I'm not sure to which extent this opinion is accurately informed. It is well known that nobody trains on 1M token-long content. It wouldn't work anyway as the dependencies are too far fetched and you end up with vanishing gradients.

RoPE (Rotary Positional Embeddings, think modulo or periodic arithmetics) scaling is key, whereby the model is trained on 16k tokens long content, and then scaled up to 100k+ [0]. Qwen 1M (who has near perfect recall over the complete window [1]) and Llama 4 10M pushed the limits of this technique, with Qwen reliably training with a much higher RoPE base, and Llama 4 coming up with iRoPE which claims scaling to extremely long contexts up to infinity.

[0]: https://arxiv.org/html/2310.05209v2

[1]: https://qwenlm.github.io/blog/qwen2.5-turbo/#passkey-retriev...