Build vs Buy

The build vs buy is the cost equation — the managed APIs, the open-source stacks, or the in-house (L363) — the options (the buy: the managed L363 — the model L278, the vector DB L184; the open-source: the self-hosted L363 — the pgvector L183, the Langfuse L345; the build: the in-house L363 — the custom L363), the costs (the licensing L363, the maintenance L363, the team L363, the opportunity L363), and the decision (the core vs the context: the differentiator L363 built, the rest bought L363) — the enterprise's (L380) cost equation (L363).

The one-sentence interview answer: "The build vs buy is the cost equation (L363). The options (L363): the buy (L363) — the managed (L363): the model (L278), the vector DB (L184) — the license (L363) for the speed (L363); the open-source (L363) — the self-hosted (L363): the pgvector (L183), the Langfuse (L345) — the license-free (L363) for the ops (L363); and the build (L363) — the in-house (L363): the custom (L363) — the team (L363) for the control (L363). The costs (L363): the licensing (L363), the maintenance (L363) — the forever (L363), the team (L363) — the salaries (L363), and the opportunity (L363) — the core (L363) neglected (L363). The decision (L363): the core (L363) — the differentiator (L363): the unique (L363) workflow (L363) — built (L363); the context (L363) — the commodity (L363): the model (L278), the database (L268) — bought (L363). The AI's (L363): the model (L148) — the buy (L278); the RAG (L280) — the build or the managed (L280); the vector DB (L182) — the open-source (L183) or the managed (L184). The AI shape (L173): the enterprise (L380) — the model (L278) bought (L363), the RAG (L280) built (L363), the vector DB (L183) open-sourced (L363) — the cost equation (L363), decided (L363)."

Think of the build vs buy as the restaurant's kitchen decision. The restaurant (the enterprise, L380) decides what to cook in-house (the build, L363) and what to order (the buy, L363): the signature dish (the core, L363) — the secret recipe (the differentiator, L363) — cooked in-house (L363); the staples (the context, L363) — the bread (the model, L278), the dairy (the database, L268) — ordered (L363) or from the local mill (the open-source, L363). The costs (L363): the orders (the licensing, L363), the kitchen staff (the team, L363), and the ovens (the maintenance, L363). The restaurant works because the signature is in-house, and the staples are ordered (L363).

   the kitchen (the decision, L363)
   ┌────────────────────────────────────────────────────────┐
   │ the signature dish (the core, L363) — cooked in-house  │
   │ (L363)                                                 │
   │ the staples (the context, L363) — ordered (L363) or    │
   │ the local mill (the open-source, L363)                 │
   │ the costs (L363) — the orders, the staff, the ovens    │
   └────────────────────────────────────────────────────────┘

The mental model is the kitchen: the signature in-house, the staples ordered (L363).

   the component (L363)
        │  e.g. the RAG (L280)
        ▼
   ┌────────────────────── THE OPTIONS (L363) ──────────────────────────┐
   │  the buy (L363): the managed (L280) — the speed, the license      │
   │  the open-source (L363): the self-hosted (L363) — the free, the   │
   │  ops                                                              │
   │  the build (L363): the in-house (L363) — the control, the team    │
   └──────────────────────────┬───────────────────────────────────────┘
                              ▼
   ┌────────────────────── THE COSTS (L363) ────────────────────────────┐
   │  the licensing (L363) · the maintenance (L363) · the team (L363)  │
   └──────────────────────────┬───────────────────────────────────────┘
                              ▼
   ┌────────────────────── THE DECISION (L363) ─────────────────────────┐
   │  the core (L363)? → the build (L363)                              │
   │  the context (L363)? → the buy or the open-source (L363)          │
   └──────────────────────────────────────────────────────────────────┘

The flow is the decision: options → costs → core (L363).

• The options (L363). The buy (L363) — the managed; the open-source (L363) — the self-hosted; the build (L363) — the in-house.
• The costs (L363). The licensing (L363), the maintenance (L363), the team (L363), the opportunity (L363).
• The core (L363). The differentiator (L363) — built (L363); the context (L363) — the commodity (L363) — bought (L363).
• The AI's (L363). The model (L148) — the buy (L278); the RAG (L280) — the build or the managed (L280); the vector DB (L182) — the open-source (L183) or the managed (L184).

