By Sagar Shankaran, Founder of CallSphere
LLM tokens are the visible cost. The hidden 60-70% — evals, observability, guardrails, human review — is where TCO actually lives.
Key takeaways
Most 2026 agent budgets focus on LLM tokens because that is the line item with a real-time meter. The other costs are less visible but typically larger in aggregate. A working rule of thumb from operating CallSphere's six-product agent fleet:
This piece walks through the four hidden categories.
flowchart TB
Visible[Visible: LLM + voice tokens] --> Real[Hidden + Visible TCO]
H1[Eval framework] --> Real
H2[Observability + tracing] --> Real
H3[Guardrails + safety] --> Real
H4[Human review + QA] --> Real
H5[Platform + engineering] --> Real
H6[Incident response] --> Real
A real eval framework includes:
For a mid-sized agent, eval cost typically runs $10K-50K per month all-in.
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Tracing, metrics, dashboards, alerting, log retention. The 2026 stack:
Run-rate cost: $5K-30K per month for moderate volume; substantially higher at scale.
Input guards, output guards, rate limits, abuse detection, content moderation. Some are inline (latency-impacting); some are async (cost-impacting):
Typical run-rate: $2K-15K per month, scaling with volume.
The cost most underestimated. Even fully-automated agents need humans for:
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For a customer-service agent, 5-15 percent of conversations may touch a human at some point. At $30/hr loaded, even at the low end this is a substantial line item.
flowchart TB
M[Monthly cost example:<br/>500K calls/month] --> V[$45K LLM + voice]
M --> E[$25K Evals + observability]
M --> G[$8K Guardrails]
M --> H[$60K Human review]
M --> P[$20K Platform + engineering<br/>amortized]
Total[Total: $158K/month<br/>$0.32/call all-in]
V --> Total
E --> Total
G --> Total
H --> Total
P --> Total
The visible $45K is 28 percent of TCO. The other 72 percent is what production actually costs.
Three questions per category:
Some of these are setup costs (eval framework construction); some are perpetual (every-call inference). The mix matters for amortization. The 2026 reality: most enterprises in year 2 are paying more in ongoing operating costs than amortized setup.
The right TCO presentation shows all five categories, with monthly trend, broken into per-task unit economics. A single line item for "AI cost" hides where the money actually goes.
Written by
Sagar Shankaran· Founder, CallSphere
LinkedInSagar Shankaran is the founder of CallSphere, where he builds production AI voice and chat agents deployed across healthcare, hospitality, real estate, and home services. He writes about agentic AI, LLM engineering, and shipping voice agents that handle real calls in production.
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