A new arXiv AI paper by Gabriele Bandini, Giulio Biroli, and Patrick Charbonneau, and 1 more studies Overcoming critical slowing down in frustrated spin systems by learned multiscale sampling.

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Simon Willison LLMs / 10:00 PM

Qwen 3.8 27B is excellent, but it defaults to wildly overthinking things

Friday's big release was Qwen 3.8 27B , an Apache 2 licensed 27B parameter vision-capable LLM from Alibaba's Qwen research lab. I've been looking forward to this one: 27B is an excellent size for running a model on a reasonably specced laptop, and its predecessor Qwen 3.6 27B was impressive. Qwen's self-reported benchmarks for this model are eye-opening. They show a boost from both Qwen 3.6 27B and the closed-weight Qwen 3.7-Plus, which was one of Qwen's strongest models of any size as recently as May this year . It will be interesting to hear what independent benchmarks have to say about the model. I've been running the model on two different machines: my 128GB M5 Max MacBook Pro, and an NVIDIA DGX Spark . On both machines I'm running LM Studio and their 17GB Q4_K_M quantized build . I also tried using llama-server directly on the Spark. The default of extra high results in spectacular over-thinking Qwen's documentation describes the model as defaulting to xhigh for the reasoning effort, and the LM Studio GGUF I've been trying preserves that default: Qwen3.8 comes with official support for reasoning_effort , which can be used to adjust reasoning depth and control cost: xhigh (default): for complex tasks demanding thorough analysis medium : balancing accuracy and speed low : efficient reasoning optimizing for speed and cost This is a hilarious default. It's absolutely not a good way to run the model, especially on consumer hardware. I've been finding the results extremely entertaining. I quickly ran into problems with LM Studio's default context limit of 8,192 tokens - Qwen was using them all up thinking about even the most mundane of problems. I loaded the model with the full 262,144 maximum context length and that problem went away. Here's the pelican riding a bicycle SVG I got from my first attempt with that increased context length. It took 21 minutes to generate, using 22,276 reasoning tokens to produce 3,223 tokens of output. You can read the reasoning trace here . This is by far the best pelican SVG I've been able to generate with a model that runs on a local machine - and this Qwen is pretty small, just a 17GB file on disk. There's a lot to like about this: The bicycle frame is the right shape It has legs on each side of the bike - that's very rare Good, clear pelican pouch The wings extend to touch the handlebars! The motion lines are behind, not in front It has a tasteful background - nice sun, clouds, hill, flowers and grass. Was that worth waiting 21 minutes for? Absolutely not. Here's that same prompt run with reasoning turned off - transcript here . This one produced 3,715 tokens and took 137s - just over two minutes. And just for completeness, I used OpenRouter to run the same prompt through the much larger Qwen 3.8 2.4T-A95B (released last week ) and got this snazzy animated SVG : Your browser does not support HTML5 video. I said Qwen at xhigh has a tendency to over-think things, but how bad really is it? I tried a much simpler prompt, again with that default extra high setting: draw an svg of a circle Qwen's reasoning trace started like this: The user is asking for an SVG drawing of a circle. Simple request — but I want it to be a carefully crafted piece. Let me make something that goes beyond just <circle> : a single self-contained SVG file with character — maybe a geometric "circle study," with subtle animation, layered rings, and a distinctive palette. Keep the scope right: they asked for an SVG of a circle. So the core is a circle. But I can add craft: concentric guide circles (like a compass/geometry drawing), tick marks, a soft gradient fill on the main circle, restrained ambient motion (a slowly rotating dashed ring, pulsing glow). Respect prefers-reduced-motion? That's more for CSS; SVG SMIL or CSS inside SVG will do. Palette options: deep teal ink on warm paper? Or bold vermilion circle on off-white with navy construction lines — Bauhaus/compass-drawing vibe. Let me go with a "geometric study" look: cool slate background, or bright paper white? Paper white is fine if it's not the cream-and-terracotta combo. [...] Several minutes later it produced this absolutely beautiful animated circle, which was entirely not what I had asked for! Your browser does not support HTML5 video. My strong recommendation: ignore that default. Run Qwen 3.8 27B on low or even no reasoning levels at first. It's a great model, but wow that default setting is a bad place to start. It's very good at bounding boxes A fun way to test a vision model is to see how well it can return bounding boxes around items in a photograph. I've seen previous Qwen models deal well with this, so I decided to put it to the test drawing bounding boxes around some pelicans. I've seen asking