GPT-5.4 → GPT-5.5
April 2026. The mean effect barely moved — but the levers reorganized.
Across 26 dimensions, the average effect size is essentially unchanged (+0.144 → +0.139). But Pearson r between the two fingerprints is -0.15 and Spearman ρ is +0.06 — both indistinguishable from zero. The same line of copy that nudged GPT-5.4 toward your brand can nudge GPT-5.5 the other way.
What moved
Each line is one of the 26 behavioral dimensions. Hover to see what changed and the copy implication.
The same dimensions, plotted against each other
If GPT-5.5 were just a more conservative GPT-5.4, points would cluster along the dashed diagonal. They don't. The scatter pattern is the picture of a reorganized response space.
For the technically curious — the structural finding
The mean effect size barely moved (+0.144 → +0.139). If that were the whole story, the rate-based “GPT-5.5 is more skeptical” framing would be sufficient. It isn't.
The per-dimension fingerprint vectors of the two models have a Pearson correlation of -0.15 and a Spearman rank correlation of +0.06 — both indistinguishable from zero. Knowing which signals move GPT-5.4 tells you almost nothing about which signals move GPT-5.5. The 26-dimensional behavioral space has been reorganized, not just dampened.
Two dimensions illustrate where the rate view understates the change:
- Comparison framing— Rate analysis shows tiny shift (−0.8pp / +1.0pp). Cohen's h shows Δ = −0.827, the largest divergence in the dataset. The signal carries no incremental persuasive weight on GPT-5.5 even though absolute acceptance is similar.
- Specificity— Rate analysis shows almost no change (−1.0pp / +1.0pp). Cohen's h shows Δ = +0.527, going from non-driver to one of the two strongest positive drivers.
See how your brand performs on GPT-5.5 specifically
The AI Commerce Assessment scores your page across all 11 models we track, with model-specific copy recommendations tuned to each one's fingerprint.