Slack AI agents are built on the core Slack application platform rather than an entirely isolated development system. Slack's agent documentation describes Slack as particularly suitable for agent experiences because it already provides a conversational environment, Block Kit interaction model, multiple application surfaces, identity, permissions, and contextual information. The official Agent quickstart demonstrates an agent using familiar Slack application mechanisms such as Bolt, App Home, modals, direct messages, app mentions, reactions, and threaded messaging. Developers can therefore combine AI reasoning and external model frameworks with established Slack primitives for events, messages, interfaces, authentication, and Web API actions. Agent functionality may introduce specialized capabilities and scopes, but it does not replace the underlying Slack platform. Agents can also post and stream responses. Consequently, B is the technically correct answer.