OpenAI vs Anthropic API for Production SaaS Features: A Technical Comparison

Short summary

A practical engineering comparison of OpenAI and Anthropic APIs focused on structural differences that matter in production: conversation state modeling, tool-calling protocols, caching, and rate-limiting. Argues that API contract design matters more than benchmark scores since models leapfrog each other every few months but API conventions persist longer. Covers OpenAI's flat message array vs newer Responses API and Anthropic's separate system-prompt approach.

• •API contract shape matters more than benchmark scores for production AI features
• •OpenAI uses flat message arrays (Chat Completions) or stateful Responses API; Anthropic separates system prompt from message array
• •Getting API design decisions right makes model swaps a config change; getting them wrong means rewriting orchestration layers

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