Opposing Force received a very favorable reception from critics, holding a score of 85.45% on the review aggregator site GameRankings. The deal was signed, and the production of the Opposing Force expansion pack went forward. Newell, inspired by The Alexandria Quartet series of novels, also wanted to have a Rashomon-esque structure and allow the players to experience the same events from a different point of view. He likened the concept to the play Rosencrantz and Guildenstern Are Dead. Randy Pitchford pitched the idea of player returning to Black Mesa as one of the soldiers invading the facility occurring during the same time as the events of Half-Life, retelling the story from another character's perspective. Both companies got together to discuss and explore the possibilities.

Through their connections, Gabe was told what Gearbox was doing, and he believed they'd be a good fit. However, Gabe Newell ended up calling them first as he a similar idea for a project. Gearbox had connections at Valve and were interested in meeting them to see what they could put together. They were looking for someone to take over their role and expand the Half-Life universe so they could focus on their future titles. Meanwhile, Valve was busy with developing Half-Life 2 and its supporting engine technology.

The team wanted to work on small scale titles based on an existing technology rather than creating a completely new game.

At the time, Gearbox was a new company formed by the core members of the defunct Rebel Boat Rocker which had been shut down after a struggle with their publisher on their first video game project. Half-Life: Opposing Force was announced on Apto be developed by Gearbox Software.

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