Primer

Volume I · 05 · Retrieval

05 · The window

Retrieval

Weights are frozen. Facts that change, or that never fit in training, have to be fetched at request time and packed into context.

In English

The model’s weights are frozen at training time. They do not know your wiki, last week’s numbers, or a new API. Retrieval fetches relevant snippets at ask-time and pastes them into the window so the model can read them.

Try this
Type a question. See what the corpus returns. Toggle a snippet off and watch the answer lose that fact.
Keep this
Weights are memory of training. RAG is memory of now, stuffed into the prompt.

Lab · retrieve then generate

Top-k3
  1. c8 · Out of scope · stuffed99

    Northwind's Helsinki cafeteria is known for archipelago fish soup on Thursdays. This has no bearing on the robots.

  2. c1 · Company · stuffed57

    Northwind Robotics is a private company founded in 2019 in Helsinki. It builds warehouse cobots for cold-chain logistics.

  3. c6 · Funding · stuffed49

    Series B closed March 2026 at €84M, led by Atomico, valuing the company at €410M. Runway is 28 months.

  4. c5 · Leadership33

    CEO Aino Aalto previously led robotics at Valmet. CFO Markus Berg joined from Wärtsilä in 2023.

  5. c2 · Flagship product25

    The flagship cobot, Nimbus-4, ships with a 12 kg payload, 8-hour battery, and a pallet-face vision stack trained in-house.

  6. c4 · Safety25

    Nimbus-4 is ISO 10218-1 certified. Near humans it caps speed at 250 mm/s and requires a dual-channel e-stop.

  7. c7 · Software25

    Fleet software is a ROS 2 overlay called Gale. It schedules 40+ bots per site and exposes an MCP server for warehouse agents.

  8. c3 · Customers0

    Primary customers are Nordic grocers. A 2025 pilot with Kesko cut pick errors 31%. A UK trial with Tesco starts Q1 2027.

Assembled prompt

109 tokens stuffed · scores are lexical overlap, not embeddings

Use only the passages.

[c8] Northwind's Helsinki cafeteria is known for archipelago fish soup on Thursdays. This has no bearing on the robots.

[c1] Northwind Robotics is a private company founded in 2019 in Helsinki. It builds warehouse cobots for cold-chain logistics.

[c6] Series B closed March 2026 at €84M, led by Atomico, valuing the company at €410M. Runway is 28 months.

Question: Who is the CEO of Northwind?

Retrieval-augmented generation is a search step in front of the model. Chunk the corpus, rank, stuff the winners into the prompt, then generate. The model is still only predicting tokens — now over a prompt that happens to contain the facts you fetched.

Failure modes are ranking errors and context pollution, not “the model forgot.” If a bad chunk is in the window, it will be used. If a good one is not, it cannot be.