Apologies if this has been covered before; I'm not sure how to search on this subject. An agent just requested my full manuscript. Naturally, I have queried other agents, and not heard back from them yet. Is it permissible to inform these other agents about the request for the MS, or should I wait until I get an offer of representation before I notify them?
You wait for an offer. A full request is nothing. Don't get me wrong, it's a big, positive step, but you've still got a ways to go. Out of hundreds of full requests, the agency might pick three to represent. There really isn't much to "pit" at the agency stage. There's no money involved until a deal is reached with a publisher, then it becomes a different ballgame. But should you be lucky enough to have multiple offers of representation, I guess you would weigh which agent you think can get you better placement or a better deal. I mean Stephen King's agent is probably better than the agent equivalent of Joe Schmoe. Good luck!
And to be honest even when (if) you get an offer there’s no need to tell the other agents you’ve queried unless they come to you you’re not going to have agents competing to represent you unless you are Steven king or James Patterson and the like
Check the submission guidelines for the other agents you've queried. I know a few that ask you keep them updated with other full requests or offers of representation.
I've heard that *IF* you get an offer of representation it's OK to send a message to any agents with outstanding queries with a subject line of 'Offer Received' and I'm not sure how the rest of the subject line or email should read (maybe the same as the original email you sent?), but it's just a courtesy in case they want to move it up in their queue or take another look at it, not an attempt to play them off each other. But this is purely anecdotal and I wouldn't do it if the agent guidelines say not to do it. reddit r/pubtips may have more info.