Subsequently, he pursued graduate studies in mathematics at MIT, from 1972–73; he was tapped by Patrick Winston to become a permanent member of the AI Lab at MIT, but funding difficulties made it impossible to retain him. Gabriel tried to start up, with Dave Waltz, an AI Lab at the University of Illinois, but after two years the lab fell through due to general apathy. Gabriel did in this time period manage to earn an MS in Mathematics however (1973–1975).
On the strength of some of his mathematical work, Gabriel was then admitted to Stanford University; during that period (1975–1981), he served as a Teacher’s Assistant to John McCarthy, the founder of Lisp; he ported Maclisp from its native ITS to WAITS; he earned a PhD. in Computer Science (on the topic of natural language generation); and he and his wife Kathy had a son. Around this time period, he became a spokesperson for the League for Programming Freedom.
After he earned the PhD, he continued to work on AI projects for McCarthy, although his thesis advisor was Terry Winograd. He eventually began working for Lawrence Livermore National Labs, where he recruited a number of the brightest researchers and programmers for a company he founded in 1984 (and would leave in 1992), and would survive until 1994, Lucid, Incorporated.
Gabriel was at various times the President and Chairman of Lucid Inc. The product the company shipped was an integrated Lisp IDE for Sun Microsystems’ RISC hardware architecture. This sidestepped the principal failure of Lisp machines by, in essence, rewriting the Lisp machine IDE for use on a more cost-effective and less moribund architecture. During this time period, Gabriel married his second wife, and had a daughter; the two divorced in 1993.
Eventually Lucid’s focus shifted (during the AI Winter) to an IDE for C++. A core component of the IDE was Richard Stallman’s version of Emacs, GNU Emacs. GNU Emacs was not up to Lucid’s needs, however, and several Lucid programmers were assigned to help develop GNU Emacs. Friction arose between the programmers and Stallman over how to handle GUI issues, and Lucid forked; thus they were primarily responsible for the birth of what would come to be called XEmacs. One of his hires was another notable programmer Jamie W. Zawinski.
After Gabriel left Lucid, Inc. for good, he became a Vice President of Development for Parc Place Systems, Inc. (1994–1995), and then a consultant, for, among others, Sun Microsystems and Aspen Smallworks. In 2007, he joined IBM Research as a Distinguished Engineer.
In 1998 he received his MFA in Poetry from Warren Wilson College. He has published poems in a number of literary journals. His chapbook, Drive On, was published by Hollyridge Press in 2005.
Gabriel is the recipient of ACM's 1998 Fellows Award and the 2004 Allen Newell Award. The citation reads: “For innovations not only on fundamental issues in programming languages and software design but also on the interaction between computer science and other disciplines, notably architecture and poetry.”
He is the conference chair of the 2007 OOPSLA.