Claude Opus 4.6 (Fast) and Mistral Small 4 are available through the OpenRouter API, so switching between them takes a model slug change rather than a new integration.
Claude Opus 4.6 (Fast), from Anthropic, has a 1,000,000-token context window and is priced by the provider serving it on OpenRouter.
Mistral Small 4, from Mistral AI, has a 262,144-token context window and is priced at $0.15/M tokens input, $0.60/M tokens output on OpenRouter.