Menu
Concepts

Closed models

3 min readbeginnerUpdated 28 Sept 2026
1 · In one line

A fully closed model keeps its weights and code proprietary for internal use.

1 · What it is

Closed model access is a spectrum. Fully closed models are kept for internal use. Hosted applications let users interact through a specified interface, while APIs let software send requests programmatically.

OpenAI released GPT-4 through ChatGPT and an API, while its technical report omitted architecture, model-size, hardware and training-compute details. Stanford CRFM reports that GPT-4 weights are not made available.

Anthropic offers API access through Console accounts, and Google documents unary, streaming and real-time Gemini APIs.

2 · Why it exists

Model access and model artifact access are different.

Hosted useHosted access lets users interact only through a specified application or interface.
API useAPI access lets users send requests programmatically.
Limited detailThe GPT-4 report omits architecture, model size, hardware and training-compute details.
3 · How it works

Follow one request through a hosted model boundary.

GPT-4 weights are not made available.
  1. 1 · requestSend requests programmatically through an API.
  2. 2 · executeThe API processes the request.
  3. 3 · returnReceive the model output through the same interface.
  4. 4 · retainGPT-4 weights are not made available.

Model sharing options range from fully closed to fully open.

4 · Where it's used
WhoWhat they askWhat it works with
Application developer“Is this model available through an API or only a hosted app?”Provider access documentation
Security team“Where do prompts and model execution occur?”Service architecture and data-handling terms
Researcher“Which architecture and training details are disclosed?”Technical report and system card
5 · What it solves, and what it doesn't
solves
  • Hosted access lets users interact through a specified application or interface.
  • APIs can expose programmatic model access.
  • OpenAI released GPT-4 text input through ChatGPT and an API.
doesn't solve
  • GPT-4 weights are not made available.
  • A technical report may omit architecture or training details.
  • Hosted access limits users to a specific application or interface.
6 · Go deeper
Open-weight modelsWeightsModel servingInferenceFoundation models

Sources used

This explainer is written in original language. The links below support its factual claims.

  1. officialInternational AI Safety Report 2025, UK Government · read 28 Sept 2026
  2. paperGPT-4 Technical Report, OpenAI · read 28 Sept 2026
  3. officialGPT-4, OpenAI · read 28 Sept 2026
  4. officialHow can I access the Anthropic API?, Anthropic · read 28 Sept 2026
  5. docsGemini API reference, Google · read 28 Sept 2026
  6. articleOpenAI GPT-4 Foundation Model Transparency Index report, Stanford CRFM · read 28 Sept 2026
Suggest a correction