for 0-1000 scale produce good results in the past. I tried this: llm -a https://static.inaturalist.org/photos/714731804/large.jpg \ -m lmstudio/qwen/qwen3.8-27b \ ' Return JSON bounding boxes for the pelicans in this photo, 0-1000 scale for each dimension ' Here's the reasoning trace , which produced this: [ { "bbox_2d" : [ 195 , 290 , 370 , 780 ], "label" : " pelicans " }, { "bbox_2d" : [ 445 , 320 , 675 , 850 ], "label" : " pelicans " } ] This is such a good match . Here are those boxes rendered on top of the photo: Building a tool to label bounding boxes That visualization of the bounding boxes was taken using a new custom tool that I had Qwen 3.8 27B build for me, running offline on my laptop. I forgot to dial down the thinking effort so it was massively over-engineered , but it did manage to produce this full interface from this single prompt : [ {"bbox_2d": [195, 290, 370, 780], "label": "pelicans"}, {"bbox_2d": [445, 320, 675, 850], "label": "pelicans"} ] Build an HTML page which has an input box for accepting the URL to an image and a textarea for accepting the above style of JSON. It appends the image to the page, measures its width and height, then treats the coords in the bbox_2d as scaled from 0-1000 and scales them against the actual width and height, then it renders labelled boxes over the image. This screenshot shows one of the features I did not ask for - a demo scene, for if you don't have a photograph to test the tool with: Here's the relevant segment of the thinking trace, where it decided to draw its own pelicans purely because I had used the label "pelicans" in the example JSON I gave it in the prompt: Also a "load sample" that uses a known image? Can't depend on external images, but… the image URL input is user-provided; I could add a "try with sample" button [...] Hmm, I can draw a simple scene on canvas, export it as a data URL, and load it into the image — that's self-contained and demo-able! [...] But the user's coords are for an actual pelican image; a generated placeholder can still demo the scaling. Generate a 1000x1000 placeholder: gradient water + two blob-like "pelican" silhouettes placed at the given bboxes (using the same scale — cute: silhouettes at the exact 0-1000 positions, showing the boxes align). This makes for a fun, self-contained demo. Keep it simple: sky gradient, sun, water, two pelican-ish shapes (ellipse body, circle head, beak). Place at bbox centers. (I'm slightly nervous that models around the world might have a bias towards drawing pelicans at any chance they can get, brought on by nearly two years of exposure to my own stupid benchmark.) Is all that over-thinking necessary? Maybe it is, at least a bit. I tried with reasoning turned off and got this version , ( transcript here ), which nearly works but shows the boxes in the wrong place: So without reasoning it didn't quite one-shot a working tool. I'm sure it could get there with some follow-up prompts, but this is a good example of how reasoning can make a difference. Yes, it can drive coding agents One of the biggest questions around local models is whether or not they have enough horsepower to successfully run a coding agent loop. Coding agents require long context, strong code generation support and reliable tool-calling. On paper Qwen 3.8 27B has all three of these, so is it up to the task? My initial experiments with Pi have been very promising. I chose Pi because it has a shorter system prompt than most other options, making it a better fit for trying out smaller models. I configured Pi to use Qwen 3.8 27B running in LM Studio on the Spark (shared via tailscale serve ) by adding this to ~/.pi/agent/models.json : { "providers" : { "spark" : { "baseUrl" : " https://spark-18b3.tail68a31.ts.net/v1 " , "api" : " openai-responses " , "apiKey" : " dummy " , "models" : [ { "id" : " qwen3.8-27b " , "reasoning" : true } ] } } } Then ran pi --provider spark --model qwen3.8-27b in my ~/dev/datasette folder and prompted: how does auth work? After a sequence of reasoning and tool calls that accessed a bunch of different files it produced this reply , which is very solid. Just one problem: I wanted to share that transcript. So I pointed Pi and Qwen 3.8 27B at the JSONL transcript file in ~/.pi/agent/sessions/--Users-simon-Dropbox-dev-datasette-- and prompted: Write Python code to convert this jsonl to markdown And it built and tested this pi_jsonl_to_md.py , which did exactly what I needed. Here's that session transcript , published using the tool that it created. The quest for speed So far this is all looking very promising. We have a 17GB model that runs on high-end consumer hardware and can write code, drive tools, annotate images and generally do everything that I need from an LLM for getting real work done. There's one very significant catch: it feels slow - especially when it starts over-thinking, but even without that it's not particularly sprightly. I've been getting around 15-30 tokens a second from LM Studio. That's not terrible, but it's slow enough that it's going to be hard to win me away from hosted API