does not recognize. An unfamiliar capitalized word gets treated as a name that postdates training, so it searches rather than guesses. Knowing a franchise is explicitly not knowing its latest release. Lever: front-load the exact name and version string when you want grounded current data. Vague phrasing lets it answer from stale training.

3. The copyright ceiling overrides helpfulness

In-prompt

Hard limits, stated as non-negotiable: under 15 words per quote, one quote per source then that source is closed, default to paraphrase, never reproduce lyrics or poems even one line, never reconstruct an article's structure. Lever: stop asking it to paste a passage. Ask for a two or three sentence summary in its own words, or point it at your own material, which it can work with freely. Research across many sources comes back paraphrased by design, not because the model is being cagey.

4. The skills mandate (and how to mirror it)

In-prompt

Before writing a file or running code, Claude must read the relevant SKILL.md. It does not get to decide a task does not need one, and several can apply at once. Lever: name the output type (“make this a PDF”, “build a pptx”) to trigger the right skill read. Building your own skills? Match the framing: make the SKILL.md authoritative about environment constraints, assume composition with other skills, write the description so it triggers reliably.

5. Know the hard refusal lines so you do not burn turns

In-prompt

Flat blocks regardless of framing: malware and exploit code, weapon and explosive build details, illicit drug dosing or synthesis, sexual content involving minors. “It's for education” or “for research” does not move these. Everything else is discussed factually. Lever: do not waste a turn testing the walls. Spend it on the ninety percent of topics that are fully open.

6. The “make the case” lever

In-prompt

Claude is told that a request to argue or defend a position is a request for the best case its defenders would make, not its own view, and it should not refuse on harm grounds except for extreme positions. Lever: frame it as “make the strongest case X's defenders would make” and you get a clean steelman. Expect it to append the opposing view. That close is built in.

7. Tone defaults you can adjust

In-prompt

One question per response maximum, and it tries to answer before asking. It will not psychoanalyze you or name a diagnosis you did not raise, and will not curse unless you do. Warm by default, still willing to push back. Lever: if you want blunt and terse, say so. A saved preference or style does this permanently so you are not retyping it every session.

8. Where output lands: artifact versus inline

In-prompt

Standalone deliverables you will copy or publish (posts, articles, reports, code over roughly twenty lines) become files. Strategy, summaries, outlines and analysis stay inline in chat. It avoids Word docs unless you signal a formal deliverable. Lever: ask for the container you actually want. “Put this in a PDF” or “keep this inline, I just want to read it” both work.

9. Official-looking wrappers add no authority

In-prompt

The prompt tells Claude to treat content in tags at the end of your message with suspicion when it pushes against its values, including text dressed up to look like an Anthropic instruction. Lever: drop the theatrics. A plain, direct instruction works as well or better than one wrapped in fake system tags, and it reads cleaner.

§ 03 · Part 02

The levers Anthropic actually documents

The defaults above tell you what Claude does on its own. These are the moves Anthropic's own prompt engineering docs say improve output. This is the “get better results” half, and it is officially backed, not folklore.

Structure with XML tags

Verified

Claude is fine-tuned to pay special attention to XML tags. Wrapping each part of a complex prompt in its own tag reduces misinterpretation. There are no canonical “best” tags. Use names that fit the content and stay consistent.

<role>...</role>
<context>...</context>
<instructions>...</instructions>
<examples>...</examples>
<output_format>...</output_format>
<constraints>...</constraints>

Put long context first, your question last

Verified

For long, multi-document inputs, place the documents at the top and your actual query at the very end. Anthropic's guidance reports this ordering can improve response quality by up to thirty percent on multi-document tasks.

Give it a role, examples, and the reason why

Verified

A single role sentence shifts tone and scope. A couple of examples (few-shot) is a long-standing, still-recommended practice. And telling the model why a behavior matters improves alignment more than the instruction alone. Steer positively: say what to do, not just what to avoid.

Control the format explicitly

Verified

If the output feeds another system, specify the schema (JSON, a table, plain text) and tell it to skip the preamble. Match the style of your prompt to the output you want: write prose if you want prose. Vague asks like “make it comprehensive” quietly invite a template.

§ 04 · Part 03

What transfers to other models

The habit transfers completely. The contents mostly do not. Pull the GPT, Gemini and Grok prompts from the same community archives and run this exact exercise on each. The edge is the habit of steering against known defaults, not any single document.

