The Claude Fable 5 Field Guide: 8 "Finding Your Unknowns" Prompt Patterns, From Blind Spot Scans to Post-Read Quizzes

A talk transcript from Claude Code team member Thariq Shihipar: the bottleneck with new models is no longer the model itself — it's whether you can clearly articulate your own unknowns
By AI Engineer 大会 / Anthropic07-07 · 11 min read⚑ Tutorial / how-to
Deep Dive · XiaoHu Explains
TL;DR
  • Anthropic Claude Code team member Thariq Shihipar gave a talk titled "A Field Guide to Fable" at the AI Engineer World's Fair, with a companion official blog post published the same day — reportedly racking up about two million reads within three days.
  • Core methodology: break down "what you know" into four quadrants — known knowns, known unknowns, unknown knowns, unknown unknowns. Reducing and pre-planning for these "unknowns" is the core skill for getting the most out of the new generation of models.
  • The talk lays out 8 ready-to-copy prompt patterns, organized by before, during, and after you start work, each with a ready-made example prompt.
  • A counterintuitive first-hand disclosure: Claude Code's system prompt was recently cut by 80% — for the new model, examples actually constrain it more than they help, and the direction has shifted from "giving constraints" to "giving context."
  • Thariq used this exact method to cut Fable's launch video from scratch — video editing was a completely unfamiliar domain for him.
⚑Stance flag: This is Anthropic's (Claude Code team's) own talk at the AI Engineer conference, plus a companion official blog post of the same title, about how to get the most out of their own Claude Fable 5 — vendor content. The talk contains almost no benchmarks, architecture, or hard numbers for Fable; it's mostly methodology and first-hand observations on internal prompt engineering.
1What This Talk Is About

What exactly is this talk about

Anthropic Claude Code team member Thariq Shihipar gave a keynote at the AI Engineer World's Fair, simultaneously publishing an official blog post of the same title, "A field guide to Claude Fable 5: Finding your unknowns."

This talk is about one very specific thing: how capable the Fable generation of models has become, the bottleneck has shifted away from the model itself and onto you — onto whether you can clearly articulate "what you don't know." The talk contains almost no hard numbers or architecture details for Fable; it's entirely about "how to collaborate with a more capable model."
📌
Why it's worth watching: Claude Code's system prompt was recently cut by 80%, shifting direction from "giving constraints" to "giving context" — a first-hand look at internal prompt-engineering changes at Anthropic. It also distills "how to get the most out of a more capable model" into 8 copy-paste-ready prompt patterns, each with a ready-made example.

One word keeps coming up in the talk: unhobbling. The idea is that what actually constrains a model is often the framework you've put on it yourself, and your old prompt-writing habits — frameworks that are essentially a reflection of how well you understand the model. Change them, and you can unlock capability the model already had.

An analogy

Take a horse that can already run, and remove the unnecessary reins and blinders.

~2 million
Reported read count for the companion official blog post within three days of publication
80%
The portion of Claude Code's system prompt recently trimmed, shifting from "giving constraints" to "giving context"
8
The number of copy-paste-ready prompt patterns the talk distills
Full talk · bilingual Chinese/English subtitles (about 19 minutes, click the cover to load) · Original video on YouTube (English) ↗
2Background · Prompts Doing Less

Models get smarter in "spikes" — prompts, meanwhile, need to do less

To understand why this generation of models needs "fewer examples, more context," look at two pieces of background first. This section is setup — the main point comes later.

The first piece of background is capability overhang: models don't get stronger evenly across the board — they suddenly leap ahead on certain specific tasks. There's a viral post online asking "why can't large models say which Pokémon names end in AW" — a regular chat model can't answer, even though it clearly knows all the Pokémon names. But Claude Code can answer, because it will fetch every Pokémon and write a script to filter for names ending in AW. Same "knowledge," but whether or not you give it a code-execution tool makes a world of difference in the result.

An analogy

Like ore veins buried at different depths underground — tools are the pickaxe that decides which vein you can reach. Half the work of using a new model well is figuring out what new possibilities actually exist now.

