Compare models

Put up to 4 models beside each other — token prices, context windows, capabilities and provider, from the same catalogue the model pages read.

Universal-3.5 ProAssemblyAI Remove
Aura-2Deepgram Remove
S2 ProFish Audio Remove
GPT-6 LunaOpenAI Remove

4 is the maximum. Remove one to add another.

universal-3-5-pro vs aura-2 vs s2-pro vs gpt-6-luna
Attribute	Universal-3.5 Prouniversal-3-5-pro	Aura-2aura-2	S2 Pros2-pro	GPT-6 Lunagpt-6-luna
Pricing
Input	$0 / 1M	$0 / 1M	$0 / 1M	$0.10 / 1M
Output	$0 / 1M	$0 / 1M	$0 / 1M	$0.50 / 1M
Cache Write (5m)	Not applicable	Not applicable	Not applicable	$0.10 / 1M
Cache Write (1h)	Not applicable	Not applicable	Not applicable	$0.10 / 1M
Cache Read	Not applicable	Not applicable	Not applicable	$0.10 / 1M
Web Search	$0 / 1M	$0 / 1M	$0 / 1M	$0 / 1M
Context
Max context	N/A	N/A	N/A	1.1M
Max output	N/A	N/A	N/A	N/A
Capabilities
Vision	No	No	No	Yes
Function Calling	No	No	No	Yes
JSON Mode	No	No	No	Yes
Streaming	No	No	No	Yes
Catalogue
Provider	AssemblyAI	Deepgram	Fish Audio	OpenAI
Category	voice	voice	voice	chat
Charge type	Pay As You Go	Pay As You Go	Pay As You Go	Pay As You Go
Released	2026-09-22	2026-07-16	2026-07-29	—
Description
Summary	AssemblyAI Universal-3.5 Pro speech-to-text. Billed per second of audio.	Deepgram Aura-2 text-to-speech for real-time voice applications. Billed per input character.	Fish Audio S2 Pro text-to-speech. Billed per UTF-8 byte of input text.	GPT-6 Luna is the fast, cost-efficient model in OpenAI's GPT-6 series, optimized for high-volume and latency-sensitive workloads such as chat, classification, and lightweight agentic tasks. It combines low-cost, responsive inference with the GPT-6 family’s improvements in factual reliability and clear, concise communication. At higher reasoning effort, GPT-6 Luna can also handle complex software engineering and computer-use workflows that previously required a Sol-tier model, making it a versatile choice for scalable production applications that need to balance speed, cost, and capability.