it’s been a dramatic couple of days, I didn’t expect the already clean essay to be read so widely. I've heard more interesting discussions about mechanistic interpretability – should we think mostly in features or mechanisms and the flow of data through them, how much do weak activations matter, how does scale change things, and lots of other questions – than I have in a long time and I’ve been happy to hear all the discussion! a couple things on the essay itself. it didn't have enough citations, only ones for the basic story, since it was an "informal research essay and working hypothesis" rather than a paper, and other prior work around neurons were in the technical paper we're still finishing up. but it blew up, so I've added citations to the essay as well. I also want to thank @curttigges who did a lot of the language neuron research with me finally, while there was quite a range of updates, from this being incremental and obvious to interpretability going from hopeless to fully solved, I want to try to be clear about roughly where I stand I used to think neural networks would take some big cleaning step and then we could begin the ordinary natural science of mapping the parts and how they connect, watching data flow through, mapping circuits, and so on. at various points, like late layers of early model organisms and most layers of language models years ago, this didn't really work. but now with better tools and better models of study, it works much better for smaller vision models, this normal science process worked surprisingly well, until the whole map started to be broadly filled in. For bigger modern language models, it seems promising so far, for both neurons and circuits, attribution graphs, basically everywhere we've glanced. the map isn't filling in, there's a lot of map. there's still off-target firing, neurons that do a few things, but so far it's not an incoherent mess that you can't explore and learn from, and over time we get better at learning how to see it. so maybe it keeps going, and mapping motifs and exploring actually gets you pretty far, maybe something like "all the way" to a reasonable solution. I don't think it would be so scientifically surprising if that were the case. everything in the neural network was built in some sense to be read – by its downstream readers – and if we can learn to look like a reader, we might find reading them relatively easy. many researchers I talk to outside interpretability assume the parts are already understandable, and the difficulty is just in the mapping stage! it was also my prior when I first started looking at neurons when I first joined the field. there's lots of highly interpretable ones, maybe that's just how neural networks are if you look right. even in the good world it would still take some iteration on tools, on ways of looking, neuron-attention interactions are tricky for instance. there's probably no bright red line separating "cleaning the model" from "learning to look better" but there's broad working principles, and as of now I think we should try to look relatively directly if we can it shouldn't be so hard to test, you can just start looking at things and iterating and trying to understand motifs and such and see if it just breaks down at some point. it can take some iteration, I would recommend a bias against assuming arbitrary mixtures when you don't understand something at first, but also explanations should be tested for now I'm pretty optimistic, and I'm glad there's excitement about interpretability, but too much can cause problems too. I think part might be that ai safety isn't a very hopeful field, and even moderate amounts of optimism about an important problem being solvable in the future fills a spot that has been malnourished for a while. across several safety disciplines, the researchers directly working on them are often more optimistic than the people broadcasting pessimism more broadly for neural network interpretability at least, these are extraordinarily experimentally accessible objects of science, I don't know of a better one, and we have automated scientists. we have many things going in our favor. it's important and it's fun. the circuitry of these machines can be beautiful, surprising, entertaining, and insightful. I've spent thousands of hours looking through them, asking questions and running experiments and testing things, and would do so even if it weren't so important. I think the problem is solvable, whether the simple thing works, it mostly works but we need some new things, or we need big new ideas. I think we can figure it out

interpretability might be the most important scientific problem in the world right now, as I don't think we can solve alignment if we don't know what we're building. I think I have good news about it. I co-authored early work in mechanistic interpretability at OpenAI and came away pessimistic, because neural networks appeared to fold into arbitrary tangled knots. years later, I started openai's first large-scale automated interpretability project, finding about 2% of neurons legible with the primitive tools we had with modern agentic tools and a much closer look, the picture looks totally different. the vast majority in models up to trillions of parameters are legible, and their circuits beautiful. many famous examples of tangled neurons turned out to be misunderstood. The roadblocks I expected mostly aren't there. I now think ambitious interpretability will be solved by the time we need it most, and possibly quite soon, as automated scientists keep improving. it may be a bitter lesson for interpretability: the simple thing, at absurd scale, works already-clean.goodfire.com/