I haven't looked at any other details, but Googling Fastly says this: "Fastly, Inc. is an American cloud computing services provider. Fastly's edge cloud platform provides a content delivery network, Internet security services, load balancing, and video & streaming services" Just judging by that statement, I feel they're going to be eaten by AWS, GCP, and maybe Azure. However, it seems their focus may be on creating…
They are in the CDN/Edge space. Akamai and Cloudflare are more direct comparisons. AWS, GCP, and Azure have CDNs as well, but those are more typically used by existing customers to front things running there.
Fastly has deployments in 17 north american cities. AWS is in 5.
They're pretty different strategies. For every massive AWS datacenter on a continent, fastly has at least 3 tiny ones -- inevitably closer to your customers, meaning lower RTT.