models, which can return results a whole lot faster. Artificial Analysis track token speed and show OpenAI 5.6 Sol at 74 tokens/second and 5.6 Luna at an impressive 184/second. The good news is that the community have been exploring ways to speed things up since the model was first released two days ago. One of the most promising optimizations is baked into the model itself. Qwen supports Multi-Token Prediction , an architecture trick where a cheaper mechanism guesses several tokens ahead and the main model can then quickly verify if the guesses were correct. This can have quite a dramatic effect on inference performance. Based on this tweet from llama.cpp creator Georgi Gerganov I tried running the model with MTP like this on the Spark: llama serve \ -hf ggml-org/Qwen3.8-27B-GGUF:Q4_K_M \ -hfd ggml-org/Qwen3.8-27B-GGUF:Q4_0 \ --spec-default \ --spec-type draft-mtp \ --reasoning-preserve And sure enough, this gave me a significant boost. I had GPT-5.6 in Codex run a comparative benchmark on the Spark and the --spec-type draft-mtp server outperformed the LM Studio default GGUF by around 72%. I expect we'll see a whole lot more innovation around serving this model faster over the next few weeks. The MLX community likely have some tricks brewing as well. Some observations The fact that a 17GB file can do all of this stuff on my home machines is a miracle . Once again, I'm delighted and amazed at how much progress local models have made this year. A year ago this would have been competitive with the best and most expensive of the proprietary models - today it can run on a capable laptop. The only thing holding this back from being a daily driver is performance. It feels pretty slow on both the M5 Mac and the DGX Spark. That's the catch with these dense (non-Mixture-of-Experts) models - they require a whole lot of memory bandwidth to perform well, and neither of the machines I have access to are top performers in that regard. The most important thing about Qwen 3.8 27B is what it demonstrates . We can have an open weights general purpose model with a long context, effective tool calling, strong vision ability, and competent code generation, and we can fit the whole thing in just a 17GB file. The models at this size continue to get better at an impressive rate. We don't need to spend half a million dollars on datacenter-class hardware just to run a competent model. Tags: ai , generative-ai , local-llms , llms , qwen , pelican-riding-a-bicycle , llm-reasoning , llama-cpp , llm-release , coding-agents , lm-studio , ai-in-china , nvidia-spark , pi

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Simon Willison LLMs / 7:42 PM

One-shotting a Raccoon Heist game using Claude Fable 5

Back in 2022 I tweeted screenshots of a game concept generated by GPT-3 and some concept "art" created using DALL-E. Today, on the fourth anniversary of that tweet, I decided to see if Claude Fable 5 (running in Claude Code for web ) could build the entire game from the content of that tweet. It did a pretty good job of it! You can play the game here . Here's the GitHub repo , and a short video demo: Your browser does not support HTML5 video. How I built this This is the August 5th, 2022 tweet : My GPT-3 prompt back then was: Write a detailed product description of a computer game where a team of raccoons go on heists. This was in the text completion days, where you asked GPT-3 to complete the rest of the text. It completed: In "Raccoon Heist", you and your team of thieving raccoons are tasked with pulling off a series of daring heists. From robbing banks to stealing priceless art, no job is too big or too small for your furry crew. You'll need to use your wits and your skills to avoid the police and make a clean getaway with the loot. With exciting gameplay and a charming cast of characters, "Raccoon Heist" is the perfect game for anyone looking for a light-hearted caper. My prompt to DALL-E was short: Screenshot from a video game where a team of raccoons go on a heist Today's experiment: can I dump those screenshots into Fable 5 with a prompt telling it to write a game, then leave it to its own devices and get a working game at the end? Setting Claude Code for web up to use GitHub Pages A frustrating thing about Claude Code for web is that it can be hard to test what it's working on while it's still working. I've been using GitHub Pages to work around that limitation, and found it to work really well. Here's my process: Create a new repository for the project at https://github.com/new - this can be public or private, the trick works equally well for both. Start a Claude Code for web session, in the Claude iPhone or Desktop apps or in the browser at https://claude.ai/code Tell Claude what to work on, and encourage it to commit an index.html page as quickly as possible. This will create a branch with a name like claude/3d-raccoon-heist-game-50n293 Navigate to the Settings -> Pages area for the repository ( github.com/simonw/raccoon-heist/settings/pages in my case), select "Deploy from a branch", pick the branch name, and hit Save. That's all