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Attention at Constant Cost per Token via Symmetry-Aware Taylor Approximation
- spacewhales 8mo agoGithub here: https://github.com/glassroom/sata_attention https://github.com/glassroom/sata_attention
- yanosh_kunsh 8mo agoSo does that mean that LLM inference could go down significantly in price and/or context length would dramatically increase?
- bluecoconut 8mo agoI almost feel like this goes opposite to what attention is good at. This would be good at approximating all the places where attention is low / not sharp. Where attention/the exponential is key is when it selects out / needle-in-haystack / winner-takes-all focus (the word "attention" itself sorta implies this), and this is where the taylor expression would fail to represent the values well. This just... softens attentions ability to attend? (I'm imagining that if in the context there's ~4-8 "similar" attention-targets that should be sharp, and regular attention learns to select the correct one, this taylor approximation version would wash out any difference and they'd all loosly be attended to, and it'd fail to isolate the correct signal) Really wish this had some downstream tests -- apply it to a pretrained model and see how performance degrades, train a fresh one, etc. The tests are worth doing, but I somehow don't feel that hopeful this is the unlock required for sub-quadratic attention. It's possible that a freshly trained model with this learns to attend without the sharp attention signals, but that seems a bit dubious to me. But also, maybe this combined with some other selective (sparse attention) trick, means that the hybrid model gets the "fuzzy long tail" of attention well represented as well as the sharpness well represented, and all together it could actually be a part of the larger solution.
- energy123 8mo ago> this is where the taylor expression would fail to represent the values well. "In practice, we find that four Taylor terms (P = 4) suffice for recovering conventional attention with elementwise errors of approximately the same magnitude as Float16 resolution"
- seanhunter 8mo agoI read that too, but I wondered whether elementwise error is the right metric. Surely the actual error metric should be to evaluate model performance for a conventional transformer model and then the same model with the attention mechanism replaced by this 4th order Taylor approximation?
- vlovich123 8mo agoBounded error weights by definition is a more strict evaluation criterion than “performance” metrics through running the model.
- ehsanu1 8mo agoTo spell it out for myself and others: approaching equivalent calculations for each individual attention block means we also approach equivalent performance for the combination of them. And with an error bar approaching floating point accuracy, the performance should be practically identical to regular attention. Elementwise errors of this magnitude can't lead to any noteworthy changes in the overall result, especially given how robust LLM networks seem to be to small deviations.
- mapontosevenths 8mo ago> This just... softens attentions ability to attend? I think this does soften, but not linearly. That is to say the fixed state size limitation means that it softens more as it gets further into the past.
- tehsauce 8mo agoRight, and when they compare to floating point accuracy they seem to be using the number of decimals supported by the mantissa, but the exponent is important no?
- seanhunter 8mo agoWhen someone says the error is of a certain magnitude they mean the absolute value of the difference between the the two things, so what they're saying is that the values they produced with their approximation are about as wrong as the difference between the actual values and those values cast to float16. The exponent is most definitely important and would be included in that.
- mapontosevenths 8mo agoThis uses the Taylor approximation to approximate softmax, but that IS only an approximation. I wonder exactly how much that trade-off costs in terms of accuracy vs performance? I note that they say it's close to float16 with four Taylor terms. My other concern would be that Taylor itself is fairly complex. I wonder how well GPU's handle this in comparison to good old fashioned softmax? The last time I used Taylor with a custom Triton kernel it was still very slow. That could just have been my own jank vibe-coded implementation though.
- slashdave 8mo agoIf the model learns by using the approximate softmax, then why does it matter? We only need the behavior of softmax, not an exact numerical solution.
- mapontosevenths 8mo agoI guess that what I'm saying is I'd love to see an LLM actually have it's attention mechanism replaced with this and get benchmarked on real world tasks in comparison to quadratic attention. They don't seem to have done that here. They claim that's it's close to being the same, but my experience tells me that it needs to do better than get "pretty close." They also haven't' tried to write a high performance kernel for triton yet. If it goes the way my last experiment with Taylor did they're in for some bad news. I'm just a hobbyist though, it's certainly possible that people with more time/resources could outperform me without much effort. I just want to see it tested on something familiar and benchmark-able.
- rvz 8mo ago> Our work enables unbounded token generation at modest fixed cost, substantially reducing the infrastructure and energy demands of large-scale Transformer models. The mathematical techniques we introduce are of independent interest. Now this is a very interesting paper, which hopefully should address the chronic inefficiencies of the AI lack of efficient methods and approaches in reducing their significant computational and energy demands which are off the charts. > These factors penalize performance relative to what a fused, hardware-optimized implementation could achieve, and the reported runtime results should therefore be interpreted conservatively. It's still early with several limitations, but the need for wasting billions on GPUs will begin to not make any sense soon.
