Your public key is always clear text, or at a minimum your public key finger print (which can be used via a key-server to find your personal information and public key).
So GnuPG to a degree makes it difficult to hide metadata about yourself as many tools will send your public key + data to a key server as soon as they create your key-pair. This is so when people verify you, your easier to find.
This creates a chicken-in-the-box metadata problem where for people to very your public GnuPG public-key is really you that info has to be public, but for anonymity it can't be .
This is all true, but is a different question from deniability when sending messages, and leaking metadata when sending information, which is what tptacek claimed:
> ...in particular, it's difficult to send deniable messages with it.
It's easy (unless tptacek is mentioning an attack I am unaware of) to ensure deniability -- encrypt but don't sign.
Not sure what OP was getting at (maybe the difficulty of deniability using GPG/GPG-encrypted mail defaults), but you'd still be sending to a recipient's long-lived public key.
That's practically different than a system like OTR that has forward secrecy by default.
Since anyone in the world can encrypt to a PGP public key, deniability is trivial. It is true that some systems (like enigmail) also encrypt to your own public key when sending messages, but this is also easily deniable.
You usually want the recipient to be able to verify the sender, but not be able to prove it to a third party. Throwing away authentication entirely is a pretty baby-with-the-bathwater solution to deniability.
So GnuPG to a degree makes it difficult to hide metadata about yourself as many tools will send your public key + data to a key server as soon as they create your key-pair. This is so when people verify you, your easier to find.
This creates a chicken-in-the-box metadata problem where for people to very your public GnuPG public-key is really you that info has to be public, but for anonymity it can't be .