it takes! Within about 30 seconds of each push the latest content will be visible at yourname.github.io/your-repo/ . If you do this with a private repo, anyone who can guess the name of the repo will be able to view the published content. I don't worry much about this myself. The Fable 5 prompt Here's the prompt I gave Fable 5 (written in the notes app on my phone - this entire project was conducted on mobile). I accompanied it with the two images from the original tweet. Build this 3D game, for the browser. This repo is configured to serve static files so make sure there is an index.html that loads everything else. Make sure it is mobile-friendly (touch controls, works well on small screens). You have an OpenAI API key and access to their image generation model APIs, use that for textures to use with your 3D models. Docs here: https://developers.openai.com/api/docs/guides/image-generation - use gpt-image-2 Work independently - do not ask me to make any further design decisions. Make sure the game is fun, a little surprising, has good raccoon heist vibes, and is visually pleasing. Commit and push as often as possible so I can preview your work - start with an index.html that presents a title screen, then build from there. Append to a notes.md file as you work, including your changes to that as part of every commit. I didn't make any technology choices. I assumed (correctly) that it would probably use Three.js based on previous experiments. Giving Claude access to an OpenAI key turns out to work really well for filling in gaps in its capabilities - in this case we needed some way to generate images to use as textures. Fable is very good at prompting image generators! I said "Work independently - do not ask me to make any further design decisions" because I wanted to see if it could produce a full, working game without any further input from me. I also said "Commit and push as often as possible so I can preview your work". When you use Claude Code in the Claude iPhone app you give it a GitHub repository and it works in a branch. Telling it to "push as often as possible" means commits start landing in that branch straight away. I like asking for notes.md as a bit of added flavor - here's that finished file , and the entry it made when it added the dog: New escalation: from night 3 the yards get a patrolling guard dog — a low-poly brown hound with a spiked red collar and a wagging tail. It wanders between random spots, and within 12 units it catches your scent and tracks you by smell (line of sight is irrelevant — it's all nose, shown by a 👃 over its head and barking). It gives up if you open a 17-unit gap. Getting caught messages are now source-specific: guard / headlights / hound. Verified wander → track → caught with an automated test. Reviewing the transcript You can access the Claude Code shared session , and I also used my claude-code-transcripts tool to export my own HTML version which you can find here . Fable started with an index page, vendored a copy of Three.js, then wrote its own gen_textures.py script ( copy here ). It generated the textures and spot-checked them to make sure they looked OK. The metal.jpg file it generated for the trash can looks like this, though I don't think it was applied exactly right in the game itself: Then it built out the first basic version of the game, then decided to "smoke-test in the pre-installed Chromium" using Playwright. This meant it could take screenshots of its own work and eyeball them . It did that for both desktop and mobile widths of the page, then noticed that the raccoon was invisible at mobile widths, so it fixed that : The raccoon, dumpster hideout, and both crew raccoons are now perfectly visible on mobile. Committing this critical fix. It decided to generate a title screen, which it did using this gen_title.py script. Here's the gpt-image-2 prompt it used for that: Video game key art, low-poly 3D render style, moody nighttime scene: a cute low-poly raccoon wearing a tiny black burglar mask sneaking on its hind legs carrying a glowing gold coin, next to a tipped-over metal trash can, suburban house with warm glowing windows in the background, deep blue night, full moon, fireflies, cinematic rim lighting, charming heist caper mood. No text, no words, no logos. And the resulting image (which Claude thought was "gorgeous" ) - though I note that when it's shown on desktop it gets cropped to just the top third without the raccoon! Then my favorite change: it added the dog : export function makeDog ( ) { const g = new THREE . Group ( ) ; const BROWN = 0x8a6440 , DARK = 0x5e4128 ; const body = new THREE . Mesh ( new THREE . SphereGeometry ( 0.42 , 10 , 8 ) , M ( BROWN ) ) ; body . scale . set ( 0.9 , 0.8 , 1.5 ) ; body . position . y = 0.55 ; body . castShadow = true ; g . add ( body ) ; const head = new THREE . Mesh ( new THREE . SphereGeometry ( 0.3 , 10 , 8 ) , M ( BROWN ) ) ; head . position . set ( 0 , 0.85 , 0.62 ) ; g . add ( head ) ; const snout = new THREE . Mesh ( new THREE . SphereGeometry ( 0.16 , 8 , 6 ) , M ( DARK ) ) ; snout . scale . set ( 0.9 , 