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Machine Learning · head to head

OpenAI API vs Zoo

OpenAI API logo

OpenAI API

Machine Learning

Hosted API for OpenAI's language, embedding, image and audio models, billed per token

From
$0.15/per-million-tokens
Rated
-
Full reviewWebsite
Zoo logo

Zoo

CAD

Cloud CAD with a scripting language and a geometry engine exposed as an API

From
Free
Rated
-
Full reviewWebsite

The short version

  • Only Zoo has a free tier, so it costs nothing to try first.
  • Each has a real cost: OpenAI API cost scales with tokens rather than with seats, so a successful feature's bill grows with its adoption, and an interface that lets users paste long documents has no natural ceiling on spend unless you build one yourself.; Zoo the geometry engine runs entirely in Zoo's cloud and there is no offline mode, so an aircraft, a customer site with no guest wifi or an outage stops modelling work completely.
  • They diverge on capability: OpenAI API covers Text and reasoning models, Zoo covers KCL scripting.
  • Prices and features above were last checked on 31 August 2026.

Where they differ

Only the attributes on which OpenAI API and Zoo actually diverge.

Attributes where OpenAI API and Zoo differ
AttributeOpenAI APIZoo
Starting price$0.15/per-million-tokensFree
Pricing modelusage-basedPer user per month
Free tierNoYes
PlatformsApiWeb, Windows, macOS, Linux, API
CategoryMachine LearningCAD
Founded2015Unknown

Identical on both: user rating (Not yet rated).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in OpenAI API

  • Text and reasoning models
  • Embeddings
  • Speech and audio
  • Image generation
  • Function calling
  • Structured outputs
  • Batch processing
  • Prompt caching

Only in Zoo

  • KCL scripting
  • Design Studio
  • Design API
  • Zookeeper agent
  • Format conversion
  • Open source client

What people use each for

The jobs each tool is most often brought in to do.

OpenAI API

  • Adding summarisation, drafting or classification to an existing product where building a model would take longer than the product's whole roadmapnot Zoo
  • Retrieval-augmented question answering over internal documents, using the embedding and generation models togethernot Zoo
  • Extracting structured records from unstructured text, where schema-constrained output removes most of the parsing problemnot Zoo
  • Prototyping a language feature quickly to find out whether it is worth the cost of a self-hosted alternative laternot Zoo

Zoo

  • A hardware startup that wants part models reviewed in pull requests alongside firmwarenot OpenAI API
  • A software team generating thousands of parametric part variants programmatically rather than by handnot OpenAI API
  • A SaaS product that needs to render and convert customer CAD files without licensing a geometry kernelnot OpenAI API
  • An engineer who models occasional brackets and enclosures and does not want a four figure annual seatnot OpenAI API

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

OpenAI API

  • Cost scales with tokens rather than with seats, so a successful feature's bill grows with its adoption, and an interface that lets users paste long documents has no natural ceiling on spend unless you build one yourself.
  • Models are deprecated on the vendor's timetable, and a fine-tuned model built on a retired base goes with it, so the tuning work and the data curation behind it must be redone rather than migrated.
  • Behaviour shifts between model versions in ways no test catches unless you wrote one, so prompts tuned over months against a particular snapshot can regress quietly on migration, which makes an evaluation suite a prerequisite rather than an improvement.
  • It cannot run inside your own network, so data residency requirements, air-gapped environments and contracts forbidding third-party processing rule it out regardless of the provider's own security posture.
  • You inherit its availability and its rate limits, so a provider incident is an outage in your product and a traffic spike can be throttled at precisely the moment the feature is proving itself.

Zoo

  • The geometry engine runs entirely in Zoo's cloud and there is no offline mode, so an aircraft, a customer site with no guest wifi or an outage stops modelling work completely.
  • STEP and SLDPRT import are still labelled experimental, which means the most common way of receiving a supplier or customer model is the least reliable path into the tool.
  • Drawing production, GD&T and tolerance annotation are far behind SolidWorks, Creo and NX, so most users still need a second package to release a manufacturing drawing.
  • Zookeeper is billed in reasoning minutes rather than per seat, so a team cannot forecast next month's bill from headcount the way it can with conventional CAD subscriptions.
  • The open source label applies only to the Design Studio client; the kernel that does the modelling is closed and hosted, so forking the repository does not give you a product you can run yourself.

