Ultrathink is a Claude Code magic word

https://simonwillison.net/2025/Apr/19/claude-code-best-practices/

by ghuntley • 1 year ago

113 39 1 year ago

simonwillison.net

andrewfromx• 1 year ago

I asked Claude if this was true, and Claude confirmed.

canadiantim• 1 year ago

That very very quickly moved from blog to twitter to blog to HN. Gotta love the velocity of information these days

doubled112• 1 year ago

Link first, ask questions later

sauravt• 1 year ago

megathink sounds better

benatkin• 1 year ago

And doublemegathink if you want it to do two megathinks in parallel

Terr_• 1 year ago

Not to be confused with doublethink, a mode that is always active for LLMs.

dghlsakjg• 1 year ago

But paradoxically only allocates 1/3 the tokens according to the code.

Perhaps they should switch to the metric thinking system.

Gigathinking, and Terathinking should be on the menu as well.

fragmede2• 1 year ago

Crazy that it's a key word that's implemented in the code that expands the context window, and that a light touch of reverse engineering was required to find it.

dickfickling• 1 year ago

It’s described here: https://www.anthropic.com/engineering/claude-code-best-pract...

fragmede2• 1 year ago

Ah yes, the documentation. If everyone read documentation, we wouldn't need LLMs to read it for us!

zenkey• 1 year ago

It would be cool if these "secret keywords" were more directly exposed in the UI somehow, perhaps as a toggleable developer/experimental mode? I would have a lot of fun tinkering with them.

refulgentis• 1 year ago

It's for Claude Code FWIW, just leaving a sigil here for fellow API implementers who are confused: your general point stands (though I wonder about UI affordances other than text given it's a CLI tool)

m1keil• 1 year ago

I hope we will exit this stage of magic spells and incantations sooner rather than later.

Frummy• 1 year ago

I hope we delve deeper into pentacles and rites in candlelit basements to appease black boxes of neural mimicries of canaanite archetypes

timschmidt• 1 year ago

So long as we get to play weird science[1] during the montage.

1: https://www.youtube.com/watch?v=Jm-upHSP9KU

patcon• 1 year ago

Sincerely, I respect your response to how arbitrary it seems in this form.

But... I'd like you to take a moment and think really hard about whether this is truly novel behavior for LLMs, or rather something that has always been part of the interplay between inter-agent communication and intra-agent thought :)

bee_rider• 1 year ago

It sounds like it is a “specific phrase mapped directly” based on another comment here? I guess that means hardcoded? Not completely sure, though.

4b11b4• 1 year ago

I thought that earlier on, I don't think we will though

ffsm8• 1 year ago

Maybe we will get to Babylon 5s reality of having literal tech wizards or whatever they were called - which summon "demons" etc

slowmovintarget• 1 year ago

Technomages. They were humans (and some others) bonded to Shadow-manipulated creatures that could affect spacetime. Technomages learned to "cast spells" in a private language they developed with their symbiote. These were essentially commands to "do the thing I'm talking about."

One of the challenges Technomages faced after acquiring their symbiote is gaining control over both the personal language and the impulses for destruction embedded by the Shadows (bias? bias).

So yes, learning the tricks of getting our AI agents to do the thing we actually meant, while aiming to overcome bias built in to the models when we can see it does sound an awful lot like Technomages dealing with their symbiote.

vunderba• 1 year ago

@dickfickling beat me to it, but ultrathink is already explicitly called out in the public Anthropic documentation:

"Ask Claude to make a plan for how to approach a specific problem. We recommend using the word "think" to trigger extended thinking mode, which gives Claude additional computation time to evaluate alternatives more thoroughly. These specific phrases are mapped directly to increasing levels of thinking budget in the system: "think" < "think hard" < "think harder" < "ultrathink." Each level allocates progressively more thinking budget for Claude to use."

https://www.anthropic.com/engineering/claude-code-best-pract...

