Mercury 2.5 Preview and Muse Spark 1.1 are available through the OpenRouter API, so switching between them takes a model slug change rather than a new integration.
Mercury 2.5 Preview, from inception, has a 260,000-token context window and is priced at $0.04/M tokens input, $0.15/M tokens output on OpenRouter.
Muse Spark 1.1, from Meta, has a 1,048,576-token context window and is priced at $1.25/M tokens input, $4.25/M tokens output on OpenRouter.