GPT-5.5 Pro vs o3 Pro: reasoning-tier API pricing compared
o3 Pro is significantly cheaper on both inputs and outputs, representing a much more economical high-end reasoning option.
Pro-tier specialized reasoning comparison.
For complex planning and specialized deep thinking, Pro-tier reasoning models are unparalleled. