Just yesterday I saw a talk from Spotify where they presented their own fast retrieval mechanism "Parallel Fusion Router" [1]. It's also in the "learned retrieval" paradigm - in their case they use a teacher LLM to train a much smaller router LLM how to retrieve, using an LLM-as-a-judge based reward function.

From my own experience, these learned methods from Apple, Spotify and others, are highly relevant to hyperscale only - when you are dealing with hundreds of millions of items to choose from (or more), and require super high relevance in the top-5. For all other use cases (up to a few million items) I found that just building a BM25 index, and giving the LLM a BM25 "search tool" and casting a "wide net" wins every single time compared to learned methods (though the latter are more publishable in recsys and icml).

[1] https://research.atspotify.com/2025/9/you-say-search-i-say-r...

I feel like retrieval approaches, despite how good your ranking mechanisms are, end up biasing LLMs into what a heuristics-based system with way worse understanding of the domain says. I guess is a trade off between speed and quality, but letting the LLM explore without a bias (based on my personal experience) seems to generally provide much better results in terms of quality for the final output.

Apple has a fascinating history of waiting and seeing how a market develops before entering with a better product and eventually dominating, the iPod and iPhone are two examples. It seems they may be building a strong position to pull that off again in the personal assistant AI category ChatGPT is trying to dominate.

I enjoy watching the slow burn approach Apple is deploying as they quietly gear up to offer some % of local inference on iPhones to provide most of the AI services consumers want. Local inference could enable a very low price point for AI services that Apple would leverage alongside their massive ecosystem advantages and privacy claims to compete very effectively for personal assistant AI subscriptions.

I'm not sold; that's not to say I can't be swayed, but I've spent a lot of time building RAG solutions as a "one-size-fits-all" against codebases and I am not convinced embedding models or any of the myriad BERT implementations work well enough that they can beat out grep.

Most embedding/BERT models are far too small to truly grasp the nettles when an AI ask questions to them; and if you condition the AI to only search for really basic things, then... you're basically back to grep + regex.

You need to prune all manner of useless detritus that might gum up your matches like test files, documentation, and sidecars that semantically overlap or you're just going to match your tests. That's fine if you're building a document store for a business, but if you want a "one-and-done" solution for your codebase it's rarely good enough.

And if you do use a very large embedding model (which means it'll require running in the cloud as most company computers won't run it well), then... well, you're better off just using a language model as a subagent to scout ahead for you and elide the embedding model to begin with.

as a recovering RAG-enthusiast, I will share a quote from a peer that has really stuck with me:

"why not use grep?"

Can't wait to see how they leverage this research to make Siri even worse!