gpt-5.6 vs gpt-oss-120b

Capability for the money

gpt-5.6 is 25.0× dearer for 15.9 points on hard reasoning (GPQA Diamond) — worth it only if that is your bottleneck.

1. Following instructions

   extraction, classification, sticking to a format

   IFBench
   gpt-5.672.7%

   gpt-oss-120b69.0%

   gpt-5.6 +3.7

2. Tool use

   multi-step agent work against real tools

   τ²-bench
   gpt-5.685.1%

   gpt-oss-120b65.8%

   gpt-5.6 +19.3

3. Hard reasoning

   graduate-level science and multi-step analysis

   GPQA Diamond
   gpt-5.694.1%

   gpt-oss-120b78.2%

   gpt-5.6 +15.9

Averaged over the benchmarks both models sat, gpt-oss-120b returns 157.8 points of pass rate per dollar of blended price against 7.5 — the ratio that decides whether the dearer model earns its rate.

Each figure is a pass rate: the share of that test set the model answered correctly, measured by a third party rather than self-reported by the lab. Rows are different tests of different difficulty, so compare a model against the other model, not one row against the next. No published coding score for one of these models, so that lens is omitted. And a benchmark is not your workload — it narrows the shortlist, it does not pick for you.