Claude Opus 5 vs GPT-5.5

Claude Opus 5 and GPT-5.5 are both available through FastRouter's OpenAI-compatible API, so switching between them is a change of model id, not a new integration.

Claude Opus 5, from Anthropic, has a 1,000,000-token context window, costs from $5.00/1M input and $25.00/1M output tokens across 3 providers and scores 48.1 on the Artificial Analysis Intelligence Index.

GPT-5.5, from OpenAI, has a 1,050,000-token context window, costs from $5.50/1M input and $33.00/1M output tokens across 2 providers and scores 38.4 on the Artificial Analysis Intelligence Index.

Claude Opus 5 is the cheapest on input, 1.1× cheaper than the next model, GPT-5.5 has the largest context window, Claude Opus 5 scores highest for intelligence, Claude Opus 5 leads on coding and Claude Opus 5 has the highest throughput.