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Johannes Weiss

@jweiss.io
689 followers 529 following 204 posts

Computer programmer (github.com/weissi). Distributed systems, ML infrastructure/eval, Swift, previously #SwiftNIO — ♥ snowboarding London, UK

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Johannes Weiss @jweiss.io · 2h
Might work?
Prompt: "can you stop sending me growth hack notifications like the above?"
Muse: "Done — the daily feature tour is off, so no more of those."
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Johannes Weiss @jweiss.io · 26/07/2026
Buying a #Deutschlandticket is the most German thing ever. You need a passport + selfie style ID verification to buy a _train ticket_. In Britain, I could get a mortgage with less scrutiny and hassle...
Identity check in progress
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Johannes Weiss @jweiss.io · 01/06/2026
Correct?
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Johannes Weiss @jweiss.io · 24/05/2026
Hmm, isaiprofitable.com is a bit odd. For Anthropic it shows $33B capex, $6.5B revenue which looks unprofitable. But their own sources say "Anthropic confirmed $30 billion in ARR, up from $9 billion at year-end 2025" (www.saastr.com/anthropic-ju...). So looks like they could break even if desired?
Anthropic $33B capex, $6.5B revenueAnthropic $30B ARR which appears to contradict the $6.5B cumulative revenue. Confused
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Johannes Weiss @jweiss.io · 31/12/2025
What should we call wholewheat (partially rye?) bread? I guess only Germans like that, so let's go with 'German bread' 😅. It's really yummy btw!
Wholewheat bread labelled 'German bread'
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Johannes Weiss @jweiss.io · 06/11/2025
Cat's marketing department is ... something. Seems like they're making gas turbines in a facility they call "Solar Turbines". Under the Oil & Gas category, of course.
In every region of the globe, Solar Turbines is a world leader in mid-range industrial gas turbines for use in power generation, natural gas compression, and pumping systems. Our systems last for decades, and so do our service and support.
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Johannes Weiss @jweiss.io · 06/10/2025
Isn't that too beautiful? PM2.5 of an overnight pyrolytic oven clean starting at 1am. Still woke up at 3am on account of bad air, despite closed doors and open windows in kitchen...
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Johannes Weiss @jweiss.io · 20/07/2025
The fun thing is that it actually gets most partial computations right but then in the last one it realises that it gave the wrong answer already. So it just halucinates "sin(0.8577)≈0.6365" (should be 0.7563) because it wants to be confident and justify the wrong answer it already gave.
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Johannes Weiss @jweiss.io · 28/05/2025
Heh, only realised today that a 'grape' and a 'grapefruit' are kinda confusingly named 🤓. On the first day I assumed somebody moved the sign, only on the second day I realised what likely's going on 💡
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Johannes Weiss @jweiss.io · 05/04/2025
Dad chores: alleviating lost Lego piece panic. How's your day going?
Lego set parts list next to handwritten inventory checklist.
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Johannes Weiss @jweiss.io · 29/03/2025
Glitch in the British Weather, it's not even April, it's stunning outside, I've had lunch outside twice this week and the next 10 days are ☀️. Kinda feeling guilty and anxious if there'll be any sun left for actual summer?!
Sunshine every day for the next 10 days in London
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Johannes Weiss @jweiss.io · 08/02/2025
Can't share the chat links because...
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Johannes Weiss @jweiss.io · 08/02/2025
At other times my 176 cells are only 64 though.
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Johannes Weiss @jweiss.io · 08/02/2025
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Johannes Weiss @jweiss.io · 08/02/2025
This is revealing: Asked o1 on chatgpt.com to "[...] please count all the cells. The ones with numbers and the ones without. Be super precise. Once you counted, count again and only reply if you're 100% sure" with this image. The image contains 8 x 22 =176 cells. o1 "counts" a whopping 2.4M cells.
A spreadsheet with 8 columns and 22 rows. The first row contains 1 through 8. The last row contains 2399993 through 2400000. All the other cells are empty.
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Johannes Weiss @jweiss.io · 01/02/2025
Haha, I appreciate the address :)
Cherry Capital Airport's address is 727 Fly Don’t Drive.
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Johannes Weiss @jweiss.io · 11/01/2025
Yes, Speedboat Bar is good!
Most outrageous value?Speedboat Bar, Soho.
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Johannes Weiss @jweiss.io · 11/01/2025
LOL, we do get a few people filming & photo shoots here but Insta Reels just had this in the bag for me: Uncle Roger being interviewed just beneath our flat. You don't see much of the surroundings and yet immediately knew "wait, that's here" www.instagram.com/reel/DCj3LJT...
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Johannes Weiss @jweiss.io · 01/01/2025
Evals really matter #
Anthropic’s Amanda Askell (responsible for much of the work behind Claude’s Character):

The boring yet crucial secret behind good system prompts is test-driven development. You don’t write down a system prompt and find ways to test it. You write down tests and find a system prompt that passes them.

