Disclosure: I maintain Tura, where the full test record is published.
I ran 280+ Codex CLI sessions with GPT-5.6 Sol. In the current build, fewer commands per model turn can mean more turns and more cached-input cost.
Most benchmarks favor 5.6 Sol on cost per result: on DeepSWE, 5.5 High averaged USD 5.1 per task versus USD 3.5 for 5.6 Sol High. But in Codex CLI 0.144.1, my 5.6 Sol High runs were about 21% more expensive than 5.5 High.
The likely mechanism is orchestration: 5.5 explicitly uses multi_tool_use.parallel, while 5.6 mainly uses one top-level exec. I observed 0.97 versus 2.5 commands per model call, roughly 1.84× as many rounds, and 66.5% of 5.6 Sol High cost in cached input. Token-saving plugins did not materially lower that total; reducing unnecessary model rounds did.
Implementation reference: https://github.com/openai/codex/blob/rust-v0.144.1/codex-rs/core/src/tools/code_mode/execute_handler.rs#L20-L72
Full test record: https://turaai.net/docs#benchmark-current-test-set-record
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