I'm not super sure what I think of this project. I endorse the seed of the idea re "let's try to properly reverse engineer what representing facts in superposition looks like" and think this was a good idea ex ante. Ex post, I consider our results fairly negative, and have mostly confused that this kind of thing is cursed and we should pursue alternate approaches to interpretability (eg transcoders). I think this is a fairly useful insight! But also something I made from various other bits of data. Overall I think this was a fairly useful conclusion re updating away from ambitious mech interp and has had a positive impact on my future research, though it's harder to say if this impacted others (beyond the general sphere of people I mentor/manage)

I think the circuit analysis here is great, a decent case study of what high quality circuit analysis looks like, one of studies of factual recall I trust most (though I'm biased), and introduced some new tricks that I think are widely useful, like using probes to understand when information is introduced Vs signal boosted, and using mechanistic probes to interpret activations without needing training data. However, I largely haven't seen much work build on this, beyond a few scattered examples, which suggests it hasn't been too impactful. I also think this project took much longer than it should have, which is a bit sad.

Though, this did get discussed in a 3Blue1Brown video, which is the most important kind of impact!

I really like this paper (though, obviously, am extremely biased). I don't think it was groundbreaking, but I think it was an important contribution to mech interp, and one of my favourite papers that I've supervised.

Superposition seems like an important phenomena that affects our ability to understand language models. I think this paper was some of the first evidence that it actually happens in language models, and on what it actually looks like. Thinking about eg why neurons detecting compound words (eg blood pressure) were unusually easy to represent in superposition, while "this text is in French" merited dedicated neurons, helped significantly clarify my understanding of superposition beyond what was covered in Toy Models of Superposition (discussed in Appendix A). I also just like having case studies and examples of phenomena in language models to think about, and have found some of the neuron families in this paper helpful to keep in mind when reasoning about other weirdnesses in LLMs. I largely think the results in this paper have stood the test of time.

Sparse autoencoders have been one of the most important developments in mechanistic interpretability in the past year or so, and significantly shaped the research of the field (including my own work). I think this is in substantial part due to Towards Monosemanticity, between providing some rigorous preliminary evidence that the technique actually worked, a bunch of useful concepts like feature splitting, and practical advice for training these well. I think that understanding what concepts are represented in model activations is one of the most important problems in mech interp right now. Though highly imperfect, SAEs seem the best current bet we have here, and I expect whatever eventually works to look at least vaguely like an SAE.

I have various complaints and caveats about the paper (that I may elaborate on in a longer review in the discussion phase), and pessimisms about SAEs, but I think this work remains extremely impactful and significantly net positive on the field, and SAEs are a step in the right direction.

How would you evade their tools?

It's essentially training an SAE on the concatenation of the residual stream from the base model and the chat model. So, for each prompt, you run it through the base model to get a residual stream vector v_b, through the chat model to get a residual stream vector v_c, and then concatenate these to get a vector twice as long, and train an SAE on this (with some minor additional details that I'm not getting into)

This is somewhat similar to the approach of the ROME paper, which has been shown to not actually do fact editing, just inserting louder facts that drown out the old ones and maybe suppressing the old ones.

In general, the problem with optimising model behavior as a localisation technique is that you can't distinguish between something that truly edits the fact, and something which adds a new fact in another layer that cancels out the first fact and adds something new.

The high level claim seems pretty true to me. Come to the GDM alignment team, it's great over here! It seems quite important to me that all AGI labs have good safety teams

Thanks for writing the post!

Interesting thought! I expect there's systematic differences, though it's not quite obvious how. Your example seems pretty plausible to me. Meta SAEs are also more incentived to learn features which tend to split a lot, I think, as then they're useful for more predicting many latents. Though ones that don't split may be useful as they entirely explain a latent that's otherwise hard to explain.

Anyway, we haven't checked yet, but I expect many of the results in this post would look similar for eg sparse linear regression over a smaller SAEs decoder. Re why meta SAEs are interesting at all, they're much cheaper to train than a smaller SAE, and BatchTopK gives you more control over the L0 than you could easily get with sparse linear regression, which are some mild advantages, but you may have a small SAE lying around anyway. I see the interesting point of this post more as "SAE latents are not atomic, as shown by one method, but probably other methods would work well too"

but it's not clear to me that you couldn't train a smaller, somewhat-lossy meta-SAE even on an idealized SAE, so long as the data distribution had rare events or rare properties you could thow away cheaply.

IMO am "idealized" SAE just has no structure relating features, so nothing for a meta SAE to find. I'm not sure this is possible or desirable, to be clear! But I think that's what idealized units of analysis should look like

You could also play a similar game showing that latents in a larger SAE are "merely" compositions of latents in a smaller SAE.

I agree, we do this briefly later in the post, I believe. I see our contribution more as showing that this kind of thing is possible, than that meta SAEs are objectively the best tool for it

Ah, gotcha. Yes, agreed. Mech interp peer review is generally garbage and does a bad job of filtering for quality (though I think it was reasonable enough at the workshop!)