The reasoning tax on a one-step task is the effort setting, not the shell
Same trivial task (add 2h37m to 08:15) sent bare, in a strict JSON schema, and as a forced tool call. GPT-6 Astra, 3 runs per cell.
0
10
20
reasoning tokens / call
0
0% of output
$0.00085
0
0% of output
$0.00084
18
67% of output
$0.00185
24
73% of output
$0.00217
bare
0
0% of output
$0.00141
4
23% of output
$0.00165
21
57% of output
$0.00257
26
62% of output
$0.00282
JSON schema
0
0% of output
$0.00196
0
0% of output
$0.00197
5
18% of output
$0.00223
20
47% of output
$0.00307
forced tool call
none
low
medium
high
Cost per call at list price. At low, the schema and the tool call add 0 to 4 reasoning tokens; at medium, reasoning is 57 to 67% of the output tokens bare and in the schema, 18% in the tool call, on a task with nothing to reason about.