AI-ENGINEERING
    intermediate

    Model Selection

    AI Engineer path · lesson 92 of 124
    The idea
    Hiring, not shopping. You do not interview everyone who applied: you screen out whoever fails a hard requirement, shortlist on the CV, and then give the short list the same work sample. The CV is public evidence; the work sample is your eval; only one of them predicts the job.
    How to use
    Step the four funnel stages in order, then use the breakeven slider to find the request volume where self-hosting overtakes an API.
    Order matters. Each stage is more expensive than the one before it, so each one exists to make the next one cheaper.
    1. Hard gatesdozens → a handful2. Public evidencea handful → 3–43. Your own eval3–4 → 1–24. Cost, latency, risk1–2 → the choiceclick a stage
    1. Hard gates
    What disqualifies a model outright?
    Data residency and privacy terms, licence (is commercial use permitted? is the output restricted?), context length, modality, latency ceiling, whether it can be self-hosted at all. These are binary and they are not negotiable, so applying them first keeps you from evaluating models you were never allowed to use.
    The stage that gets skipped
    Stage 3 is the only one whose output transfers, and it is the one teams drop when they are in a hurry — because it requires an eval set, which requires deciding what good means. Every shortcut past it is paid back later as a production surprise that nobody can reproduce.

    Key insight

    Re-run the funnel, do not re-open the decision. When a new model lands, the shortlist stage is cheap and your eval set already exists — so the cost of re-checking is a few hours, and the cost of not re-checking is being one generation behind indefinitely.

    Narrow the field

    Sequence

    Order a model selection process from cheapest filter to most expensive.

    Tap a piece, then tap where it goes — or drag it. Tap the tray to take one back.

    1. 1Drop a step here
    2. 2Drop a step here
    3. 3Drop a step here
    4. 4Drop a step here
    5. 5Drop a step here
    5 pieces left to place

    Test your knowledge

    20 questions
    Question 1 of 20
    Score: 0

    The first stage of a model-selection funnel should be:

    The short version

    Hiring, not shopping. You do not interview everyone who applied: you screen out whoever fails a hard requirement, shortlist on the CV, and then give the short list the same work sample. The CV is public evidence; the work sample is your eval; only one of them predicts the job.

    In more depth

    Model Selection

    There are more usable models than any team can evaluate, and the set changes every few months. Run the decision as a funnel, cheapest filters first.

    The four stages

    1.Hard gates — data residency, licence, context length, modality, latency ceiling, self-hostability. Binary and non-negotiable. dozens → a handful
    2.Public evidence — benchmarks, leaderboards, model cards. Builds the shortlist; does not rank it. a handful → 3–4
    3.Your own eval — real prompts, your metrics, incumbent as baseline. The only stage whose result transfers. 3–4 → 1–2
    4.Cost, latency, risk — price at real token counts, p95 under load, rate limits, fallback. → the choice

    API vs open weights

    API wins on time-to-first-call, peak capability and zero ops. Open weights win on data residency, cost at very high volume, latency floor, finetuning freedom, version stability and vendor risk. The common end state is both, with a router in front.

    Reading a benchmark

    Benchmarks saturate, aggregate scores hide the shape, setups are rarely comparable, and contamination is hard to rule out. A 20-point gap between a public score and a fresh variant of the same test is the signature of memorisation. Treat every public number as an upper bound.

    Breakeven

    API = pure variable; self-host = mostly fixed. Two lines, one crossing. Utilisation is the variable nobody models: a GPU at 30% occupancy costs the same as one at 95%.

    Interview Questions

    Amazon
    Google
    Microsoft
    Meta
    OpenAI
    Anthropic
    Google
    Netflix
    Amazon
    Meta
    Microsoft
    OpenAI
    Amazon

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