AssemblyAI Cost Tuning

Overview

Optimize AssemblyAI costs through model selection, feature-aware billing, and usage monitoring. AssemblyAI charges per audio hour with add-on pricing for intelligence features.

Prerequisites

• Access to AssemblyAI billing dashboard at https://www.assemblyai.com/app
• Understanding of current usage patterns

Actual Pricing (Pay-As-You-Go)

Speech-to-Text (Async)

Model	Price per Hour	Best For
Best (Universal-3)	$0.37/hr	Highest accuracy, production
Nano	$0.12/hr	High volume, cost-sensitive

Streaming Speech-to-Text

Model	Price per Hour
Universal Streaming	$0.47/hr

Audio Intelligence Add-Ons

Feature	Additional Cost per Hour
Speaker Diarization	$0.02/hr
Sentiment Analysis	$0.02/hr
Entity Detection	$0.08/hr
Auto Highlights	Included
Content Safety	$0.02/hr
IAB Categories	$0.02/hr
Summarization	Included (uses LeMUR)
PII Redaction	$0.02/hr
PII Audio Redaction	+processing time

LeMUR

Model	Price per Input Token	Price per Output Token
Default	~$0.003/1K tokens	~$0.015/1K tokens

Instructions

Step 1: Cost Estimation Calculator

interface CostEstimate {
  baseTranscriptionCost: number;
  featuresCost: number;
  totalCost: number;
  breakdown: Record<string, number>;
}

function estimateTranscriptionCost(
  audioHours: number,
  options: {
    model?: 'best' | 'nano';
    speakerLabels?: boolean;
    sentimentAnalysis?: boolean;
    entityDetection?: boolean;
    contentSafety?: boolean;
    iabCategories?: boolean;
    piiRedaction?: boolean;
  } = {}
): CostEstimate {
  const model = options.model ?? 'best';
  const baseRate = model === 'best' ? 0.37 : 0.12;
  const baseCost = audioHours * baseRate;

  const breakdown: Record<string, number> = {
    [`transcription (${model})`]: baseCost,
  };

  let featuresCost = 0;

  if (options.speakerLabels) {
    const cost = audioHours * 0.02;
    breakdown['speaker_labels'] = cost;
    featuresCost += cost;
  }
  if (options.sentimentAnalysis) {
    const cost = audioHours * 0.02;
    breakdown['sentiment_analysis'] = cost;
    featuresCost += cost;
  }
  if (options.entityDetection) {
    const cost = audioHours * 0.08;
    breakdown['entity_detection'] = cost;
    featuresCost += cost;
  }
  if (options.contentSafety) {
    const cost = audioHours * 0.02;
    breakdown['content_safety'] = cost;
    featuresCost += cost;
  }
  if (options.iabCategories) {
    const cost = audioHours * 0.02;
    breakdown['iab_categories'] = cost;
    featuresCost += cost;
  }
  if (options.piiRedaction) {
    const cost = audioHours * 0.02;
    breakdown['pii_redaction'] = cost;
    featuresCost += cost;
  }

  return {
    baseTranscriptionCost: baseCost,
    featuresCost,
    totalCost: baseCost + featuresCost,
    breakdown,
  };
}

// Example: 100 hours with Best model + diarization + sentiment
const estimate = estimateTranscriptionCost(100, {
  model: 'best',
  speakerLabels: true,
  sentimentAnalysis: true,
});
// Result: $37 (transcription) + $2 (speakers) + $2 (sentiment) = $41

Step 2: Model Selection Strategy

import { AssemblyAI } from 'assemblyai';

const client = new AssemblyAI({
  apiKey: process.env.ASSEMBLYAI_API_KEY!,
});

// Use Nano for high-volume, cost-sensitive workloads
// - 3x cheaper than Best ($0.12 vs $0.37)
// - Good enough for search indexing, keyword detection
const cheapTranscript = await client.transcripts.transcribe({
  audio: audioUrl,
  speech_model: 'nano',
});