The second piece of background is more counterintuitive: system prompts are getting smaller. Thariq splits prompt-engineering best practice into three stages, and you can see the trend.

The Sonnet 3.5 New era
Small prompt · few tools
Relied mainly on piling on lots of examples to teach it what to do.
After models got stronger
Large prompt · many tools
You could pack in more information and instructions, and it started being able to execute them directly — examples kept piling up too.
The Fable generation
System prompt cut by 80%
Examples actually hold it back — it's more imaginative than the examples you give it. Give it context, not constraints; try not to write "don't do this."

Tools are also evolving alongside model capability. Take the ask-user-question tool (which lets the model pop multiple-choice questions back at you during planning) as an example: with Opus 4 it could barely call it; with Opus 4.5 you could tell it to "ask me 40 questions about the requirements" and it started being able to interview you; by Opus 4.8 and Fable, it can generate an entire HTML report with the questions embedded directly in it. Understanding a model is more like biology — very empirical, very organic — you need to build intuition for it.

3Core Framework

The core framework: sort your unknowns into four boxes

The plan in your head, the prompt, the spec — that's the "map." The real codebase and real-world constraints — that's the "territory." Every time Claude runs into something in the territory that isn't marked on the map, it has to guess what you actually want and make a call — that point is called an "unknown." The more work it does, the more unknowns it runs into.

Core Framework

In Thariq's own words: Fable is the first model that made him feel the bottleneck on output quality was whether he could clearly articulate its unknowns. And planning ahead alone isn't enough — unknowns can be buried deep in implementation and only surface later. So working with Fable is an iterative process of continually discovering unknowns before, during, and after you start work.

Facing a problem, break down "what you know" into four boxes.

Vertical axis: whether you're aware of it · Horizontal axis: whether you actually understand it
KNOWN KNOWN
Known Known
What you write into the prompt — explicitly telling it what you want.
KNOWN UNKNOWN
Known Unknown
Something you haven't figured out yet, but you know you haven't figured it out.
UNKNOWN KNOWN
Unknown Known
So obvious you'd never bother writing it down, but you know it when you see it.
UNKNOWN UNKNOWN
Unknown Unknown
Something you never even thought of — you don't know what knowledge you're missing, and you don't know how good something can actually be.

Top agentic coders (he named Boris and Jarred) share one thing in common: they have very few unknowns — watching them write prompts, you can tell they're completely on top of both the codebase and model behavior. At the same time, they assume unknowns will always exist. So reducing and pre-planning for your unknowns is the core skill of agentic coding as a craft — and it's a skill you can improve by practicing it with Claude.

Why is handling unknowns the key? Because instructing Claude is a delicate balance — being too specific and too vague both lose.

Instructions too specific
It will follow exactly what you said to the letter, even when a different direction would actually work better right now.
Instructions too vague
It fills in assumptions based on industry best practices on its own, which may not fit your task.

If you don't prepare for unknowns, you lose both ways: you don't know which stretch of road has pitfalls (not detailed enough where it needed to be), and you don't know which stretch is actually clear and could be left to run on its own (not let go where it could have been). The good news is Claude can help you find unknowns faster — it searches the codebase and the whole web extremely fast, and it iterates from failure faster than you do. The most critical step is giving it your "starting point": tell it what stage you're thinking at, how much experience you have with this problem and codebase, and let it be your thinking partner.

Below are 8 actionable patterns, organized into three stages: before, during, and after you start work. Each method card has a small four-quadrant icon in the top-right corner — the highlighted box is the type of unknown that pattern is primarily built to handle. Every example prompt is given in full: a paraphrase to help you understand it, plus the verbatim original text ready to copy and paste.

4Before You Start · Methods ①②

Two moves before you start: Blind Spot Pass + Brainstorms & Prototypes

Before you start, the two types of unknowns most worth resolving are: things you never even thought of (unknown unknowns), and things you can't put into words but recognize the moment you see them (unknown knowns).