It’s become abundantly clear over the course of 2024 that writing good automated evals for LLM-powered systems is the skill that’s most needed to build useful applications on top of these models. If you have a strong eval suite you can adopt new models faster, iterate better and build more reliable and useful product features than your competition.
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Johannes Weiss @jweiss.io · 01/01/2025
A drum l've been banging for a while is that LLMs are power-user tools - they're chainsaws disguised as kitchen knives. They look deceptively simple to use-how hard can it be to type messages to a chatbot? — but in reality you need a huge depth of both understanding and experience to make the most of them and avoid their many pitfalls.
If anything, this problem got worse in 2024.
We've built computer systems you can talk to in human language, that will answer your questions and usually get them right! ... depending on the question, and how you ask it, and whether it's accurately reflected in the undocumented and secret training set.
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Johannes Weiss @jweiss.io · 01/01/2025
An idea that surprisingly seems to have stuck in the public consciousness is that of "model collapse". This was first described in the paper The Curse of Recursion: Training on Generated Data Makes Models Forget in May 2023, and repeated in Nature in July 2024 with the more eye-catching headline Al models collapse when trained on recursively generated data.
The idea is seductive: as the internet floods with Al-generated slop the models themselves will degenerate, feeding on their own output in a way that leads to their inevitable demise!
That's clearly not happening. Instead, we are seeing Al labs increasingly train on synthetic content - deliberately creating artificial data to help steer their models in the right way.
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Johannes Weiss @jweiss.io · 01/01/2025
Is this infrastructure necessary? DeepSeek v3's $6m training cost and the continued crash in LLM prices might hint that it's not. But would you want to be the big tech executive that argued NOT to build out this infrastructure only to be proven wrong in a few years' time?
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Johannes Weiss @jweiss.io · 21/12/2024
Someone, somewhere: Got an idea: Let's create a tram line for people who don't actually have to go anywhere but just want a drink aboard Stuttgart, Germany: Fantastic idea, let's put a ln Xmas spin to it! Ladies and gents, meet the Mulled Wine Express.
Vintage tram that's now used to drink mulled wine.
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Johannes Weiss @jweiss.io · 14/12/2024
Ahh might be. It's Face -> Settings -> Calendar Sync
Flighty's Calendar Sync options
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Johannes Weiss @jweiss.io · 07/12/2024
Well actshualllly, Rimowa: hold my ... wine www.rimowa.com/gb/en/luggag...
Expensive Rimowa suitcase for 12 bottles of wine.
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Johannes Weiss @jweiss.io · 24/11/2024
Official now, the profile renamed to bsky.app/profile/lond... . It's the same DID as the old handle, see internect.info/did/did:plc:...
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Johannes Weiss @jweiss.io · 17/11/2024
286, 1 MB of RAM, 16 MHz, 40 MB C:, A: & B: floppy drives, MS-DOS 5.00. Compiling even a hello world in C took forever via MC1.EXE, MC2.EXE, LINK.EXE. Had more luck with QB.EXE Bootlegged copies of QuickBASIC and Microsoft C ofc, wayyy too expensive.
286 computer with MS-DOS 5.0.0
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Johannes Weiss @jweiss.io · 17/11/2024
Makes it look like this
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Johannes Weiss @jweiss.io · 17/11/2024
Very cool! FWIW, there's also Settings -> Thread Prefs -> Threaded Mode in the app
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Johannes Weiss @jweiss.io · 16/11/2024
What did I get up to on holiday you asked?
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Johannes Weiss @jweiss.io · 16/11/2024
Even the cheese shop wants me to get a subscription now... VC funded? jk 💀
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Johannes Weiss @jweiss.io · 13/11/2024
That is documented swiftinit.org/docs/swift/s...
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Johannes Weiss @jweiss.io · 19/08/2023
That's how we roll
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