• An enterprise engagement (L379). The model (L278) bought, the RAG (L280) built — the equation (L363).
• A model decision (L148). The buy (L278) — the frontier (L148) via the API (L363).
• A vector DB decision (L182). The open-source (L183) vs the managed (L184) — the ops (L268) vs the license (L363).
• A RAG decision (L280). The build (L349) vs the managed (L280) — the core (L363).
• Anything enterprise (L380). The equation (L363) — the options, the costs, the core (L363).

The through-line: the equation is the decision's — the options, the costs, and the core (L363).

Say it in four moves:

1. The options. "The buy (L363), the open-source (L363), the build (L363)."
2. The costs. "The licensing, the maintenance, the team (L363)."
3. The core. "The differentiator — built; the commodity — bought (L363)."
4. The AI's. "The model (L278) bought, the RAG (L280) built, the vector DB (L183) open-sourced (L363)."

• The core is the test (L363). The differentiator (L363) built (L363); the context (L363) bought (L363) — the core (L363) only (L363).
• The maintenance is the hidden cost (L363). The build (L363) — the forever (L363): the bugs (L363), the upgrades (L363), the team (L363) — the L363 total (L363).
• The model is the buy (L363). The frontier (L148) — the API (L278) — the build (L363) of the model (L365) is the rare (L363) case (L363).
• The open-source is the middle (L363). The pgvector (L183) and the Langfuse (L345) — the free (L363) for the ops (L363) — the middle (L363) of the buy and the build (L363).
• The opportunity is the core's (L363). The team (L363) on the build (L363) — the core (L363) neglected (L363) — the opportunity cost (L363).

• The build-everything (L363). The model (L365) and the database (L268) built (L363) — the maintenance (L363) forever (L363) — the buy (L363) for the commodity (L363).
• The buy-everything (L363). The unique workflow (L363) outsourced (L363) — the differentiator (L363) lost (L363) — the build (L363) for the core (L363).
• The license-blind (L363). The managed (L363) at the scale (L358) — the cost (L368) explodes (L363) — the open-source (L363) considered (L363).
• The ops-blind (L363). The open-source (L183) self-hosted (L363) — the ops (L268) under-estimated (L363).
• The ADR-less (L361). The decision (L363) un-recorded (L361) — the defense (L363) lost (L361).

• Ask the core question (L363) — the differentiator (L363)?
• Build the core (L363) — the unique (L363) workflow (L363).
• Buy the commodity (L363) — the model (L278), the database (L268).
• Open-source the middle (L363) — the pgvector (L183), the Langfuse (L345).
• Record the ADR (L361) — the equation (L363), decided (L361).

Q: Walk me through the build vs buy.

A: The cost equation (L363). The options — the buy (the managed), the open-source (the self-hosted), the build (the in-house) (L363). The costs — the licensing, the maintenance, the team (L363). And the core — the differentiator built, the commodity bought (L363).

Q: How do you decide?

A: The core question (L363): is it the differentiator (L363) — the unique (L363) workflow (L363) — build (L363); is it the context (L363) — the commodity (L363): the model (L278), the database (L268) — buy (L363) or open-source (L363). The build (L363) is the maintenance's (L363) forever (L363) — the core (L363) only (L363).

Q: What's the AI's build vs buy?

A: The model (L148) — the buy (L278): the frontier (L148) via the API (L363); the RAG (L280) — the build (L349) if the retrieval (L189) is the differentiator (L363), the managed (L280) if not (L363); and the vector DB (L182) — the open-source (L183) for the ops (L268), the managed (L184) for the scale (L358).

Q: What's the hidden cost of the build?

A: The maintenance (L363): the build (L363) is the forever (L363) — the bugs (L363), the upgrades (L363), the team (L363) — plus the opportunity (L363): the team (L363) on the build (L363), the core (L363) neglected (L363). The equation (L363) includes the maintenance (L363).