①

Blind Spot PassFeatured in this piece

Handles "unknown unknowns." When you're writing a feature in an unfamiliar part of the codebase, or using Claude for work you're not familiar with (like design tuning), you likely have a pile of blind spots: not knowing what to ask, not knowing what "good" looks like, not knowing what pitfalls to avoid. Thariq says he literally uses the words "blind spot pass" and "unknown unknowns," and always gives it context on "who you are and what you already know."
Before adding a feature to an unfamiliar auth module, have it scan for your blind spots
"I'm working on adding a new auth provider but I know nothing about the auth modules in this codebase. Can you do a blind spot pass to help me figure out my relevant unknown unknowns and help me prompt you better."
Before doing work you don't understand at all (color grading), have it teach you to recognize your blind spots
"I don't know what color grading is but I need to grade this video. Can you teach me to understand my unknown unknowns about color grading, so that I can prompt better?"
②

Brainstorms & Prototypes

Handles "unknown knowns." In a domain where the standard is "you know it when you see it," have Claude brainstorm and build prototypes with you. Why do it early: discovering it only at the implementation stage is expensive — a small change to the spec can make the code implementation wildly different, and rolling back gets harder too. Visual design is the classic case — hard to describe in words, but you know instantly whether you want it or not.
When you have no visual taste, have it produce four wildly different directions for you to pick from
"I want a dashboard for this data but I have no visual taste and don't know what's possible. Make me an HTML page with 4 wildly different design directions so I can react to them."
Before touching real code, mock up a layout with fake data for you to react to
"Before wiring anything up, make a single HTML file mocking the new editor toolbar with fake data. I want to react to the layout before you touch the real app."
Give it a rough problem and have it search the codebase to brainstorm 10 angles
"Here's my rough problem: users churn after onboarding. Search the codebase and brainstorm 10 places we could intervene, from cheapest to most ambitious. I'll tell you which ones resonate."
5Before You Start · Methods ③④⑤

Three more moves before you start: let it interview you, give it references, ask for an implementation plan

Once you've brainstormed enough, there's usually still some unknowns left. The remaining three moves: force out the ambiguity, give it a better map, and have the plan put the "decisions most likely to change" up front.

③

Let the Model Interview You (Interviews)

Have Claude turn around and interview you, forcing out the ambiguity and unconsidered spots in your problem. Give it your problem's background to guide its questions during the interview.
Have it interview you to force out ambiguous spots
"Interview me one question at a time about anything ambiguous, prioritize questions where my answer would change the architecture."
④

References

Sometimes you can't clearly describe what you want — either you're short on words, or it's too complex to explain quickly. The best approach is to give it a reference. Images, documents, and screenshots all work, but the best reference is source code, even if it's written in a different language. Compared to a screenshot, source code gives it far richer detail about markup and structure.
Point it to a piece of reference source code, even if written in another language
"This Rust crate in vendor/rate-limiter implements the exact backoff behavior I want. Read it and reimplement the same semantics in our TypeScript API client."
⑤

Implementation Plans

Once you feel ready to start, have Claude produce an implementation plan for you to review first. The key is having it surface the things "you might actually want to change" up front, with mechanical refactoring pushed to the bottom.
Traditional implementation plan
Works its way down from mechanical details and file structure — the decisions you should really be deciding on get buried in the middle.
This approach
Leads with what you're most likely to want to adjust: data model changes, new type interfaces, anything user-facing; mechanical refactoring gets buried at the bottom.
Have it produce an implementation plan that leads with your most likely decisions
"Write an implementation plan in HTML, but lead with the decisions I'm most likely to tweak with: data model changes, new type interfaces, and anything user-facing. Bury the mechanical refactoring at the bottom, I trust you on that part."
6During and After · Methods ⑥⑦⑧

During and after: implementation notes, pitch docs, and letting it quiz you

Once you're happy with the plan, open a new session and feed in the artifacts — the spec, the prototypes — giving it a clean context window that still carries all the information from the planning stage. The next three moves cover the work in progress and after delivery.