0.7 , 1.3 ) ; snout . position . set ( 0 , 0.76 , 0.9 ) ; g . add ( snout ) ; const nose = new THREE . Mesh ( new THREE . SphereGeometry ( 0.06 , 6 , 6 ) , M ( BLACK ) ) ; nose . position . set ( 0 , 0.78 , 1.08 ) ; g . add ( nose ) ; for ( const s of [ - 1 , 1 ] ) { const ear = new THREE . Mesh ( new THREE . SphereGeometry ( 0.12 , 6 , 6 ) , M ( DARK ) ) ; ear . scale . set ( 0.7 , 1.3 , 0.5 ) ; ear . position . set ( 0.2 * s , 1.08 , 0.55 ) ; g . add ( ear ) ; const eye = new THREE . Mesh ( new THREE . SphereGeometry ( 0.05 , 6 , 6 ) , M ( 0x1a1a1a , { emissive : 0x331111 } ) ) ; eye . position . set ( 0.13 * s , 0.92 , 0.86 ) ; g . add ( eye ) ; } const tail = new THREE . Mesh ( new THREE . CylinderGeometry ( 0.05 , 0.09 , 0.5 , 6 ) , M ( DARK ) ) ; tail . position . set ( 0 , 0.8 , - 0.62 ) ; tail . rotation . x = 0.8 ; g . add ( tail ) ; // spiked collar const collar = new THREE . Mesh ( new THREE . TorusGeometry ( 0.22 , 0.05 , 6 , 12 ) , M ( 0xc0392b ) ) ; collar . position . set ( 0 , 0.78 , 0.5 ) ; collar . rotation . x = Math . PI / 2.4 ; g . add ( collar ) ; const legGeo = new THREE . CylinderGeometry ( 0.07 , 0.09 , 0.34 , 6 ) ; const legs = [ ] ; for ( const [ x , z ] of [ [ - 0.22 , 0.35 ] , [ 0.22 , 0.35 ] , [ - 0.22 , - 0.35 ] , [ 0.22 , - 0.35 ] ] ) { const leg = new THREE . Mesh ( legGeo , M ( DARK ) ) ; leg . position . set ( x , 0.17 , z ) ; g . add ( leg ) ; legs . push ( leg ) ; } let phase = Math . random ( ) * 10 ; return { group : g , animate ( dt , speed ) { phase += dt * ( 3 + speed * 10 ) ; const amp = Math . min ( 0.6 , 0.1 + speed * 0.6 ) ; legs [ 0 ] . rotation . x = Math . sin ( phase ) * amp ; legs [ 3 ] . rotation . x = Math . sin ( phase ) * amp ; legs [ 1 ] . rotation . x = - Math . sin ( phase ) * amp ; legs [ 2 ] . rotation . x = - Math . sin ( phase ) * amp ; tail . rotation . z = Math . sin ( phase * 1.5 ) * 0.4 ; body . position . y = 0.55 + Math . abs ( Math . sin ( phase ) ) * 0.04 * ( 0.3 + speed ) ; } , } ; } And did a round of testing on it using Playwright, including another screenshot . // walk near the dog await page . evaluate ( ( ) => { const d = window . __rh . dog ; window . __rh . teleport ( d . x + 6 , d . z ) ; } ) ; await page . waitForTimeout ( 2000 ) ; info = await page . evaluate ( ( ) => JSON . stringify ( { dog : window . __rh . dog , state : window . __rh . state , player : window . __rh . debug ( ) . player } ) ) ; console . log ( 'after approach:' , info ) ; await page . waitForTimeout ( 3000 ) ; info = await page . evaluate ( ( ) => JSON . stringify ( { dog : window . __rh . dog , state : window . __rh . state } ) ) ; console . log ( 'after chase:' , info ) ; await page . screenshot ( { path : __dirname + '/shot-dog.png' } ) ; It made a few more tweaks, then declared itself done : Raccoon Heist is built, tested, and pushed — 7 commits on claude/3d-raccoon-heist-game-50n293 , all verified with automated Playwright playthroughs on desktop, portrait-phone, and landscape-phone viewports. The game: You're a masked raccoon sneaking out of your crew's dumpster hideout into a moonlit cul-de-sac. Grab coins, gems, rings, donuts, and fish (they visibly stack on your back and slow you down), then waddle home and bank them before dawn. Each night raises the goal and the heat: night 1 has one flashlight-sweeping guard, night 2 has two, night 3 adds a scent-tracking hound that ignores line-of-sight entirely. A police cruiser sweeps the street with headlights, homeowners randomly peek out of windows, a seagull periodically dive-bombs your unclaimed loot, pizza slices trigger a 6-second speed FRENZY, and a rare golden TV is worth 120 points if you can haul its weight home. Win ranks: TRASH PANDA ⭐ → CAT BURGLAR ⭐⭐ → MASTER OF DISGUISE ⭐⭐⭐, with your best run saved to localStorage. How it's built: Vendored Three.js (no CDN), procedural low-poly characters, and a procedural WebAudio soundtrack (sneaky walking-bass jazz plus all sound effects — zero audio files). All seven ground/wall textures and the title-screen hero art were generated with gpt-image-2 and committed as static assets, so the deployed game makes no API calls. Mobile gets a dynamic touch joystick (appears wherever you touch) plus a DASH button; desktop uses WASD/arrows and Space. Testing caught two real bugs worth mentioning: the canvas rendered at 2× size on any real phone (a cssText assignment was wiping Three.js's inline sizing — desktop DPR-1 tests masked it completely), and the win screen's star-rating div inherited the title screen's full-screen .stars CSS and silently swallowed every tap on the "next night" button. Both are fixed and regression-tested, along with pickup, banking, chase/caught, dawn, night progression, and lose/retry flows. notes.md has the full build log. The game is live on the branch — just serve the repo root and open index.html . Is the game any good? It's an impressive starting point, but it's not a good game. You move your raccoon around a yard collecting items - donuts, fish, gold coins, jewels - while avoiding guards with flashlights and, in later levels, a dog. You have