This is a problem with long context models. To put it as simple and as bluntly as possible: just because they claim you can use 1M tokens in your context doesn't mean its true and you should do that.

Due to extreme quantization of models and the context's KV cache, and also just really shitty samplers provided to the user (hell, most are just getting rid of sampler knobs altogether), this problem will absolutely continue.

Want it to go away, almost like magic? Local inference. When its under your control, and no longer being forced to hold it wrong, all of the common LLM defects will go away.

> Want it to go away, almost like magic? Local inference. When its under your control, and no longer being forced to hold it wrong, all of the common LLM defects will go away.

This is just not true. Any local LLM you can host on consumer-accessible hardware has all of these defects, too. Adjusting the knobs doesn’t solve everything.

The closest you can get to frontier performance is Kimi K3, but you’re not hosting that unless your budget is on the order of a nice house in a good metro area.

I like my local LLMs as much as the next person and my office is currently uncomfortably warm from the amount of compute happening, but I would never agree that local LLMs solve all of the common LLM defects. This is peak wishful thinking.

In my experience, the local models and even the larger ones that we can’t run at home suffer more from long context degradation than the frontier models. You are exactly right that you need to manage context length, but even at fp16/bf16 the local models have a lower ceiling for usable context length in my experience.

How do they go away with local models? It's a bug of all LLMs not just cloud vs local. As mentioned in another comment, they did test local models here too and those failed as well.

At my org we've been building AI agents and one internal rule we have is to use at most 50% of the models context window with the recommendation to not go over 25% for large context window models.

Anytime I see a "1M Context Window", my brain always goes "Gotcha so a 250k usable window"

The needle benchmarks show, that models extended context works for the part, that can be explained as: "I can access/adress that part of the input".

I have no idea, why in that context, the number of attention heads isn't mentioned. Models have a limited set of them and obviously, a model can focus at N max things at a time, which has to put an upper bound of long context support in some way. There's just more things to lose focus to (or, mismanage the limited attention heads resources - per token)

One of my early experiments last year with open source models and context size was with GPT-OSS 20B (the mxfp4, the "smart" 4-bit quantization). Even though it boasted a 128k context size it was bad at recall around 32k characters (didn't bother to implement the tokenizer for counting).

The recall text was a simple hash generated, filler text from a dictionary file and a request at the end to return only the hash from the beginning of the prompt. Past 32k characters the response contained hallucinations of characters or full hashes.

Just having large context size doesn't paint a full picture of capabilities, prompt adherence and other quality metrics.

This is conspiratorial speculation though. They did test many open weights models which spanned the full spectrum of performance: Nemotron 3 Ultra second-worst, GLM 5.2 top five https://arxiv.org/html/2607.25398v1

I've noticed this trend of the sampler knobs being removed. Can you explain why this might be the case?

Would you mind sharing some of your setup? Which model and which params do you tweak (e.g. temperature)?

>Want it to go away, almost like magic? Local inference.

Ah yes, magic that costs the same as a new car.

Long-context models do work as advertised... just not when combined with multi-turn conversation sessions.

It's my understanding that, for all current models having long-context capability, the "parts" of the model that allow them to do long-context processing, are mostly-untouched descendants of academic model architectures; where these academic models were designed around a very constrained use-case assumption: that anyone using more than a "normal" amount of context would specifically be trying to apply a reasonably-sized prompt to an unreasonably-sized block of plain-old embedded data, as a single-shot conversation. (Consider a task like e.g. "summarize this entire book." Context = [prompt] + [text of book].) This is the use-case all these architectures were refined and benchmarked around. And even today, this is still basically the only way these models' long-context processing capabilities work.

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But I think it goes deeper than that. It's not just about how we've made long-context work so far. It's about what "attending to context" really means, and what that implies about what we'll ever expect a long-context model to be able to do.

I would describe long-context models as seeming to have two distinct types of "attention state" used when attending to the layer-1 input-vector / context window:

- They have some small amount (e.g. 8-32k) of regular "high-quality" attention state. This is likely inherited from the base model they are trained on top of.

