API compatibility - 0 documented limits
OpenAI (reference) API compatibility
OpenAI's own API at https://api.openai.com/v1 is the reference that OpenAI-compatible layers imitate. Its docs do not mention an Anthropic-compatible endpoint. The docs read list no specific limitations for either layer.
Verified against OpenAI's own documentation. Not documented means the docs read that day do not say; it never means No.
Compare every provider in the API compatibility matrix.
OpenAI-compatible API
Native APIhttps://api.openai.com/v1- Endpoints
- responses
- chat/completions
- embeddings
- models
- realtime
- Auth
- Authorization: Bearer OPENAI_API_KEY_OR_ACCESS_TOKEN (optional OpenAI-Organization and OpenAI-Project headers)
- Notes
- The reference API every other layer imitates; REST API version v1. OpenAI's reference steers new work to the Responses API. The SDKs default to this base URL, so no base_url is needed.
From the docs
curl https://api.openai.com/v1/models \ -H "Authorization: Bearer $OPENAI_API_KEY"
Anthropic-compatible API
Not documented- Notes
- The OpenAI API reference read today does not document an Anthropic-compatible endpoint.
Documented limitations
Parameters, content types and features OpenAI (reference)'s docs say its compatibility layers ignore, reject or change, each with the line it comes from. A layer with nothing listed may still differ in ways the docs do not spell out.
OpenAI-compatible layer0
No limitations listed in the docs read.
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