// Use Best for critical, accuracy-sensitive workloads
// - Medical transcription, legal proceedings, compliance
// - Supports word_boost for domain terminology
const accurateTranscript = await client.transcripts.transcribe({
  audio: audioUrl,
  speech_model: 'best',
  word_boost: ['specialized', 'domain', 'terms'],
  boost_param: 'high',
});

Step 3: Feature Budget — Only Enable What You Need

// EXPENSIVE: All features enabled ($0.37 + $0.16 = $0.53/hr)
const expensive = await client.transcripts.transcribe({
  audio: audioUrl,
  speech_model: 'best',        // $0.37/hr
  speaker_labels: true,         // +$0.02/hr
  sentiment_analysis: true,     // +$0.02/hr
  entity_detection: true,       // +$0.08/hr
  content_safety: true,         // +$0.02/hr
  iab_categories: true,         // +$0.02/hr
});

// CHEAP: Only what's needed ($0.12 + $0.02 = $0.14/hr)
const cheap = await client.transcripts.transcribe({
  audio: audioUrl,
  speech_model: 'nano',         // $0.12/hr
  speaker_labels: true,         // +$0.02/hr
  // Skip features you don't use
});

Step 4: Usage Tracking

class AssemblyAIUsageTracker {
  private totalAudioHours = 0;
  private totalCost = 0;
  private transcriptionCount = 0;

  track(audioDurationSeconds: number, model: 'best' | 'nano', features: string[]) {
    const hours = audioDurationSeconds / 3600;
    this.totalAudioHours += hours;
    this.transcriptionCount++;

    const estimate = estimateTranscriptionCost(hours, {
      model,
      speakerLabels: features.includes('speaker_labels'),
      sentimentAnalysis: features.includes('sentiment_analysis'),
      entityDetection: features.includes('entity_detection'),
      contentSafety: features.includes('content_safety'),
      iabCategories: features.includes('iab_categories'),
      piiRedaction: features.includes('redact_pii'),
    });

    this.totalCost += estimate.totalCost;

    return estimate;
  }

  getSummary() {
    return {
      totalAudioHours: this.totalAudioHours.toFixed(2),
      totalCost: `$${this.totalCost.toFixed(2)}`,
      transcriptionCount: this.transcriptionCount,
      avgCostPerTranscription: `$${(this.totalCost / this.transcriptionCount).toFixed(4)}`,
    };
  }
}

Step 5: Cost Reduction Strategies

Strategy	Savings	Trade-off
Use Nano instead of Best	68% cheaper	Slightly lower accuracy
Disable unused features	Up to $0.16/hr	Missing insights
Cache transcript results	Eliminate re-fetch costs	Stale data risk
Use LeMUR instead of per-feature AI	Often cheaper for summaries	Different output format
Pre-filter audio (skip silence)	Proportional savings	Requires preprocessing
Batch with webhooks	No savings, but better throughput	More complex architecture

Step 6: Budget Alerts

const MONTHLY_BUDGET = 100; // $100
const tracker = new AssemblyAIUsageTracker();

// After each transcription
const estimate = tracker.track(transcript.audio_duration ?? 0, 'best', ['speaker_labels']);
const summary = tracker.getSummary();

if (parseFloat(summary.totalCost.replace('$', '')) > MONTHLY_BUDGET * 0.8) {
  console.warn(`Budget warning: ${summary.totalCost} of $${MONTHLY_BUDGET} used`);
  // Send alert to Slack, email, etc.
}

Output

• Accurate cost estimation with feature-level breakdown
• Model selection strategy (Best vs. Nano)
• Feature budgeting to eliminate unnecessary costs
• Usage tracking with budget alerts
• Cost reduction strategies ranked by impact

Error Handling

Issue	Cause	Solution
Unexpected high bill	Entity detection enabled everywhere	Audit features per endpoint
Nano accuracy too low	Wrong model for use case	Switch critical paths to Best
Budget exceeded	No monitoring	Implement usage tracker + alerts
Double billing	Re-transcribing same audio	Cache transcript IDs, check before submitting

Resources

• AssemblyAI Pricing
• AssemblyAI Billing Dashboard
• Speech Model Comparison

Next Steps

For architecture patterns, see assemblyai-reference-architecture.