According to those graphs, Grok 4.5 appears to be the most cost-effective model.
$0.05 per task, Intelligence Index score 52 -> GPT 5.6 Luna max
$0.36 per task, Intelligence Index score 56 -> Grok 4.5 high
$1.13 per task, Intelligence Index score 58 -> Qwen 3.8 Max
$0.81 per task, Intelligence Index score 59 -> GPT 5.6 Sol xhigh
$1.80 per task, Intelligence Index score 63 -> Opus 5 xhigh
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$0.05 per task, Intelligence Index score 52 -> GPT 5.6 Luna max
$0.36 per task, Intelligence Index score 56 -> Grok 4.5 high
$1.13 per task, Intelligence Index score 58 -> Qwen 3.8 Max
$0.81 per task, Intelligence Index score 59 -> GPT 5.6 Sol xhigh
$1.80 per task, Intelligence Index score 63 -> Opus 5 xhigh