⑥

Implementation Notes

Handles "unknown unknowns" that only surface deep in implementation. No matter how thorough the planning, the agent might hit some edge case in the code mid-work that forces a change of approach. Have it maintain a temporary implementation-notes.md, logging decisions along the way so you can learn from them next time.
Have it log decisions where it was forced to deviate from the plan, as it works
"Keep an implementation-notes.md file. If you hit an edge case that forces you to deviate from the plan, pick the conservative option, log it under 'Deviations', and keep going."
⑦

Pitches & Explainers

Delivering something has an important step: getting buy-in and approval. Use Claude to package the prototype, spec, and implementation notes into a "pitch and explainer" document — it speeds up understanding when the reviewer starts out with the same unknowns you had, and speeds up approval when experts want to see that you've considered the failure points they'd expect.
Package the prototype, spec, and implementation notes into a document for getting buy-in
"Package the prototype, the spec, and the implementation notes into a single doc I can drop in Slack to get buy-in. Lead with the demo GIF."
⑧

Quizzes

After a long session, Claude may have done far more than you realize. Looking at the code diff alone only gives you a shallow understanding, because a lot of behavior depends on existing code paths. Have it give you a bunch of context and then quiz you on it. Thariq says he only merges after acing the quiz himself.
Have it quiz you on the change — you have to pass every question
"I want to make sure I understand everything that's happened in this change. Give me a HTML report on the changes for me to read and understand with context, intuition, what was done, etc. and a quiz at the bottom on the changes that I must pass."
7Full Case Study

A living example: how he ran through this method himself

Fable's launch video was cut from start to finish by Thariq using Claude Code, and video editing was a completely new domain for him — he wasn't an expert. His approach happens to chain together all the methods above.

Known KnownKnew Claude could edit video with code and transcribe it, but wasn't sure the accuracy would be good enough.
→
Actively surfacing unknownsHad it explain how transcription tools like Whisper work, and whether ffmpeg could precisely cut out "um"s and long pauses.
→
Prototyping to test uncertaintyWanted a word-by-word synced subtitle UI, so had it build a prototype video with Remotion and the transcript to test it first.
→
Learn first, then actThe video looked washed out — a color grading issue — but he didn't know what "good grading" looked like, so he had Claude teach him and surface the unknowns first, then got to work.
Every explainer, brainstorm, interview, prototype, and reference is a cheap way to figure out what you didn't know before, before it gets expensive.Thariq Shihipar, A Field Guide to Fable
8Putting It Into Practice

A practical checklist: how to use this starting with your next project

The 8 patterns, grouped into a checklist by when to use them in your workflow — just match your situation to the list.

Before
  • ① Blind Spot PassWhen diving into an unfamiliar module or doing unfamiliar work
  • ② Brainstorms & PrototypesWhen the standard is "you know it when you see it"
  • ③ Let It Interview YouWhen ambiguity remains after brainstorming
  • ④ ReferencesWhen you can't put what you want into words
  • ⑤ Implementation PlanBefore starting, have it draft one for your review
During
  • ⑥ Implementation NotesWhen it's forced to deviate from the plan mid-work
After
  • ⑦ Pitches & ExplainersWhen you need buy-in or approval
  • ⑧ Let It Quiz YouBefore merging, force yourself to truly understand the change
Closing mindset · Dealing with loss

Thariq says the first time you use a model like Fable, the sense of gain and the sense of loss arrive together. He loves hand-writing code, loves the feeling of turning an entire codebase over in his head — but the only way through is through: stay in the loop, let the model run, and you'll come out the other side carrying more back with you.

Closing mindset · Be unreasonable

What he likes most about Anthropic is the belief that "tradeoffs" aren't really real. Force reality to lay its tradeoffs on the table: good, fast, cheap used to be pick-two — now you get all three. One last reminder: building has gotten easier, but creating value is still hard — don't pour all your energy into the build process and your setup.

Starting with your next project, let Claude help you find your unknowns first.
Source: Thariq Shihipar's keynote at the AI Engineer World's Fair, "A Field Guide to Fable," and the companion official blog post "A field guide to Claude Fable 5: Finding your unknowns" (claude.com/blog). This piece is a methodology breakdown; all example prompts are preserved in full as in the original — a paraphrase for readability, plus the verbatim original text ready to copy and paste. Figures cited in the piece (80%, ~2 million reads, etc.) are as stated in the talk and blog post.
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