Pricing: the 3x output delta is the deciding factor for most workloads
**GPT-5.5 lists at $5/1M input and $25/1M output. Claude Opus 4.7 lists at $15/1M input and $75/1M output.** Opus is 3x the input price and 3x the output price. That delta is not a small thing — for any workload that runs at scale, it's the dominant input to total cost of ownership, often more important than per-call quality differences.
**GPT-5.4** sits in between at $2.50/1M input and $15/1M output — half the GPT-5.5 price for ~95% of the quality on most tasks. Teams running production workloads where the marginal quality of 5.5 isn't worth 2x the cost typically default to 5.4. We see this split often: 5.5 for hard reasoning paths, 5.4 for the high-volume bread-and-butter calls.
**Caching changes the math materially.** Anthropic's 90% cache-read discount on Opus drops the effective input cost on cached prefixes from $15/1M to $1.50/1M — which makes Opus directly competitive with GPT-5.5 on workloads with long, repeated system prompts (RAG with stable instructions, agent harnesses with stable tool definitions). OpenAI's 50% prompt-cache hit discount on GPT-5.5 drops input to $2.50/1M on cache hits.
**Output is where Opus stays expensive.** No cache discount applies to output — and most agentic / coding workloads are output-heavy. A typical coding agent run that consumes 8K input and emits 4K output costs roughly $0.42 on GPT-5.5 vs $1.10 on Opus 4.7. At 10,000 runs/day, that's $4,200/day vs $11,000/day — a $2M/year delta.
**The right question is not 'which is cheaper'** — it's 'which closes the per-call quality gap enough to justify the output price difference at your actual call volume.' Use our Claude API cost calculator and OpenAI API cost calculator to plug your real input/output/cache-hit numbers in.