Prism serves its public models through the Anthropic Messages wire format. The
same model IDs and API keys work across the OpenAI and Anthropic formats.
Create a message
Body parameters
Put system instructions in the top-level system field. A message with
role: "system" inside messages returns 400.
Reasoning may produce thinking blocks before the final text block. Find the
text block by type instead of assuming content[0] contains the answer.
Count tokens
The token-counting endpoint accepts the input fields used to create a message
and returns the number of input tokens.
Authentication
The Anthropic headers are:
Authorization: Bearer YOUR_PRISM_API_KEY is also accepted.