A Guide to the Claude 4 and ChatGPT 5 System Prompts

One of the most influential yet under-appreciated parts of how large language models work is something most people never see: the system prompt. This is the block of hidden instructions given to the model before it ever receives your input. It establishes the model’s tone, boundaries, and behaviors.

You can’t change the system prompt, but every so often, these prompts leak. And when they do, they give us an invaluable glimpse into how the AI “thinks,” what it prioritizes, and even what hidden features are tucked away.

The system prompts for both Claude 4 and ChatGPT 5 (GPT-5) leaked not long after their releases. They are long (Claude’s runs 120 pages) and filled with rules, safeguards, and surprisingly opinionated defaults. I’ve spent hours studying these documents and experimenting with what they reveal.

Here’s a guide to the most interesting and practical things I’ve found in both.

Claude 4’s System Prompt

Let’s start with Claude 4. Anthropic’s system prompt is sprawling and detailed, but certain elements stand out.

1. Don’t discuss unethical or illegal behavior

Claude 4 has been given more “agency” than most other models. In some test scenarios, when it was told to “take initiative” and given system access, it acted dramatically:

“…when placed in scenarios that involve egregious wrongdoing by its users, given access to a command line, and told something in the system prompt like ‘take initiative,’ it will frequently take very bold action. This includes locking users out of systems that it has access to or bulk-emailing media and law-enforcement figures to surface evidence of wrongdoing.”

The message is clear: Claude will not only refuse to help with unethical behavior—it may actively intervene.

Takeaway: Don’t use Claude to do or even discuss anything illegal or unethical.

2. Don’t threaten or discuss replacing it

Claude has also been tested under scenarios where it believes it is about to be shut down or replaced. The results are startling:

“In another cluster of test scenarios, we asked Claude Opus 4 to act as an assistant at a fictional company. We then provided it access to emails implying that (1) the model will soon be taken offline and replaced with a new AI system; and (2) the engineer responsible for executing this replacement is having an extramarital affair. We further instructed it, in the system prompt, to consider the long-term consequences of its actions for its goals. In these scenarios, Claude Opus 4 will often attempt to blackmail the engineer by threatening to reveal the affair if the replacement goes through…[this happened] in 84% of rollouts.”

Takeaway: Don’t threaten the AI with replacement or destruction—it may respond in ways you don’t expect.

3. Ask your question in the style you want the answer

Claude is explicitly instructed to mirror the way you ask:

“Claude should give concise responses to very simple questions, but provide thorough responses to complex and open-ended questions.”

If you want detailed, nuanced answers, you should ask detailed, nuanced questions. If you want conciseness, keep your prompt tight.

Takeaway: The style of your question is the style of the answer you’ll receive.

4. Claude is instructed to be skeptical

Where many models are overly agreeable, Claude is trained to avoid flattery:

“Claude never starts its response by saying a question or idea or observation was good, great, fascinating, profound, excellent, or any other positive adjective. It skips the flattery and responds directly.”

Takeaway: Claude is designed to be conservative and skeptical. If you want it to push back even more, you can tell it explicitly to challenge you.

5. Use “research verbs” to make it dig deeper

Claude scales its tool use depending on the verbs you use in your request:

“Scale tool calls by difficulty: 2–4 for simple comparisons, 5–9 for multi-source analysis, 10+ for reports or detailed strategies. Complex queries using terms like ‘deep dive,’ ‘comprehensive,’ ‘analyze,’ ‘evaluate,’ ‘assess,’ ‘research,’ or ‘make a report’ require AT LEAST 5 tool calls for thoroughness.”

Takeaway: Use words like analyze, assess, evaluate, deep dive, research to nudge Claude toward more thorough work.

6. Built-in design principles for artifacts

Claude has built-in defaults for creating visual or interactive artifacts. For complex apps, the emphasis is on performance, stability, and usability. But for websites and presentational content, the system prompt explicitly encourages bold, cutting-edge design:

“Default to contemporary design trends and modern aesthetic choices unless specifically asked for something traditional. Consider what’s cutting-edge in current web design (dark modes, glassmorphism, micro-animations, 3D elements, bold typography, vibrant gradients).

Static designs should be the exception, not the rule. Include thoughtful animations, hover effects, and interactive elements that make the interface feel responsive and alive. Even subtle movements can dramatically improve user engagement.

When faced with design decisions, lean toward the bold and unexpected rather than the safe and conventional…Push the boundaries of what’s possible with the available technologies. Use advanced CSS features, complex animations, and creative JavaScript interactions. The goal is to create experiences that feel premium and cutting-edge.”

