Catch expensive AI model usage in every pull request

When a developer adds a new gpt-4o call, nobody gets a notification. The cost lands silently in the monthly invoice. By then the pattern is set, the feature is shipped, and changing it means a refactor discussion nobody wants to have.

The PromptUnit AI Cost Analyzer posts a comment the moment a PR introduces expensive AI model usage, before the code merges.

What it detects

The action scans the added lines in every PR diff for references to:

• GPT-4o, GPT-4 Turbo, o1, o3
• Claude Opus
• Gemini 2.5 Pro

If it finds any of those models and PromptUnit is not already integrated, it posts a cost comparison comment on the PR. If PromptUnit is already in the diff, it stays quiet.

Setup

Create .github/workflows/ai-cost-analyzer.yml in your repository:

name: AI Cost Analyzer

on:
  pull_request:
    types: [opened, synchronize]

jobs:
  analyze:
    runs-on: ubuntu-latest
    permissions:
      pull-requests: write
    steps:
      - uses: promptunit/sdk@main
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}

That is the entire configuration. No API keys, no build step, no npm install. The action uses only Node.js built-in modules and the standard GITHUB_TOKEN that GitHub provides automatically to every workflow.

What the PR comment looks like

When expensive models are detected, the action posts a table showing what PromptUnit routing would cost compared to routing everything through the flagship model:

	Without routing	With PromptUnit
Simple tasks (classification, extraction, summarization)	Full model price	Up to 94% cheaper
Complex tasks (reasoning, code gen)	Full model price	Unchanged

It also shows the one-line SDK change that enables routing:

// Before
const openai = new OpenAI({ apiKey: process.env.OPENAI_API_KEY })

// After
import { createPromptUnit } from "@promptunit/sdk"
const openai = createPromptUnit({
  promptunitKey: process.env.PROMPTUNIT_API_KEY,
  openaiKey: process.env.OPENAI_API_KEY
})

If the developer pushes another commit, the action updates the existing comment rather than posting a duplicate.

Why at PR time

Code review is the cheapest moment to change a routing decision. Once the pattern is in production and copied across the codebase, it requires a deliberate effort to change. A PR comment costs nothing and takes ten seconds to read.

The action does not block merges, does not fail CI, and does not require any configuration on the developer's side. It is purely informational.

No build step

Most GitHub Actions that post useful PR comments depend on @actions/core and @actions/github, which require npm install at runtime or a pre-built dist file. The PromptUnit action uses only the Node.js built-in https module. There is nothing to install, nothing to cache, and no ncc build pipeline to maintain.

The action source is at github.com/promptunit/sdk under github-action/index.js.

14-day observation period

If a developer adds PromptUnit after seeing the PR comment, routing does not start immediately. PromptUnit runs in shadow mode for 14 days first: it logs every call, classifies each request, and projects your exact savings in the dashboard. No routing until you click Enable.

For teams already spending $3K or more per month on AI APIs, the observation period typically shows 40-70% reduction available. The action puts that number in front of the right person at the right time.

Start the free 14-day audit