Platform Cost Is Half the Bill
The LLM token line on an agentic deployment often equals or exceeds the platform list price. Forecast both.
The two lines
Worked example
Illustrative example, not a real company. 10,000 agent interactions per month, 12,000 tokens average per interaction at a 60/40 input/output mix on Claude Sonnet.
The token line is roughly $936 regardless of which platform you pick (the model does the work either way). The platform line varies by 1000x. This is the gap that procurement papers ignore.
The grounding line
Third line on a real bill
Beyond platform and token, grounded agents add a third line: search / retrieval calls. Vertex AI bills $14 per 1,000 grounded Google Search queries above 5,000 free per month from January 2026, plus $2.50 per 1,000 prompts for grounding with your own data via Vertex Search. Anthropic and OpenAI grounding via external retrieval is billed by the retrieval vendor (Tavily, Exa, Brave Search API).
How to forecast both lines
The platform line is your monthly subscription. The token line is your monthly electricity bill. Vendor pricing pages show you the rent; they do not show you the electricity. Forecast both.
Continue with Agent TCO for the full year-one cost stack.