I don't know what the max allowable "budget_tokens" is for Claude 3.7 Thinking mode, but the SDK shows an example of 32k which matches up with the article's findings.

simonw5• 1 year ago

Looks like that documentation is incorrect. It suggests there are four levels - "think" < "think hard" < "think harder" < "ultrathink." - but if you look in the code there are actually only three.

techjamie• 1 year ago

Pointed out elsewhere in this thread, but the docs call this phrase and others out as specific words to allocate a higher thinking budget.*

I'm assuming it's to unify the experience between chat and API, and avoid switching models for it ala OAI.

* https://www.anthropic.com/engineering/claude-code-best-pract...

wpollock• 1 year ago

Nice to know, although I was taught that the magic word is "please".

replwoacause• 1 year ago

This would be helpful information if I hadn’t already switched to Gemini 2.5 because it’s 96% cheaper

user3939382• 1 year ago

After stunts like Amp and Web Integrity (among others) I don’t care what they charge, I want nothing to do with Google.

arresin• 1 year ago

It does feel like a Faustian bargain using it.

esperent2• 1 year ago

I've had a frustrating time over the last couple of days with Gemini 2.5 Pro.

First I asked it to help me reverse the direction of text on a circle in Photoshop. It gave me very specific instructions which don't work and continued to argue with me that I was doing something wrong - I did my own research and found it's not actually possible to do this in Photoshop, and the instructions it was giving me were for Illustrator. 30 minutes of my time wasted.

This morning I asked it how to remove the axis lines from the orthographic view in Blender 4.3. I explained carefully that I know how to remove them in perspective view but that wasn't working for orthographic views. It over and over told me how to remove them from perspective views, telling me to use non existent UI elements, even drawing ASCII diagrams of how to find the nonexistent icons. When I said they didn't exist, it would circle back to telling me how to turn them off in the perspective view.

It turns out, again, it's not possible to remove grid lines from orthographic views in Blender (at least without messing around with the theme settings, or turning off the grid entirely).

In both cases it was incredibly persistent in stating the wrong way to do things, even when I was saying that it didn't work. I felt like it was gaslighting me, moreso than with any previous model I've used.

I haven't yet used it for writing code but these two experiences don't make me feel hopeful. The worst part about dealing with AI is when they are confidently incorrect.

simonw5• 1 year ago

These are good examples of things that I wouldn't expect an LLM to get right, based purely on my own intuition.

I don't believe they have much training material on the UI for tools at the moment - it may well come in the future as these new "computer use" models get fed vast amounts of screen capture videos, but to date my hunch is that there hasn't been much focus on that, especially for tools like Photoshop and Blender (training them to use a web browser is a whole lot more useful for the moment).

I'd encourage you not to assume they suck at code just because they suck at answering questions about Photoshop and Blender. I wrote about that a while back: "Don’t fall into the trap of anthropomorphizing LLMs and assuming that failures which would discredit a human should discredit the machine in the same way." - https://simonwillison.net/2025/Mar/11/using-llms-for-code/#s...

layer8• 1 year ago

I think I'll wait for Hyperthink.

namaria• 1 year ago

I'm personally holding out for Ludicrousthink

sn9• 1 year ago

Tengu think? As in Japanese Tengu?

xrd• 1 year ago

I'm scratching my head a bit at this one.

I already assume that the models are shifting underneath me. It's very frustrating that most non-developers just think you can ask an LLM a question and it will respond accurately each time. They are designed to make creative output and even if you dial down the temperature they still can hallucinate.

Why not be explicit about the thinking budget instead of aliasing it to a number with a term like ultrathink?

It's a cute word, and fun to know is managed on the client side, but isn't it again more imprecision to tools the are already suffering from that?

j_bum• 1 year ago

shifting underneath me

I love that language. This is something that’s constantly bothered me from the get go. Maybe I’m just wearing a tinfoil hat, but I swear I’ve noticed variations in behavior and performance within models across time.

This has been super annoying to me.

I always use the chat interfaces (mostly Claude atm), so I guess that just puts me at the whim of which sub-version of model Anthropic is serving for the day.

Or again, maybe I’m just hallucinating.

seanhunter• 1 year ago

It’s fair to point out this is probably already evidence for AGI. Most days I personally am only able to infrathink at best.

Ultrathink is a Claude Code magic word

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