- thomasahle 8mo agoThere's a graveyard of 100s of papers with "approximate near linear time attention." They always hope the speed increase makes up for the lower quality, but it never does. The quadratic time seems inherent to the problem. Indeed, there are lower bounds showing that sub n^2 algorithms can't work: https://arxiv.org/pdf/2302.13214 https://arxiv.org/pdf/2302.13214
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- cubefox 8mo agoI think DeepSeek V3.2 is sub n^2, but it clearly performs quite well, refuting the alleged lower bounds in the paper.
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- andy12_ 8mo agoIt really isn't sub N^2. The main attention is only O(Nk), but only thanks to a lightning indexer that still has complexity O(N^2). So overall it still has the same complexity; just with a smaller constant factor [1] > DSA reduces the core attention complexity of the main model from O(L^2) to O(Lk), where k (<< L) is the number of selected tokens. Although the lightning indexer still has a complexity of O(L^2), it requires much less computation compared with MLA in DeepSeek-V3.1-Terminus [1] https://arxiv.org/pdf/2512.02556 https://arxiv.org/pdf/2512.02556
- cubefox 8mo agoOkay, then let's see whether we are going to see real linear architectures, like Gated DeltaNet or Mamba-3, in some larger models. I don't believe there is a "lower bound" which states that those can never get to (or exceed) the real-world performance of quadratic attention. (Perfect recall in unrealistic needle-in-haystack tests doesn't count.)
- observationist 8mo agoThis could turbocharge ByT5 and other tokenless architectures, whose big downside was the increase in compute over longer sequences. It's easy to imagine a bunch of strategies with variable levels of "focus" and so on with a fixed compute budget assigned on the fly with learned optimizers informing the distribution.
- andes314 8mo agoLinear time attention doesn’t work, by principle. Dead end pursuit. Much great research on more efficient quadratic time inference
- smokel 8mo agoWhat about n log n?
- abeppu 8mo agoI haven't tried to follow the math closely but should there not be some concern about the region of convergence? It looks like they don't specifically discuss it. Or is there some reason this isn't a problem in this context?
- reactordev 8mo agoI fear they have completely overlooked it.
- measurablefunc 8mo agoThe Taylor series for the exponential is convergent everywhere so what radius of convergence are you talking about? All the functions they're approximating are convergent everywhere & you can easily prove that compositions of functions that are convergent everywhere are still convergent everywhere.
- alyxya 8mo agoThe best and proven linear attention is the Gated DeltaNet or variations of it, used by Kimi and Qwen. Anyone who thinks linear attention can't work is forgetting that models are a fixed size so attention should always be compressable to be linear. Another way to think of the feasibility of linear attention is that the standard attention mechanism can be made linear simply by removing the softmax so the kv cache stores the kv product as a constant size matrix instead. Softmax just normalizes attention, but it's not theoretically required.
- amluto 8mo agoI skimmed the paper, and I think I completely lost the plot. Sections 2.1 through 2.4 talk about the decomposing the per-token-pair attention (key vector from the ith token with query vector from the jth token, where, in inference, the jth token is the one being sampled) into an approximation that is only mildly outrageously exponential in size compared to the original exponential-of-a-dot product. And they get something that's a polynomial (in the mathematical sense -- you're literally evaluating a polynomial) and has a size that's manageable at 4th order. Okay, great, they took something simple and made it bigger and nastier but less transcendental without losing too much precision. (As far as I know, there is really nothing special about the exp in attention in the first place, so trying to approximate it well seems mostly useful insofar as it will keep existing models working.) But the reason that attention is quadratic is that each token gets evaluated with respect to each other token. They haven't changed this at all. Section 2.5 seems like it's deferring this to an appendix. Section 2.6 gives the hidden state size per token, which, on first read, is strictly larger than the hidden state in normal attention (in normal attention it's d_v * d_k -- I'm not sure where their +1 comes from). So what did the paper gain? Is there some detail that I missed or that the paper completely glossed over that explains why there is any gain of efficiency at all? For what it's worth, the paper's overall claim is, in some sense, impossible. You can think of attention as being a sort of vector database, and this gets more accurate the sharper you make the exponential. If you replace softmax with actual max, a query locates the key that is the closest match to the query and returns the associated value. This operation is a plain linear search, it's possible (in principle anyway) to do lots of queries and recover the entire contents of the database, and I think that any paper claiming to do it faster than linear time should explain how it's compressing the data and where the loss is. In language model terms, imagine an prompt like so: 1: [string 1] 2: [string 2] 3: [string 3] ... n: [string n] Tell me the string associated with the number k. As long as there's enough precision and enough query/key space to fit some embedding of the number k that will match the right thing (and there is a lot of room in high-dimensional spaces), one might expect a transformer to be able to answer this question. But this obviously requires memory with size linear in the prompt length. If you try to get rid of that, you necessarily lose something. (This is not to say that nice attention scaling is impossible -- one could imagine schemes where it takes the model multiple tokens to answer the question, and the number of tokens needed could scale, say, logarithmically with prompt size. But you still need that linear memory.)
