Is AION 2 free to play?

Yes. From 5 October anyone can download AION 2 on Steam or PURPLE and play it without paying. Money buys an earlier start, a membership that opens up buying from other players, and a shop of cosmetics, consumables and pass upgrades.

“AION 2 is free to play and is accessible to every player with no purchase required. How you invest is entirely up to you.”

(From NC notice: Team Update (the business model))

What costs money

WhatPriceWhat it gets you
Founder's Pack$24.99 / $49.99 / $99.99Five days of Early Access from 30 September, 30 days of membership, starter consumables and cosmetics. Sold until Early Access ends.
Special Quai Membership$15 for 30 daysBuying on the Market, the World Market, the Kina and Quna exchange, remote storage and more, on one server.
QunaNot published yetThe premium currency. Buys shop items and the paid pass track, and buys Kina from other players on the exchange.
Shop cosmeticsNot published yetOutfits, wings, pets, weapon skins and accessories. NC says they give no gameplay or combat advantage.
Shop consumablesNot published yetPotions, resurrection stones and similar. NC says the same items can be earned by playing.
Daeva Pass, premium trackBought with QunaExtra rewards on top of the free track, sold per character.

NC has not published Quna prices or shop prices in its English notices. The packs and what binds to one character are compared on Founder’s Packs compared; the membership has its own page at membership cost.

Two panels from NC's notice under the heading In-Game Shop: Cosmetics, listing outfits, wings, pets, weapon skins and accessories, and Consumables
The In-Game Shop section of NC's business model notice: cosmetics on the left, consumables on the right. Image: NC, from the Team Update notice on the official AION 2 site.

What a free account cannot do

The real line between free and paying is the membership, not the shop. NC’s membership notice lists what changes when it is active; the left column is what you get without it:

FeatureWithout membershipWith membership
MarketItems can be listed for sale; buying is unavailableListing and buying
World MarketItems cannot be listed or purchasedItems can be listed and purchased
ExchangeUnavailableKina and Quna can be exchanged
StorageOnly through Storage NPCsRemote Storage, always available from your Cube
Wind Breeze MerchantsOnly through Merchant NPCsOpen from the shop menu
Odyle Energy on reward CubesInjected once (Expedition and Transcendence)Injected twice (Expedition, Transcendence and Sanctuary)
Odyle Energy capacityBase capacityIncreased; NC has not said by how much

Two NC texts disagree slightly here. The business model notice says an active membership is required to trade on the Market at all, while the later membership notice says a free account can still list items for sale and only buying is locked. The membership table is the more detailed of the two, which is why it is used above.

How far free goes

Kina, the currency the Market runs on, is earned by playing, and the Daeva Pass has a free standard track for every character. NC’s business model notice names no other paid gate on levelling, classes or dungeons. NC describes no way to earn Quna by playing: the only route it mentions from Kina to Quna is the exchange, and that needs a membership, whichever side of the trade you are on. How much that Kina-for-money route matters for power is weighed on is AION 2 pay to win, and how the two currencies work day to day is on Kina and Quna.

If you only want to try it, wait for 5 October and install it free; download and install covers both launchers.