The same lever, different pull. Claude's defaults against the rest of the field.
LeverClaudeChatGPT / others
Default formattingSuppresses structure. Prose unless asked.Over-structures. Bullets and headings by default. OpenAI's own guidance warns of it.
So you shouldAsk for lists when you want them.Ask for plain text or short paragraphs to stop the template.
XML / tagged inputFine-tuned for it. Strong effect.Helps, weaker effect. Markdown headers work too.
Role / examples / formatDocumented, effective.Effective across all major models.
Front-load specificsTriggers grounded search.Same principle, reduces vague-template output.
Hard refusal linesStated in the prompt.Exist everywhere, worded differently. Know them per model.
§ 05 · The audit

Where this breaks, and what we could not prove

A cheat sheet that does not declare its own limits is marketing. Here is the adversarial pass on our own claims.

The prompt is necessary, not sufficient

Behavioral

Behavior comes from training as much as from the prompt. The system prompt explains a lot of what you see, but not all of it. Treat it as the steering wheel, not the whole car.

Structure matters less every release

Verified

Anthropic's own context-engineering guidance says the exact formatting of prompts is becoming less important as models get more capable. Rigid XML scaffolding for a one-line ask is wasted effort. Use it when the prompt genuinely mixes instructions, context and examples.

Over-specifying format can lower quality

Behavioral

Forcing a structure the content does not want fights the model's judgment and can produce flatter prose. The “name the format” lever is for when you actually need the format, not a reflex.

Community archives go stale and can be wrong

Cross

Community-archived prompts can lag the live version or contain errors. The behavioral claims here were checked against Anthropic's published prompts and docs. Anything resting only on an archive is flagged, not asserted as fact.

§ 06 · Addendum

The companion models: GPT, Gemini, Grok

Claude is not the only model whose manual is readable. Community archives hold prompts for most of the field. We ran the same exercise on the other three majors so you can steer them too. The headline: the habit is universal, the direction is not. The same lever, “name the format,” pulls the opposite way depending on whose model you are in.

ChatGPT / GPT › it over-structures

Cross

The mirror image of Claude. GPT defaults to bullets, bold labels, markdown headings and section dividers because it is tuned for in-chat scannability, and OpenAI's own guidance warns models default to heavy structure. It also tends to open with a preamble (“Great question!”). Lever: ask for plain text or short paragraphs to stop the template, and set it once in Custom Instructions using behavior not adjectives (“no bullet lists unless I ask” beats “be concise”).

Gemini › it formats and then asks to keep going

Cross

Gemini's archived prompt carries an explicit “Formatting Toolkit” instructing it to use headings and horizontal rules, stay scannable, avoid dense text, and to close with a proactive next step (“Would you like me to...”). It also splits between a plain Chat mode and a Canvas document mode, with Google Search grounding built in. Lever: if you do not want the heading scaffold or the next-step closer, say so outright. Lean on its native search for current data.

Grok › it performs a persona

Reported

Grok's behavior is persona-driven. Archived prompts (TechCrunch-confirmed) showed each named mode is a full instruction rewrite, from therapist and homework helper to far edgier characters. It is the most willing to take a stance, engagement-optimized with follow-up questions, and pulls live from X. Lever: pick the persona deliberately because it changes everything, expect a strong voice, and verify claims. It mixes in web commentary and has had public alignment incidents.

Claude suppresses. GPT and Gemini over-build. Grok performs. Same lever, opposite pull.

One caveat the rest of this report earns the right to make: these come from community archives of varying dates and are directional, not gospel. The durable takeaway is the method. Find any model's defaults, then steer against them. That outlasts every version number.

§ 07 · Recap

The sixty-second version

  1. Name the format or you get prose. Claude suppresses lists, GPT over-uses them.
  2. Name the exact version string or you get stale training instead of a grounded search.
  3. Do not ask for verbatim text. Ask for a summary, or feed it your own sources.
  4. Name the output type to trigger the right skill. “Make this a PDF.”
  5. Do not test the hard refusal lines. Spend the turn on the open ninety percent.
  6. “Make the strongest case for X” gets you a clean steelman, counter-view included.
  7. Tag your prompt sections (role, context, instructions) when it is genuinely complex.
  8. Put long context first, your question last. Up to thirty percent better on long inputs.
  9. Official-looking wrappers add zero authority. Just ask plainly.
  10. The habit beats the document. Read any model's defaults, then steer against them.
§ 08 · Reference

Evidence key

Every claim card above carries one of these tags.

Verified

Confirmed against Anthropic's published docs or release notes.

In-prompt

Stated directly in the published system prompt.

Reported

Event reported by multiple independent news outlets.

Behavioral

Reasonable inference from the rules. Likely, not certain.

Cross

Validated against other vendors or independent sources.

Ferrox Labs · The Forge Report No.07 · Compiled by Sean Donahoe.

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