Mario, the creator of Pi terminal agent, has this great blog post[0]. He talks about how TerminalBench's highest scores comes from using the Terminus 2 harness which uses tmux under the hood.

When I was reading the Opus 4.6 launch post, they mentioned the same thing and their TerminalBench score was based on using Terminus 2 and not CC.

0. https://mariozechner.at/posts/2025-11-30-pi-coding-agent/