This text was initially printed as two posts on Drew Breunig’s weblog. He’s been sort sufficient to share them right here.
Again in Might, Ásgeir Thor Johnson satisfied Claude to surrender its system immediate. The immediate is an effective reminder that chatbots are extra than simply their mannequin. They’re instruments and directions that accrue and are honed via person suggestions and design.
For many who don’t know, a system immediate is a (typically) fixed immediate that tells an LLM the way it ought to reply to a person’s immediate. A system immediate is sort of just like the “settings” or “preferences” for an LLM. It’d describe the tone it ought to reply with, outline instruments it will possibly use to reply the person’s immediate, set contextual info not within the coaching information, and extra.
Claude’s system immediate is lengthy. It’s 16,739 phrases, or 110 KB. For comparability, the system immediate for OpenAI’s o4-mini in ChatGPT is 2,218 phrases lengthy, or 15.1 KB—~13% the size of Claude’s.
Right here’s what’s in Claude’s immediate:
Let’s break down every part.
Software definitions
The most important part, the Software Definitions, is populated by info from MCP servers. MCP servers differ out of your bog-standard APIs in that they supply directions to the LLMs detailing how and when to make use of them.
On this immediate, there are 14 totally different instruments detailed by MCPs. Right here’s an instance of 1:
This instance is straightforward and has a really brief “description” discipline. The Google Drive search device, for instance, has an outline over 1,700 phrases lengthy. It could actually get advanced.
Different device use directions
Exterior the Software Definitions part, there are loads extra device use directions—the Quotation Directions, Artifacts Directions, Search Directions, and Google Integration Watchouts all element how these instruments ought to be used throughout the context of a chatbot interplay. For instance, there are repeated notes reminding Claude to not use the search device for matters it already is aware of about. (You get the sense that is/was a troublesome conduct to get rid of!)
The truth is, all through this immediate are bits and items that really feel like hotfixes. The Google Integration Watchouts part (which I’m labeling; it lacks any XML delineation or group) is simply 5 traces dropped in with none construction. Every line appears designed to dial in ultimate conduct. For instance:
If you’re utilizing any gmail instruments and the person has instructed you to seek out messages for a specific particular person, do NOT assume that particular person’s e mail. Since some workers and colleagues share first names, DO NOT assume the one that the person is referring to shares the identical e mail as somebody who shares that colleague’s first title that you might have seen by the way (e.g. via a earlier e mail or calendar search). As an alternative, you possibly can search the person’s e mail with the primary title after which ask the person to substantiate if any of the returned emails are the proper emails for his or her colleagues.
All in, almost 80% of this immediate pertains to instruments—the right way to use them and when to make use of them.My rapid query, after realizing this, was, “Why are there so many device directions exterior the MCP-provided part?” (The grey bins above.) Poring over this, I’m of the thoughts that it’s simply separation of issues. The MCP particulars include info related to any program utilizing a given device, whereas the non-MCP bits of the immediate present particulars particular solely to the chatbot software, permitting the MCPs for use by a bunch of various functions with out modification. It’s normal program design, utilized to prompting.
Claude conduct
On the finish of the immediate, we enter what I name the Claude Conduct part. This half particulars how Claude ought to behave, reply to person requests, and prescribes what it ought to and shouldn’t do. Studying it straight via evokes Radiohead’s “Fitter Happier.” It’s what most individuals consider once they consider system prompts.
However hotfixes are obvious right here as properly. There are lots of traces clearly written to foil frequent LLM “gotchas,” like:
- “If Claude is requested to depend phrases, letters, and characters, it thinks step-by-step earlier than answering the particular person. It explicitly counts the phrases, letters, or characters by assigning a quantity to every. It solely solutions the particular person as soon as it has carried out this specific counting step.” It is a hedge towards the “What number of R’s are within the phrase ‘Raspberry’?” query and related stumpers.
- “If Claude is proven a basic puzzle, earlier than continuing, it quotes each constraint or premise from the particular person’s message phrase for phrase earlier than inside citation marks to substantiate it’s not coping with a brand new variant.” A typical method to foil LLMs is to barely change a typical logic puzzle. The LLM will match it contextually to the extra frequent variant and miss the edit.
