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AssemblyAI vs OpenAI API: pricing, quotas & features (2025)

Best-in-class speech-to-text API — Universal models, 99 languages, low-latency streaming
vs. Frontier models: GPT-5, o-series reasoning, image, audio, embeddings

Data sourced from vendor documentation · Last updated May 2026

AssemblyAI website ↗OpenAI Platform ↗

Summary

AssemblyAI and OpenAI API are both ai-api platforms, addressing the same core use case with different implementation philosophies and trade-offs. Both offer a free tier, making it easy to prototype without a credit card. OpenAI API has a broader documented feature set (12 vs 11 features). The right choice depends on your existing stack, team experience, and feature requirements. All pricing and quota data below is sourced from AssemblyAI and OpenAI API's official documentation — not generated by AI or estimated.

AssemblyAI vs OpenAI API: Comparativa de precios, cuotas y características (2025)

En esta comparativa analizamos AssemblyAI y OpenAI API lado a lado — incluyendo precios mensuales, límites del tier gratuito, características técnicas, cuotas de uso (almacenamiento, transferencia, usuarios activos mensuales) y los interfaces de desarrollo disponibles. Todos los datos proceden de la documentación oficial de cada proveedor, no de respuestas generadas por IA.

AssemblyAI es una plataforma de la categoría ai-api — Best-in-class speech-to-text API — Universal models, 99 languages, low-latency streaming. Ofrece 3 tiers de precio: Free Credits gratuito, Pay-as-you-go gratuito, Enterprise (personalizado). Su catálogo en Staxly documenta 11 características y 7 interfazes para desarrolladores.

OpenAI API pertenece a la categoría ai-api — Frontier models: GPT-5, o-series reasoning, image, audio, embeddings. Ofrece 4 tiers de precio: Free Tier (Trial) gratuito, Pay-as-you-go gratuito, Usage Tiers (1-5) gratuito, Enterprise (personalizado). Su catálogo documenta 12 características y 7 interfazes para desarrolladores.

A continuación encontrarás los tiers de precio completos de ambas plataformas, una matriz de cuotas del tier gratuito (transferencia, almacenamiento, MAU, llamadas a la API y otros límites), el listado completo de características y los interfaces (CLI, SDKs, REST, GraphQL, MCP) disponibles para integrar cada servicio.

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Pricing tiers

AssemblyAI

Free Credits
$50 in free credits on signup. Full API access.
Free
Pay-as-you-go
Per-hour billing by model. No minimum.
$0 base (usage-based)
Enterprise
Custom contracts. SLA, private deployments, BAA.
Custom
AssemblyAI website ↗

OpenAI API

Free Tier (Trial)
$5 free credit for new accounts. Rate-limited.
Free
Pay-as-you-go
No monthly min. Per-token pricing by model.
$0 base (usage-based)
Usage Tiers (1-5)
Automatic tier promotion based on cumulative spend. Higher tiers = higher rate limits + new model access.
$0 base (usage-based)
Enterprise
Custom. Priority access, SLA, dedicated capacity.
Custom
OpenAI Platform ↗

Free-tier quotas head-to-head

Comparing free-trial on AssemblyAI vs free-tier on OpenAI API.

MetricAssemblyAIOpenAI API
No overlapping quota metrics for these tiers.

Features

AssemblyAI · 11 features

  • Advanced Prompting — Streaming with disfluency + code-switching + realtime diarization.
  • Audio Intelligence — Sentiment, topic detection, summarization, entity detection, content safety, IAB…
  • Auto Punctuation — Smart capitalization + punctuation.
  • Keyterm Prompting — Boost accuracy for domain vocabulary.
  • LeMUR (LLM framework) — Run LLMs over transcripts: Q&A, summary, action items.
  • Medical Mode — Specialized for clinical + medical vocabulary.
  • PII Redaction — Auto-redact credit cards, SSNs, addresses, emails.
  • Pre-recorded Transcription — Upload audio/video URL or file → transcript.
  • Realtime Streaming — WebSocket-based low-latency STT.
  • Speaker Diarization — Identify who spoke when.
  • Webhooks — Auto-notify when transcription finishes.

OpenAI API · 12 features

  • Assistants API — Stateful assistants with tools, threads, file search.
  • Batch API — 50% discount for async processing within 24h.
  • Chat Completions API — Classic /v1/chat/completions endpoint.
  • Files API — Upload docs for retrieval, fine-tuning, batch.
  • Fine-Tuning — Supervised + DPO fine-tuning for GPT-4o, GPT-4.1, GPT-4o-mini.
  • Function Calling — JSON-schema tool calling; parallel calls supported.
  • Moderation — Safety classifier API (free).
  • Prompt Caching — Auto-cache repeated prefixes; 50% cheaper cached hits.
  • Realtime API — WebSocket streaming voice + text with low latency.
  • Responses API — Stateful conversational API.
  • Structured Outputs — Enforced JSON schema compliance.
  • Vision — Image input for GPT models.

Developer interfaces

KindAssemblyAIOpenAI API
SDKassemblyai (Node), assemblyai (Python), assemblyai (Ruby), assemblyai-goopenai-dotnet, openai-go, openai-node, openai-python
RESTAssemblyAI REST APIOpenAI REST API
MCP—OpenAI MCP
OTHERStreaming WebSocket, WebhooksRealtime API (WebSocket)

Key takeaways

  • Both AssemblyAI and OpenAI API offer a free tier — AssemblyAI ("Free Credits") and OpenAI API ("Free Tier (Trial)") — with no credit card required to start.
  • OpenAI API has a broader documented feature set (12 features) vs. AssemblyAI (11 features) in Staxly's catalog.
  • Developer integrations differ: only OpenAI API offers MCP.
Staxly is an independent catalog of developer platforms. Some links to AssemblyAI and OpenAI API may be affiliate links — Staxly may earn a commission if you sign up through them, at no extra cost to you. Pricing is verified against vendor pages at publication time — reconfirm before buying.

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