• What are the options (L363)?
• How do you decide (L363)?
• What's the AI's build vs buy (L363)?
• What's the hidden cost of the build (L363)?
• What's the core (L363)?

The senior read: the core decides the column (L363).

// The build vs buy (L363) — the core question (L363).
// 1 · THE COMPONENTS (L363) — with the core test (L363).
const components = [
  {
    name: 'model',                          // the model (L148)
    core: false,                            // the commodity (L363)
    decision: 'buy',                        // the API (L278, L363)
    why: 'the frontier (L148) via the API (L363); the build (L365)
         is the rare case (L363)',
  },
  {
    name: 'rag-pipeline',                   // the RAG (L280)
    core: true,                             // the differentiator (L363)
    decision: 'build',                      // the custom retrieval (L349)
    why: 'the retrieval (L189) is the product (L363)',
  },
  {
    name: 'vector-db',                      // the vector store (L182)
    core: false,
    decision: 'open-source',                // the pgvector (L183)
    why: 'the free (L363) for the ops (L268) we already run (L363)',
  },
  {
    name: 'observability',                  // the L346 (L346)
    core: false,
    decision: 'open-source',                // the Langfuse (L345)
    why: 'the self-hosted (L345) keeps the data in our control (L363)',
  },
];

// 2 · THE COSTS (L363) — the total (L363).
//   the license (L363) vs the ops (L363) vs the team (L363)
//   the maintenance (L363) — the forever (L363)

// 3 · THE ADR (L361) — the equation, recorded (L361).

What the reader must SEE — the equation, applied:

  model: buy                → the commodity via the API (L278, L363)
  rag-pipeline: build       → the differentiator (L363)
  vector-db: open-source    → the free for the ops (L183, L363)
  observability: open-source → the data's control (L345, L363)
  the maintenance included  → the hidden cost (L363)

  The core built, the commodity bought, the middle open-sourced (L363).

• The buy is the speed (L363). The managed (L363) — the fastest (L363) to the market (L363).
• The open-source is the ops (L363). The self-hosted (L363) — the infra (L285) for the free (L363).
• The build is the team's (L363). The in-house (L363) — the salaries (L363) and the maintenance (L363).
• The decision is the cost's (L368). The equation (L363) — the L368 budget (L368) informed (L363).

• The build vs buy = the cost equation (L363): the options, the costs, the core.
• The options: the buy (L363), the open-source (L363), the build (L363).
• The costs: the licensing (L363), the maintenance (L363), the team (L363).
• The core: the differentiator — built; the commodity — bought (L363).
• The AI's: the model (L278) bought, the RAG (L280) built, the vector DB (L183) open-sourced (L363).

BUILD VS BUY = the cost equation

THE OPTIONS (L363)
  the buy (L363) — the managed: the model (L278), the vector DB (L184)
  the open-source (L363) — the self-hosted: the pgvector (L183),
    the Langfuse (L345)
  the build (L363) — the in-house: the custom (L363)

THE COSTS (L363)
  the licensing (L363) · the maintenance (L363) — the forever (L363)
  the team (L363) — the salaries (L363)
  the opportunity (L363) — the core (L363) neglected (L363)

THE CORE (L363)
  the differentiator (L363) — the unique (L363) workflow (L363)
    → the build (L363)
  the context (L363) — the commodity (L363): the model (L278),
    the database (L268) → the buy (L363)

THE AI'S (L363)
  the model (L148) → the buy (L278)
  the RAG (L280) → the build (L349) if the core (L363)
  the vector DB (L182) → the open-source (L183) or the managed (L184)

INTERVIEW, 4 MOVES
  1 options "the buy, the open-source, the build (L363)"
  2 costs   "the licensing, the maintenance, the team (L363)"
  3 core    "the differentiator built, the commodity bought (L363)"
  4 the AI's "the model bought, the RAG built, the DB open-sourced (L363)"

You now hold the equation: the options, the costs, and the core — with the signature in-house and the staples ordered. The restaurant's kitchen is decided — and the recipe is recorded (L363).

Next: evaluating the model and the platform vendors on the axes that matter — Vendor Selection (L364).