- They also have a large amount of "low-quality" attention state. This is what the long-context training process has created.

The "high-quality attention state" isn't limited to referencing the first 8-32k of the context window, to be clear. The high-quality attention mechanism is just limited to "choosing" 8-32k of arbitrary data samples, each from its own arbitrary position in the context window, to form a bounded-sized vector upon which high-quality attention is then computed.

(You could think of this as the high-quality attention mechanism computing attention over the entire context, and then doing top-K sampling, i.e. zeroing out all but the K largest-valued elements of the resulting latent vector, where K=8-32k. That's not what it's actually doing—that'd require paying the very quadratic scaling cost that prevents us from just increasing the short-context window size—but it's a useful naive model for what it's doing.)

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It's harder to directly explain what the low-quality attention mechanism does, so let me try an analogy.

(While no one can yet give a definitive accounting of the abstract computational processes the matrix-multiply-ops against a given LLM's weights encode, we can still speak of possibility-spaces, or analogies via information/computability theory on what sorts of abstract operations the LLM "must" be performing to achieve the results it achieves. This is that kind of thing.)

Think of an LLM's evolved context-window attendance mechanisms as being somewhat akin to the LLM being a regular CPU program, that has access to a 1. block of raw addressable memory (i.e. the context itself), and 2. a block of pointers into that memory (i.e. the learned first-layer attention over the context.)

Our LLM program's logic, through mutations during training, gradually evolves into a form where it could be seen as implicitly declaring and using a growing set of variables: some bound to static addresses in the block of raw memory (i.e. static context-window positions), and others bound to static addresses in the block of pointers, where the raw-memory-address-value of the pointer (and thus what data from the context-window it will read as when "dereferenced") is the result of a dynamic calculation over one or more other variables (i.e. an arbitrary weighting of the layer-1 input vector, where the resulting vector element is used as a selector, in layer 2, among other data that got sampled into "passthrough" vector-elements back in layer 1.)

Under this analogy, a model's "high-quality attention state" is the set of "named" pointer variables that it directly references in its logic.

As should be obvious, there can only be so many of these; you really fundamentally can't scale them up, without literally having "more logic" that defines and makes use of them (i.e. scaling up the size-in-weights of the model's layers.)

A model's "low-quality attention state", on the other hand, is the block of pointer memory itself, which can be as large as you like. Presuming the computational substrate permits the logic to compute on the addresses of memory within that pointer-memory block and then double-dereference them to get context data (and it does seem to!), your LLM's evolved logic can do "dynamic random-access reads" of arbitrary parts of the long context.

But, of course, the model won't be doing anything special with that data. It can attend to it, but not in a way that's unique to that data. It pulled in such data through generic logic that doesn't "know what it's looking at", after all.

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IMHO, this analogy helps to make clear that while giving a model a raw "large-context capability" might help said model to attend to more data, it doesn't really help in making a model able to attend to a larger prompt.

Just by information theory, an instruction-following capability must imply that something analogous to logic keyed on those instructions gets embedded into the weights; and that logic, in order to activate and work, presumably requires its own state — i.e. requires that individual values from the context are getting attended into additional top-level named variables.

And while the short-context attendance mechanism does that, the long-context attendance mechanism inherently does not / cannot.

And this means that there is likely a practical upper limit (in terms of practical model-weight size + latent-vector size + etc) to "how much prompt" a model can follow during a single inference step. Regardless of how much data the model can "see" on a given inference step, its active "program logic" is only defined in terms of so many concurrent stateful computations.

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Thus: trying to use a current long-context model's "low quality" attention to attend to a large prompt is just going to result in nonsense. None of these model families have ever been trained to follow a million sentences of rules simultaneously when answering a question. They're just going to attend with their inherited bounded "high quality" attention to your prompt as best as they're able, while forgetting literally everything about the prompt that doesn't fit in that bounded "high quality" window.

And anything that allows current long-context models to appear to interact well in multi-turn conversations with memory + KV caching + etc layers in operation — while also making use of its "low quality" attention to attend to large data — is some kind of hack, and will break like a hack.