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Part 01 / 05Block III · Inference

The model landscape

There is no such thing as "the LLM" - there are hundreds of models, in every size, open and closed. The good news: your harness stays the same. Only the number it dials changes.

Basics

Free for everyone: the concept, the analogy, the why.

In the LLM call we dialled a number: model. So far that field just held a name, and someone at the other end picked up. Now let's look at who you can actually call - because the choice is far bigger than the famous names suggest.

Two worlds: API and open weights

The first fork isn't "which model" but "where does it run". API models (Claude, GPT, Gemini) live with their provider: you send your request over, pay per token, and get the strongest model of the day without ever touching a graphics card. In exchange, your data leaves the house - and the provider can change prices, behaviour or the model itself at any time.

Open-weights models (Llama, Qwen, Mistral, Hermes …) can be downloaded - the weights, the actual numbers of the network, end up as a file on your disk. They run on your hardware, your data stays with you, and the model never changes without you. In exchange, you are now the operator.

By the way: "open weights" is not the same as "open source". You get the finished numbers, but rarely the training data or the recipe they were made with.

Size: what "7B" means

The B stands for billions - parameters, the learned numbers in the network. A 7B model has seven billion of them, a 70B model ten times as many. More parameters roughly means more world knowledge and better reasoning - but also more memory, more compute, more cost per answer.

Still, the reflex "take the biggest" is often wrong. For "summarise this email" or "is this answer a yes or a no?", a small model is faster, cheaper - and practically just as good. The skill is knowing your task, not the leaderboard.

Families and variants

Models come in families: same architecture, different sizes (Llama 3.1 ships as 8B, 70B and 405B). Within a family you'll meet suffixes:

  • Base - the raw model straight out of training. Completes text, but doesn't hold conversations.
  • Instruct / chat - post-trained to follow instructions. This is what you want for agents.
  • Specialists - for code, for images (vision), for embedding text (embeddings).

So which one do I take?

All of this clicks fastest when you see it on real models. That's what the panel below is for: not a ranking but a spectrum - from a 3B model for your notebook to the flagship that only runs in a data centre.

Browse

Twelve open models to look at

No ranking and no substitute for benchmarks - a shop window. Each tile shows this chapter's terms on a real model; one click opens the write-up and the way to the repo.

As of 2026-07-25 - every repo checked on that day. The model landscape ages fast: what you see here is a snapshot, not a leaderboard.

Size class
Built for
Architecture

12 models

Choosing a model is an engineering decision, not a religious war: task, budget and privacy decide who gets called - not this week's headline.

And your agent's architecture has priced that in from the start: model is a field in the request. The harness - conversation, role, tools, loop - stays exactly the same whether a 3B model on your laptop picks up or the biggest API model of the season.

Going deeper

With a free account: experiments, quizzes and the deeper material.

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Deep dive

For pro members: the depth for everyone who wants to actually build it.

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