Names that sound like poetry
Haiku, Sonnet, Opus, Fable. Luna, Sol, Astra. One company, a whole lineup of models. Which one should you pick?
Like a scooter, a car and a truck
Think of it like choosing a vehicle. The same company makes scooters, cars and trucks. No vehicle is "the best", only the right one for the job.
SMALL TIER
Fast and cheap
Small models like Anthropic's Haiku or OpenAI's Luna answer fast and cost very little. They suit simple tasks done in large amounts.
MIDDLE TIER
Balanced
Middle models like Sonnet or Sol balance quality, speed and price. They're the default choice for most everyday work.
LARGE TIER
Very powerful
Large models like Opus or Astra reason deeply and handle hard tasks, but they're slower and much more expensive.
TOP TIER
Anthropic's Fable
Fable is the top tier Anthropic added in mid-2026, above even Opus. It's made for very long, very hard work, like letting an AI agent run a whole project for hours. It's also the most expensive tier.
The real price gap
The gap is big. With OpenAI, the largest tier costs about a hundred times more than the smallest for the same amount of text.
This article is based on the video Haiku, Sonnet, Opus, Fable; Luna, Sol, Astra: what's the difference? Which model for which job from the Mark học AI channel. Watch the video (in Vietnamese) to see the animations.