> For the complete documentation index, see [llms.txt](https://docs.commonstack.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.commonstack.ai/api-references/endpoint-specifications.md).

# Endpoint Specifications

This section covers endpoint specifications. Use whichever protocol fits your existing codebase, or mix both in the same project. 

For feature-specific usage (streaming, function calling, structured output, etc.), see the [User Guide](/user-guide/authentication.md). 

Commonstack exposes two sets of endpoints: an OpenAI-compatible API and an Anthropic-compatible API. Both accept the same API key and provide access to all models in the [Model Library](https://commonstack.ai/model-library). 

For Anthropic protocol usage, see [Anthropic SDK Compatibility](/user-guide/anthropic-sdk-compatibility.md).


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