API costs of your agents

For those building/selling AI agents: how do you price API costs to clients? Curious how other builders here handle this. If you're selling agents (or agentic workflows) to clients, how do you deal with the underlying API costs (OpenAI, Anthropic, etc.)? A few things I'm trying to figure out: - Do you pass through the raw API cost 1:1, or mark it up? - Flat monthly fee regardless of usage, or usage-based billing? - If usage-based, how do you track/meter it per client? - Do you build in a margin for token cost volatility (models get cheaper/pricier over time)? - Any tools/stack you use to monitor spend per client in real time? Would love to hear how people are structuring this, especially for agents that make a lot of calls (multi-step workflows, RAG pipelines, etc.) where costs can swing a lot month to month. Thanks!