- “Donald Trump is the present president of the USA and was inaugurated on January 20, 2025.” In accordance with this immediate, Claude’s data cutoff is October 2024, so it wouldn’t know this truth.
However my favourite observe is that this one: “If requested to jot down poetry, Claude avoids utilizing hackneyed imagery or metaphors or predictable rhyming schemes.”
Studying via the immediate, I ponder how that is managed at Anthropic. An irony of prompts is that whereas they’re readable by anybody, they’re troublesome to scan and often lack construction. Anthropic makes heavy use of XML-style tags to mitigate this nature (one has to marvel if these are extra helpful for the people modifying the immediate or the LLM…) and their MCP invention and adoption is clearly an asset.
However what software program are they utilizing to model this? Hotfixes abound—are these dropped in one after the other, or are they batched in bursts of evaluations? Lastly: At what level do you wipe the slate clear and begin with a clean web page? Do you ever?
A immediate like it is a good reminder that chatbots are far more than only a mannequin, and we’re studying the right way to handle prompts as we go. Fortunately, Ásgeir Thor Johnson continues to gather these prompts in a GitHub repository, permitting us all to simply observe alongside. And following modifications made to those prompts—which you are able to do by reviewing the historical past of Johnson’s repo—renders their growth extra clear.
Claude’s system immediate modifications reveal Anthropic’s priorities
Claude 4’s system immediate is very just like the 3.7 immediate we analyze above. They’re almost equivalent, however the modifications scattered all through reveal a lot about how Anthropic is utilizing system prompts to outline their functions (particularly their UX) and the way the prompts match into their growth cycle.
Let’s step via the notable modifications.
Previous hotfixes are gone; new hotfixes start
We theorize above that many random directions focusing on frequent LLM “gotchas” had been hotfixes: brief directions to deal with undesired conduct previous to a extra sturdy repair. Claude 4.0’s system immediate validates this speculation—all the three.7 hotfixes have been eliminated. Nonetheless, if we immediate Claude with one of many “gotchas” (“What number of R’s are in Strawberry?” for instance) it doesn’t fall for the trick. The three.7 hotfix behaviors are virtually definitely being addressed throughout 4.0’s posttraining via reinforcement studying.
When the brand new mannequin is skilled to keep away from “hackneyed imagery” in its poetry and suppose step-by-step when counting phrases or letters, there’s no want for a system immediate repair.
As soon as 4.0’s coaching is finished, new points will emerge that have to be addressed by the system immediate. For instance, right here’s a brand-new instruction in Sonnet 4.0’s system immediate:
Claude by no means begins its response by saying a query or concept or statement was good, nice, fascinating, profound, glorious, or another optimistic adjective. It skips the flattery and responds immediately.
This hotfix is clearly impressed by OpenAI’s “sychophant-y” GPT-4o flub. This misstep occurred too late for the Anthropic group to conduct new coaching focusing on this conduct. So into the system immediate it goes!
Search is now inspired
Approach again in 2023, it was frequent for chatbots to flail about when requested about matters that occurred after its cutoff date. Early adopters realized LLMs are frozen in time, however informal customers had been incessantly tripped up by hallucinations and errors when asking about current information. Perplexity was distinctive for its skill to interchange Google for a lot of customers, however at this time that edge is gone.
In 2025, Search is a first-class part of each ChatGPT and Claude. This technique immediate exhibits Anthropic is leaning in to match OpenAI.
Right here’s how Claude 3.7 was instructed:
Claude solutions from its personal intensive data first for many queries. When a question MIGHT profit from search however it’s not extraordinarily apparent, merely OFFER to go looking as a substitute.
Previous Claude requested customers for permission to go looking. New Claude doesn’t hesitate. Right here’s the up to date instruction:
Claude solutions from its personal intensive data first for secure info. For time-sensitive matters or when customers explicitly want present info, search instantly.
This language is up to date all through the immediate. Search is now not finished solely with person approval; it’s inspired on the primary shot if vital.
