Local LLMs for Coding: Context Is the Wall, Not the Model

You are probably not choosing the wrong model. You are running it with a sixteenth of the context it needs.

Ollama documents both halves and they collide. Its default context, by available VRAM:

• Under 24 GiB — 4k context
• 24–48 GiB — 32k
• 48 GiB or more — 256k

And its own guidance on what agentic work requires: tasks “which require large context like web search, agents, and coding tools should be set to at least 64000 tokens.”

So a machine with a 12GB or 16GB card — which is most people asking this question — starts at 4k against a documented requirement of 64k.

Why coding is different from chatting

A chat turn is short. An agent’s turn is not.

Point a coding tool at a repository and the context fills with the file it is editing, the files it opened to understand that one, the output of every command it ran, its own previous reasoning, and the instructions you gave it at the start. Then it does that again for the next step, carrying the lot.

4k tokens is a few hundred lines. The agent runs out of memory of the task before it finishes the task — which is experienced not as an error but as the model being stupid: forgetting the file it just edited, re-reading things, contradicting itself. The model was fine. It was working blindfolded.

The arithmetic that decides your machine

Weights first, because those are published. From Ollama’s library:

Model	Weights
qwen3:8b	5.2GB
qwen3:14b	9.3GB
qwen3-coder:30b	19GB
qwen3:32b	20GB
qwen3-coder:480b	290GB

Now put the good coding model on the card people aspire to. qwen3-coder:30b is 19GB of weights on a 24GB card — before a single token of context is allocated. Roughly 5GB left for the 64k the same vendor says the job needs.

Ollama’s warning is explicit: “Setting a larger context length will increase the amount of memory required to run a model. Ensure you have enough VRAM available.” How much more is not published per model, and we have not measured it — but the direction is not in dispute, and the headroom above is thin.

What that means at each tier

Read this as the shape of the constraint, not as a promise:

VRAM	Realistic for coding
8GB	An 8B model at small context. Fine for completion and single-file questions. Not an agent.
12–16GB	8B–14B comfortably, and the context becomes the thing you spend the headroom on rather than a bigger model.
24GB	A 30B coding model fits, and 64k context is tight against it. This is the first tier where agentic work is genuinely on the table.
48GB+	Ollama’s own defaults stop fighting you — 256k out of the box.

The unintuitive part, and the reason this article exists: between a bigger model and a bigger context, context is usually the better spend. A 14B model that can see the whole problem beats a 30B model that cannot.

What to actually do

• Raise the context before you change model. OLLAMA_CONTEXT_LENGTH=64000 ollama serve, then judge the same model again. This is free and it is the single change most likely to fix what you are experiencing.
• Then run ollama ps and read the PROCESSOR column. If raising context pushed part of the model into system RAM, you will see it there — and what the split means for speed covers why that matters more than it sounds.
• Prefer the smaller model with the larger window when you have to choose. For agents this is almost always the right trade.
• Do not buy a GPU on a model’s parameter count. Buy on total memory, then spend it deliberately between weights and context.
• Be honest about the tier you are in. At 8GB, local completion is good and local agentic coding is not there. Knowing that saves more time than any model download.