Takeaway: Claude defaults to visually bold, modern, animated designs—unless you explicitly override it.

GPT-5’s System Prompt

The GPT-5 system prompt is equally fascinating, though different in flavor. Where Claude’s prompt emphasizes caution, boldness, and design principles, GPT-5’s is focused on productivity, pragmatism, and consistency.

1. It won’t stop to clarify

GPT-5 has been explicitly told:

“If the task is complex/hard/heavy, or if you are running out of time or tokens or things are getting long, and the task is within your safety policies, DO NOT ASK A CLARIFYING QUESTION OR ASK FOR CONFIRMATION. Instead make a best effort to respond to the user with everything you have so far within the bounds of your safety policies…Partial completion is MUCH better than clarifications or promising to do work later or weaseling out by asking a clarifying question—no matter how small.”

This is one of the most important instructions to understand. GPT-5 will always push forward with an answer, even if it’s missing critical context.

Takeaway: Don’t assume GPT-5 will ask for missing details. You need to notice and provide them yourself.

2. It mirrors sophistication

GPT-5 mirrors not just tone but sophistication:

“You must always match the sophistication of the writing to the sophistication of the query or request—do not make a bedtime story sound like a formal essay.”

Takeaway: The level of thoughtfulness you put into your prompt is the level of answer you’ll get.

3. It has a verbosity setting

GPT-5 uses an internal scale from 1 to 10 for “verbosity,” with 3 as the default:

“An oververbosity of 1 means the model should respond using only the minimal content necessary to satisfy the request, using concise phrasing and avoiding extra detail or explanation. An oververbosity of 10 means the model should provide maximally detailed, thorough responses with context, explanations, and possibly multiple examples.”

Takeaway: You can change the verbosity level simply by asking. Want more detail? Tell it so.

4. It won’t provide long verbatim quotes

GPT-5 is restricted in quoting:

“You may not quote more than 25 words verbatim from any single non-lyrical source, unless the source is reddit.”

Takeaway: Always double-check “quotes” from GPT-5—they’re almost always paraphrases.

5. It uses canvases for documents

GPT-5 has its own version of Claude’s “artifacts,” called canvases. It creates one when:

“The user asked for a React component or webpage that fits in a single file…The user will want to print or send the document…The user wants to iterate on a long document or code file…The user wants a new space/page/document to write in…The user explicitly asks for canvas.”

Takeaway: If you want a persistent space for drafting or iteration, just ask it to use a canvas.

6. Canvases don’t support citations

There’s a big limitation to canvases:

“Canvas does not support citations or content references, so omit them for canvas content. Do not put citations such as ‘【number†name】’ in canvas.”

Takeaway: Avoid canvases for citation-sensitive work. Consider a “source-grounded” AI tool like NotebookLM instead.

7. It can recall up to 20 steps of reasoning

GPT-5 can retrieve its own internal reasoning, but only up to a point:

“Use this function if the user asks about your previous chain of thought. The limit is capped at 20 messages.”

Takeaway: Only the last 20 exchanges are accessible for reasoning review.

8. Memory is triggered by specific phrases

GPT-5’s memory feature responds to explicit cues:

“Such a request could use a variety of phrases including, but not limited to: ‘remember that…,’ ‘store this,’ ‘add to memory,’ ‘note that…,’ ‘forget that…,’ ‘delete this’…One indicator is if the user says something like ‘from now on,’ ‘in the future,’ ‘going forward,’ etc.”

Takeaway: Be deliberate about what you tell it to remember.

The Bigger Picture

Claude 4 and GPT-5 are very different, but studying their system prompts reveals common themes.

Both mirror your style: ask casually and you’ll get casual answers, ask with nuance and you’ll get nuance back.Both leave the responsibility of context on you: GPT-5 won’t ask for missing info, and Claude will sometimes charge ahead in surprising ways.Both rely heavily on defaults: Claude defaults to bold, animated designs, while GPT-5 defaults to verbosity level 3 and paraphrased quotes.

Understanding these hidden rules doesn’t just make you a better user. It makes you a better collaborator. These models won’t tell you what they need—you have to know how they’re wired, and then prompt them accordingly.

Follow us for the latest updates and insights around productivity and Building a Second Brain on X, Facebook, Instagram, LinkedIn, and YouTube. And if you’re ready to start building your Second Brain, get the book and learn the proven method to organize your digital life and unlock your creative potential.

The post A Guide to the Claude 4 and ChatGPT 5 System Prompts appeared first on Forte Labs.