Claude Opus 4.8 (Fast) and GPT-5.6 Terra are available through the OpenRouter API, so switching between them takes a model slug change rather than a new integration.
Claude Opus 4.8 (Fast), from Anthropic, has a 1,000,000-token context window and is priced at $10/M tokens input, $50/M tokens output on OpenRouter.
GPT-5.6 Terra, from OpenAI, has a 1,050,000-token context window and is priced at $2/M tokens input, $12/M tokens output on OpenRouter.