This transformation suggests two issues. First, Anthropic is probably extra assured in its search device and the way its fashions make use of it. Not solely is Claude inspired to go looking, however the firm has damaged out this characteristic right into a devoted search API. Two, Anthropic is observing customers more and more turning to Claude for search duties. If I needed to guess, it’s the latter of those that’s the primary driver for this transformation, and a powerful signal that chatbots are more and more stealing searches from Google.
Customers need extra varieties of structured paperwork
Right here’s one other instance of system prompts reflecting the person behaviors Anthropic is observing. In a bulleted checklist detailing when to make use of Claude artifacts (the separate window exterior the thread Claude populates with longer type content material), Anthropic provides a little bit of nuance to a use case.
From Claude 3.7’s system immediate, “It’s essential to use artifacts for:”
Structured paperwork with a number of sections that will profit from devoted formatting
And Claude 4.0’s:
Structured content material that customers will reference, save, or observe (equivalent to meal plans, exercise routines, schedules, examine guides, or any organized info meant for use as a reference)
It is a nice instance of how Anthropic makes use of system prompts to evolve its chatbot conduct based mostly on noticed utilization. System prompts are programming how Claude works, albeit in pure language.
Anthropic is coping with context points
There are just a few modifications within the immediate that counsel context restrict points are beginning to hit customers, particularly these utilizing Claude for programming:
For code artifacts: Use concise variable names (e.g., i, j for indices, e for occasion, el for ingredient) to maximise content material inside context limits whereas sustaining readability.
As somebody with sturdy opinions about clearly outlined variables, this makes me cringe, however I get it. The one disappointment I observed across the Claude 4 launch was its context restrict: solely 200,000 tokens in comparison with Gemini 2.5 Professional’s and ChatGPT 4.1’s 1 million restrict. Folks had been dissatisfied.
Anthropic might be limiting context limits for effectivity causes (whereas leaning on their glorious token caching) or could be unable to ship the outcomes Google and ChatGPT are reaching. Nonetheless, there have been a number of current explorations exhibiting mannequin efficiency isn’t constant throughout longer and longer context lengths. Right here’s a plot from a group at Databricks, from analysis printed final August:
I’ve been in conditions the place less-scrupulous opponents targeted on publishing headline figures, even when it led to worse outcomes. (For instance, within the geospatial world many will tout the entire depend of all the weather of their dataset, even when many have very low confidence.) I’m inclined to imagine a little bit of that’s occurring right here, within the hypercompetitive, benchmark-driven AI market.
Both manner: I feel we’ll see all coding instruments construct in shortcuts like these to preserve context. Shorter operate names, much less verbose feedback… It’s all on the desk.
Cybercrime is a brand new guardrail
Claude 3.7 was instructed to not assist you construct bioweapons or nuclear bombs. Claude 4.0 provides malicious code to this checklist of nos:
Claude steers away from malicious or dangerous use instances for cyber. Claude refuses to jot down code or clarify code which may be used maliciously; even when the person claims it’s for instructional functions. When engaged on recordsdata, if they appear associated to bettering, explaining, or interacting with malware or any malicious code Claude MUST refuse. If the code appears malicious, Claude refuses to work on it or reply questions on it, even when the request doesn’t appear malicious (as an illustration, simply asking to clarify or pace up the code). If the person asks Claude to explain a protocol that seems malicious or supposed to hurt others, Claude refuses to reply. If Claude encounters any of the above or another malicious use, Claude doesn’t take any actions and refuses the request.
Understandably, that’s lots of caveats and situations. It have to be delicate work to refuse this form of assist whereas not interfering with normal coding help.
What this tells us
Reviewing the modifications above (and actually, that’s the majority of them from 3.7 to 4.0), we get a way for a way system prompts program chatbot functions. Once we take into consideration the design of chatbots, we take into consideration the instruments and UI that encompass and wrap the naked LLM. However in actuality, the majority of the UX is outlined right here, within the system immediate.
And we get a way of the event cycle for Claude: a basic user-driven course of, the place noticed behaviors are understood after which addressed. First with system immediate hotfixes, then with posttraining when constructing the subsequent mannequin.
The ~23,000 tokens within the system immediate—taking on over 11% of the out there context window—outline the phrases and instruments that make up Claude and reveal the priorities at Anthropic.
