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.

S2 ProFish Audio Remove
S2.1 ProFish Audio Remove
GPT-6 LunaOpenAI Remove
Universal-3.5 ProAssemblyAI Remove

4 is the maximum. Remove one to add another.

s2-pro vs s2.1-pro vs gpt-6-luna vs universal-3-5-pro
Attribute	S2 Pros2-pro	S2.1 Pros2.1-pro	GPT-6 Lunagpt-6-luna	Universal-3.5 Prouniversal-3-5-pro
Pricing
Input	$0 / 1M	$0 / 1M	$0.10 / 1M	$0 / 1M
Output	$0 / 1M	$0 / 1M	$0.50 / 1M	$0 / 1M
Cache Write (5m)	Not applicable	Not applicable	$0.10 / 1M	Not applicable
Cache Write (1h)	Not applicable	Not applicable	$0.10 / 1M	Not applicable
Cache Read	Not applicable	Not applicable	$0.10 / 1M	Not applicable
Web Search	$0 / 1M	$0 / 1M	$0 / 1M	$0 / 1M
Context
Max context	N/A	N/A	1.1M	N/A
Max output	N/A	N/A	N/A	N/A
Capabilities
Vision	No	No	Yes	No
Function Calling	No	No	Yes	No
JSON Mode	No	No	Yes	No
Streaming	No	No	Yes	No
Catalogue
Provider	Fish Audio	Fish Audio	OpenAI	AssemblyAI
Category	voice	voice	chat	voice
Charge type	Pay As You Go	Pay As You Go	Pay As You Go	Pay As You Go
Released	2026-07-29	2026-07-29	—	2026-09-22
Description
Summary	Fish Audio S2 Pro text-to-speech. Billed per UTF-8 byte of input text.	Fish Audio S2.1 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.	AssemblyAI Universal-3.5 Pro speech-to-text. Billed per second of audio.