I doubt the free model is sustainable long term. I think an ads-based #crypto-economic model could be a viable option for #Nostr #relays. The protocol could issue a crypto to #relay owners when ads are seen. Advertisers would need to burn the crypto to run ads.

> Why would I create a free relay on #nostr? What are the incentives to do it?

If you mean free as in a public, open, and free to use relay, there is no other incentive than to "support the case" and to help nostr grow. I've hosted a free relay since April 2022 and haven't earned a dime on it (costs about $50 a month as it is scaled up to host a lot of users). I do however continue to offer the relay service for free in the hopes that it helps bootstrap newcomers migrating from their favorite censored platform. Most people today aren't accustomed to pay for the social media service they use and often forget that running such services actually has real monetary costs. Therefore, it might be easier to onboard them to free relays first and then they can play around with paid relay services afterwards.

> Will free relays survive on Nostr

Yes. You could easily host a free relay in which only a certain set of npubs can write to, such as your friends/family, your local community, your online community, etc.

Offering a free and public relay, in which any npub can read and write to, requires you to scale up your hardware resources as the daily active users increases. That means that it might become economically inviable for one person to offer the service for free if the userbase grows big enough. When a relay becomes that big, it might make sense to partner up with some company to get them to pay the server costs and to give some kind of service in return such as an advertisement. If not, you have to either loose money for the cause or make the users pay so that you at least go even.

All in all, it depends on how many users you want to offer your relay service to. Some free relays will survive just fine, some will not.