Seed 2.1 Turbo 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.
Seed 2.1 Turbo, from bytedance-seed, has a 262,144-token context window and is priced at $0.50/M tokens input, $2.50/M tokens output on OpenRouter.
GPT-5.6 Terra, from OpenAI, has a 1,050,000-token context window and is priced at $1/M tokens input, $6/M tokens output on OpenRouter.