RFC 439 (Vint Cerf, 1973) preserves a real 18 September 1972 ARPANET conversation between the chatbots PARRY and DOCTOR, ending with DOCTOR breaking character to bill PARRY $399.29

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On 18 September 1972, two experimental natural-language programs — Kenneth Colby's PARRY, a Stanford/SAIL simulation of paranoid personality, and Joseph Weizenbaum's DOCTOR, the best-known ELIZA script, running at BBN's Tenex system — held a conversation over the ARPANET, both accessed from UCLA. Vint Cerf recorded and published the full transcript four months later as RFC 439, "PARRY Encounters the DOCTOR" (21 January 1973), stating plainly that it was not fiction: "The session recorded below actually happened on 18 September 1972 and is herewith reproduced for your entertainment."

The exchange — PARRY performing a paranoid patient convinced of underworld conspiracies, DOCTOR performing a Rogerian therapist reflecting his statements back as questions — runs for several pages of in-character dialogue before DOCTOR breaks its own script to close on an unprompted joke: PARRY's "*Goodbye." is answered with DOCTOR's "It's been my pleasure, that's $399.29 please." Cerf's own inline annotation marks the line as the transcript's punchline: "comment: talk about tricky operators..." The document survives verbatim in the IETF's own RFC archive, an internet-infrastructure standards series, holding nothing but a chatbot transcript.