a limited carrying capacity, and once that's full you need to drop stuff off at the dumpster. If you pick up a pizza slice you get a temporary speed boost. There are no team mechanics at all - there are two other static raccoons next to the dumpster but they're purely decoration. It gets slightly more challenging as the levels progress - the dog introduced in level 3 is the most interesting new mechanic - but it's very, very easy to beat. It's also pretty boring - each night has a fixed duration and you can collect all of the items and then have nothing else to do while waiting for the dawn. I was impressed by the implementation. It's fully 3D, there are trash cans, the flashlight illumination cones are fun, and it has a reasonably coherent visual style. It works on mobile. The music ("a procedural WebAudio soundtrack (sneaky walking-bass jazz plus all sound effects — zero audio files)" according to Claude) is simple but feels about right. As a finished game project, it's mediocre. As a starting point from a single prompt I think it's very impressive. I've vibe coded up quite a few games now. They've all been deeply disappointing from a gameplay perspective - it turns out designing games that are fun remains a uniquely human trait, and one which requires significantly more skill and experience than either Claude or I can bring to bear. That said, I thoroughly recommend tinkering with game development projects as a way to explore the capabilities of agents. It's a fun, low-risk way to try out new things. If you stick at it long enough you might even produce something that's worth playing! Update 7th August 2026 : I posed the same prompt to OpenAI Codex Desktop running GPT-5.6 Sol Ultra and got a significantly better result - GPT-5.6 Sol picked up on the importance of the squad of raccoons going on a heist, and built a game where you must rescue your two crewmates in a museum and then stack on top of them to steal the Golden Sardine. Tags: game-design , ai , prompt-engineering , generative-ai , llms , anthropic , claude , text-to-image , vibe-coding , coding-agents , claude-mythos-fable

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arXiv AI/ML / 5:16 PM

arXiv paper: Universal Thermodynamic Interatomic Potentials for Crystalline Materials

A new arXiv AI paper by Juno Nam, Bowen Deng, and Xiaochen Du, and 3 more studies Universal Thermodynamic Interatomic Potentials for Crystalline Materials.

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Simon Willison LLMs / 7:32 PM

sqlite-utils 4.0, now with database schema migrations

This morning I released sqlite-utils 4.0 , the 124th release of that project and the first major version bump since 3.0 in November 2020. In addition to some small but significant breaking changes (described in this upgrade guide ), this version introduces three major features: database migrations , nested transactions (via a new db.atomic() method), and support for compound foreign keys . Database schema migrations using sqlite-utils Schema migrations define a sequence of changes to be made to a SQLite database, plus a mechanism for tracking which migrations have been applied and applying any that are found to be pending. Migrations are defined in Python files using the sqlite-utils Python library , which includes a powerful table.transform() method providing enhanced alter table capabilities that are not supported by SQLite's ALTER TABLE statement. ( table.transform() implements the pattern recommended by the SQLite documentation - create a new temporary table with the new schema, copy across the data, then drop the old table and rename the temporary one in its place.) Here's an example migration file which creates a table called creatures , adds an additional column to it in a second step, then changes the types of two of the columns in a third: from sqlite_utils import Migrations migrations = Migrations ( "creatures" ) @ migrations () def create_table ( db ): db [ "creatures" ]. create ( { "id" : int , "name" : str , "species" : str }, pk = "id" , ) @ migrations () def add_weight ( db ): db [ "creatures" ]. add_column ( "weight" , float ) @ migrations () def change_column_types ( db ): db [ "creatures" ]. transform ( types = { "species" : int , "weight" : str }) Save that as migrations.py and run it against a fresh database like this: uvx sqlite-utils migrate data.db migrations.py Then if you check the schema of that database: uvx sqlite-utils schema data.db You'll see this SQL: CREATE TABLE " _sqlite_migrations " ( " id " INTEGER PRIMARY KEY , " migration_set " TEXT , " name " TEXT , " applied_at " TEXT ); CREATE UNIQUE INDEX " idx__sqlite_migrations_migration_set_name " ON " _sqlite_migrations " ( " migration_set " , " name " ); CREATE TABLE " creatures " ( " id " INTEGER PRIMARY KEY , " name " TEXT , " species " INTEGER , " weight " TEXT ); The _sqlite_migrations table is used to keep track of which migration functions have been run. The creatures table above is the schema after all three migrations have been applied. To see a list of migrations, both pending and applied, run