Pricing, plan by plan

OpenAI API

$0.15/per-million-tokens
  • GPT-4o mini$0.15/per-million-input-tokens
    • Fast
    • Affordable
  • GPT-4o$5/per-million-input-tokens
    • Multimodal
    • 128K context

Zoo

Free
  • FreeFree
    • Design Studio access
    • About 20 minutes of Zookeeper reasoning per month
    • Around $10 of API calls included
  • Plus$20/month
    • Roughly 400 Zookeeper minutes per month
    • Pay as you go beyond the allowance
    • Design Studio and API access
  • Pro$99/month
    • Unlimited Zookeeper reasoning
    • Higher API allowance
    • Priority support

Which should you pick?

Choose OpenAI API if

  • You need text and reasoning models.
  • You work on Api.
  • You also want embeddings.
OpenAI API review

Choose Zoo if

  • You need kcl scripting.
  • You want to start without paying.
  • You work on Web, Windows, macOS, Linux, API.
  • You also want design studio.
Zoo review

Questions people ask

Is OpenAI API or Zoo better?
Neither clearly leads. OpenAI API starts at $0.15/per-million-tokens and Zoo at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, OpenAI API or Zoo?
Zoo has a free tier; the other does not. Paid plans start at $0.15/per-million-tokens for OpenAI API and Free for Zoo.
Does OpenAI API or Zoo run on more platforms?
OpenAI API runs on Api. Zoo runs on Web, Windows, macOS, Linux, API.
Can I use Zoo for free?
Yes. Zoo has a free tier, so you can try it without paying. OpenAI API starts at $0.15/per-million-tokens.
What is OpenAI API best used for?
OpenAI API is most often used for adding summarisation, drafting or classification to an existing product where building a model would take longer than the product's whole roadmap, retrieval-augmented question answering over internal documents, using the embedding and generation models together, extracting structured records from unstructured text, where schema-constrained output removes most of the parsing problem, prototyping a language feature quickly to find out whether it is worth the cost of a self-hosted alternative later. Of those, adding summarisation, drafting or classification to an existing product where building a model would take longer than the product's whole roadmap and retrieval-augmented question answering over internal documents, using the embedding and generation models together are not what Zoo is typically brought in for.
What can OpenAI API do that Zoo cannot?
OpenAI API covers Text and reasoning models, Embeddings, Speech and audio, Image generation. Zoo covers KCL scripting, Design Studio, Design API, Zookeeper agent.

Answered from the vendors’ own pages

OpenAI API: Is my data used to train the models?

API inputs and outputs are not used for training by default, which differs from the consumer product. Retention periods and enterprise terms change, so read the current data usage policy rather than trusting a summary.

Zoo: Is Zoo the same company as KittyCAD?

Yes. KittyCAD renamed itself Zoo; the GitHub organisation is still KittyCAD and the scripting language KCL keeps the old initials.

OpenAI API: Can I run these models on my own hardware?

No. The weights are not distributed. If self-hosting is a requirement, you are looking at open-weight models instead, with the operational and quality trade-offs that implies.

Zoo: Can I use Zoo without an internet connection?

No. The geometry engine is a cloud service, so Design Studio needs a live connection to model anything.

OpenAI API: How is it priced?

Per token, with input and output priced differently and each model priced differently. Batch processing and cached input prefixes reduce it. The practical consequence is that your bill is a function of prompt design, not just of request count.

Zoo: Is Design Studio free?

There is a genuine free tier with a small monthly allowance of AI reasoning and API calls. Paid plans start at $20 per month.

OpenAI API: What is the difference from Azure OpenAI Service?

The same model family delivered by Microsoft under an Azure contract, with Azure identity, networking and regional controls, and a different release cadence for new models. Enterprises with an Azure agreement often choose it for procurement and data residency reasons rather than technical ones.

Zoo: Can I replace SolidWorks with Zoo?

Not for drawing release, large assemblies or GD&T. Teams typically use Zoo for programmatic part generation and keep an established package for production documentation.

OpenAI API: How do I keep the cost under control?

Cap input length, cache repeated prefixes, route easy requests to smaller models, use the batch path where latency does not matter, and set per-user limits before launch rather than after the first surprising invoice.

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