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Course contents

  • Getting Started with AI for VLSI Engineers5
  • Just Enough AI: Models and Context15
  • Prompting13
  • Trust and Verification14
  • Using AI for Engineering Work17
  • Engineering Walkthroughs7
  • Practical Foundations for AI Workflows4
  • Engineering Data5
  • Retrieval-Augmented Generation6
  • Agents and Tool Use18
  • Agent Design8
  • MCP and Skills6
  • Multi-Agent Design6
  • Practical Capstone6
  • Tokens, Cost and Latency12
    • Cost Arithmetic
      • The Cost Formula
      • A Code-Review Job
      • A Nightly Regression Summary
      • Sensitivity and a Cost Calculator
    • Latency and Throughput
    • Reducing Tokens
  • Agentic Workflows for Chip Teams18
  • Interview and Judgment10
  • AI Skills: Full Course Index
  • Working with AI Glossary
  • Working with AI Cheatsheet
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‹Cost Arithmetic
  1. Topics
  2. AI Skills for VLSI Engineers
  3. Tokens, Cost and Latency
  4. Cost Arithmetic
  5. A Nightly Regression Summary

Reference: Tokens, Cost and Latency · Beginner to Intermediate

A Nightly Regression Summary

A worked nightly summary job cost with a 30-night monthly projection.

On this page

    A night as tokens

    Each night sends log excerpts plus short summarising instructions. It returns a compact report, so input again outweighs output.

    Output length varies by task and model. Budget from measured report sizes, not from hope.

    Period

    Nights

    Cost (units)

    Per night

    1

    0.204

    Per week

    7

    1.428

    Per 30 nights

    30

    6.12

    Cost per night

    One night carries 60000 input tokens and 2000 output tokens. The input part is 0.18 units and the output part is 0.024 units.

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    EXAMPLE prices (not real prices): 3 units per 1M input tokens, 12 units per 1M output tokens
    one night: 60000 input tokens, 2000 output tokens
    input part  = 60000 / 1000000 x 3 = 0.18 units
    output part = 2000 / 1000000 x 12 = 0.024 units
    per night   = 0.18 + 0.024 = 0.204 units
    input share  = 0.18 / 0.204 = 88.24%
    output share = 0.024 / 0.204 = 11.76%
    88.24 + 11.76 = 100.00

    Monthly projection

    Thirty identical nights cost 30 times one night: 6.12 units per month. That product is the monthly budget line.

    Halving the excerpt window to 30000 input tokens gives 0.09 plus 0.024, which is 0.114 units a night and 3.42 a month. The saving is 2.70 units a month against the same reports.

    Common pitfall

    Nightly logs grow without bound. Cap the excerpt window, or one bad night sets the whole monthly budget.

    Interview

    Likely probes: the monthly step and where the saving comes from.

    • Monthly cost is per-night cost times 30: 0.204 gives 6.12 units.

    • Input is 88.24% of the night, so trimming excerpts moves the total most.

    • Report length is the smaller lever here at 11.76% of the night.

    Check yourself One night costs 0.204 units. What do 7 nights and 30 nights cost?

    Seven nights cost 1.428 units. Thirty nights cost 6.12 units.

    Check yourself The excerpt window halves to 30000 input tokens with output unchanged. What is the new per-night cost?

    The input part halves to 0.09 units. The night costs 0.09 + 0.024 = 0.114 units.

    Related topics

    • A code-review job

    • Reducing tokens

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    See also

    • The Cost Formula