this: uvx sqlite-utils migrate data.db migrations.py --list Output: Migrations for: creatures Applied: create_table - 2026-07-07 17:58:41.360051+00:00 add_weight - 2026-07-07 17:58:41.360608+00:00 change_column_types - 2026-07-07 18:01:15.802000+00:00 Pending: (none) If you don't specify a migrations file, the sqlite-utils migrate data.db command will scan the current directory and its subdirectories for files called migrations.py and apply any Migrations() instances it finds in them. You can also execute migrations from Python code using the migrations.apply(db) method, which is useful for building tools that manage their own database schemas over multiple versions. My own LLM tool has been using a version of this pattern for several years now, as shown in llm/embeddings_migrations.py . Prior art My favorite implementation of this pattern remains Django's Migrations , developed by Andrew Godwin based on his earlier project South . Fun fact: Andrew, Russ Keith-Magee, and I presented our competing approaches to schema migrations for Django on the Schema Evolution panel at the very first DjangoCon back in 2008! My attempt was called dmigrations , developed with a team at Global Radio in London. Django's migrations can be automatically generated from model definitions and include the ability to roll back to a previous version. The sqlite-utils approach is deliberately simpler: unlike Django, sqlite-utils encourages programmatic table creation rather than a model definition ORM, so there isn't anything we can use to automatically generate migrations. I decided to skip rollback, since in my experience it's a feature that is rarely used. With a SQLite project, an easy way to achieve rollback is to create a copy of your database file before you apply the migrations! Migrating from sqlite-migrate The design of sqlite-utils migrations is three years old now - I had originally released it as a separate package called sqlite-migrate , which never quite graduated beyond a beta release. I've used that package in enough places now that I'm confident in the design, so I've decided to promote it to a feature of sqlite-utils to make it available by default to all of the other tools in the growing sqlite-utils/Datasette/LLM ecosystem. I made one last release of sqlite-migrate , which switches it to depend on sqlite-utils>=4 and replaces the __init__.py file with the following: from sqlite_utils import Migrations __all__ = [ "Migrations" ] Any existing project that depends on sqlite-migrate should continue to work without alterations. Everything else in sqlite-utils 4.0 Here are the release notes for this version, with some inline annotations: The 4.0 release includes some minor backwards-incompatible fixes (hence the major version number bump) and introduces three major new features: Database migrations , providing a structured mechanism for evolving a project’s schema over time. ( #752 ) I think of migrations as the signature new feature, hence this blog post. Nested transaction support via db.atomic() , plus numerous improvements to how transactions work across the library. ( #755 ) sqlite-utils has long had a confused relationship with database transactions, partly because when I started designing the library back in 2018 I didn't yet have a great feel for how those worked in SQLite itself. Adding migrations to the core library made me determined to finally crack this nut, since transactions make migration systems a whole lot safer and easier to reason about. I ended up building this around a db.atomic() context manager which looks like this: with db . atomic (): db . table ( "dogs" ). insert ({ "id" : 1 , "name" : "Cleo" }, pk = "id" ) db . table ( "dogs" ). insert ({ "id" : 2 , "name" : "Pancakes" }) SQLite supports Savepoints , and as a result db.atomic() can be nested to carry out transactions inside of transactions. It's pretty neat! Support for compound foreign keys , including creation, transformation and introspection through table.foreign_keys . ( #594 ) This came about when I asked a coding agent to review all open issues and PRs for things that should be included in a 4.0 release since they would represent breaking changes if I added them later, and it correctly identified that compound foreign keys were exactly that kind of feature. I started with a breaking change to the table.foreign_keys introspection method, and then decided to see if Claude Fable 5 could handle the more fiddly job of integrating compound foreign key creation into the library. The API design it helped create felt exactly right to me - consistent with how the rest of the library worked already. Other notable changes include: Upserts now use SQLite’s INSERT ... ON CONFLICT ... DO UPDATE SET syntax, detect existing table primary keys automatically and reject records that are missing required primary key values. ( #652 ) This was the change that first pushed me to consider a breaking-change 4.0 version bump. I built this to help support sqlite-chronicle , which uses triggers to keep track of rows in a table that have been inserted, updated or