- NedCode 8mo agoReference implementation: https://github.com/glassroom/sata_attention https://github.com/glassroom/sata_attention
- riemannzeta 8mo agoNeat result. The symmetry exploitation here reminds me of recent work connecting neural network training dynamics to renormalization group theory. Charles Martin's SETOL paper https://arxiv.org/abs/2507.17912 https://arxiv.org/abs/2507.17912 shows that well-trained layers converge to something like an RG fixed point—the eigenvalue spectrum of the weight matrix develops power-law tails with exponent α ≈ 2, which is the signature of scale invariance. At this fixed point, the "effective correlation space" is low-dimensional: you can truncate the SVD aggressively and recover nearly identical test accuracy. I wonder if there's a connection to your Taylor truncation order. In RG terms, higher-order polynomial interactions are "irrelevant operators"—they get suppressed as you flow toward the fixed point. If trained attention heads are sitting near this fixed point, that might explain why modest truncation orders work: the network has already learned to concentrate its computation in the lower-order terms. A testable prediction: layers with α closer to 2 (measurable via weightwatcher https://github.com/CalculatedContent/WeightWatcher https://github.com/CalculatedContent/WeightWatcher) might need fewer Taylor terms for accurate approximation than layers with α far from 2. If true, you could potentially use the spectral statistics to adaptively choose truncation order per-head.
- fheinsen 8mo agoYes, there must be a connection. While adaptive truncation may prove impractical, it should be possible to measure spectral statistics on sample data, and specify a different fixed truncation order per layer, per head, etc. The github repository lists many other possible improvements: https://github.com/glassroom/sata_attention#proof-of-concept https://github.com/glassroom/sata_attention#proof-of-concept
- charleshmartin 8mo agoRight. If the dynamics of training are governed by RG flow, then the best optimization path should remove redundant directions, as specified by the RG operator(s)
- physicsguy 8mo agoWith this, they've not provided an upper bound the error on the kernel expanded with N terms which I think is a big missing piece.
- Kubuxu 8mo agoA paper on the same topic: On the Expressiveness of Softmax Attention: A Recurrent Neural Network Perspective, Gabriel Mongaras, Eric C. Larson, https://arxiv.org/abs/2507.23632 https://arxiv.org/abs/2507.23632 Video presentation if someone prefers it: https://www.youtube.com/watch?v=PN3nYBowSvM https://www.youtube.com/watch?v=PN3nYBowSvM Linear attention is a first-degree approximation of Softmax attention, and model performance gets better as you increase the degree of the Taylor approximation. I'm thinking about adapting an existing model to Taylor-approximated attention. I think it should be possible with some model surgery and rehabilitation training.
- korbip 8mo agoThis was done already here as well: https://arxiv.org/abs/2507.04239 https://arxiv.org/abs/2507.04239
- cubefox 7mo agoSounds interesting, but... > these models dominate both exponential attention and linear attention at long-context training There is no exponential attention; standard attention is quadratic. Strange mistake.
- fheinsen 7mo agoThe github repository's first toy example is with 8 Taylor terms, applied to a context with 1B tokens, each token with 1K heads: https://github.com/glassroom/sata_attention https://github.com/glassroom/sata_attention That toy example is not practical with the quadratic formulation, because it would require computing and storing 1K attention matrices, each with 1B×1B dot-product scores. For example, at Float32 precision, those attention matrices would consume approximately 1K x 1B x 1B x 4 bytes = 3,725,290,298.5 Terabytes of memory, which is not practical. Like every other proposed method, this one must be tested too. If it performs well in practice, AI service providers who ignore it will find themselves at a disadvantage. Otherwise, the mathematical techniques introduced by this work are likely useful for other applications besides Transformer attention.