Upon visiting either the JSON or YAML folders of twilio-oai/spec, you'll notice a long list of files instead of a single specification. This is because Twilio's API spans multiple subdomains, such as api.twilio.com, accounts.twilio.com, flex-api.twilio.com, and many others.
Each file corresponds to one of these subdomains, which can be determined by looking at the servers property of any of the described endpoint paths in a given file.
For example, in twilio_acounts_v1.json, you'll find the following top-level property:
_10 "servers": [_10 {_10 "url": "https://accounts.twilio.com"_10 }_10 ],
This indicates that the file corresponds to the accounts.twilio.com subdomain. This same process can be applied to all spec files.