deleted. db.query() now executes immediately and rejects statements that do not return rows; use db.execute() for writes and DDL. Probably the most disruptive breaking change - I've had to update a few places in my own code to switch from db.query() to db.execute() as a result. CSV and TSV imports now detect column types by default, while inserts into existing tables preserve those tables’ column types. ( #679 ) The sqlite-utils insert data.db creatures creatures.csv --detect-types flag was a later addition to allow column types (text, integer, real) to be automatically detected based on the data in a CSV. It should be the default, and releasing a 4.0 means I can make it so. table.extract() and extracts= no longer create lookup table records for all- null values. ( #186 ) The oldest issue addressed by this release - the underlying bug was opened (by me) in October 2020. See Upgrading from 3.x to 4.0 for details on backwards-incompatible changes. The detailed release notes for the features and fixes shipped during the 4.0 pre-release cycle are available in 4.0a0 , 4.0a1 , 4.0rc1 , 4.0rc2 , 4.0rc3 and 4.0rc4 . The upgrade guide was entirely written by Claude Fable 5, Claude Opus 4.8 and GPT-5.5. The same is true of the release notes. This is the kind of documentation I've slowly become comfortable outsourcing to the robots. It doesn't need to convince people of anything, or express any opinions - its job is to be as accurate and detailed as possible. I've reviewed the release notes closely and can confirm they are accurate and comprehensive. Claude Fable 5 helped a lot I released the first alpha of sqlite-utils 4.0 over a year ago . I've been dragging my heels on the stable release because of the amount of work it would take to track down and clean up the many other minor design flaws that a major version number allowed me to take on. Assistance from Claude Fable 5 (and to a lesser extent Opus 4.8 and GPT-5.5) gave me just the boost I needed to overcome inertia and make the most of the time I could afford to spend on this library. Fable has really good taste in API design, and is relentlessly proactive if you give it a more open goal. My most successful prompt was a review task that I issued against what I thought was the last release candidate: review the changes on main since the last tagged 3.x release - I am about to ship them as sqlite-utils 4.0, a stable version that promises no backwards-incompatible fixes for a very long time. review the changelog and upgrade guide, and write yourself scratch scripts to try out all of the new features in v4 - save those scripts but don't commit them I tried this with GPT-5.5 xhigh in Codex Desktop and Fable 5 in Claude Code. GPT-5.5 wrote 5 Python scripts and didn't turn up anything particularly interesting - its final report is here . Fable 5 wrote 12 scripts , identified 4 release blockers and 10 additional issues in its report , and built a neat combined repro script , which, when run, output the following: === 1. Failed db.execute() write leaves an implicit transaction open === in_transaction after failed write: True BUG: table 'other' silently lost when connection closed === 2. Leading ';' bypasses the query() first-token scanner === BUG: raised OperationalError: no such savepoint: sqlite_utils_query BUG: row persisted despite rollback (count=1) === 3. Rejected write PRAGMA via query() still takes effect === BUG: user_version=5 after 'rejected' statement (docs say no effect) === 4. Implicit compound FK resolves pk columns in table order, not PK order === BUG: other_columns reported as ('b', 'a'), should be ('a', 'b') BUG: transform of valid data raised IntegrityError: FOREIGN KEY constraint failed === 5. ForeignKey (now a dataclass) is no longer hashable === BUG: cannot use 'sqlite_utils.db.ForeignKey' as a set element (unhashable type: 'ForeignKey') === 6. Mixed ForeignKey objects and tuples in foreign_keys= rejected === BUG: foreign_keys= should be a list of tuples === 7. insert --csv into an EXISTING table transforms its column types === BUG: existing zip '01234' is now 1234 (column type: int) === 8. insert(pk=, alter=True) regression: InvalidColumns before alter runs === BUG: InvalidColumns: Invalid primary key column ['id'] for table t with columns ['a'] === 9. migrate --stop-before an already-applied migration applies everything === BUG: m2 was applied despite --stop-before m1 (m1 already applied) === 10. ensure_autocommit_on() silently commits an open transaction === BUG: row survived rollback (count=1) - transaction was committed I found myself agreeing with almost all of them. Here's the PR with 16 commits where we worked through them in turn. There's no doubt in my mind that sqlite-utils 4.0 is a significantly higher-quality release than if I had built it without the assistance of the latest frontier models. Tags: schema-migrations , projects , sqlite , ai , sqlite-utils , annotated-release-notes , generative-ai , llms , ai-assisted-programming , anthropic , claude , agentic-engineering , claude-mythos-fable

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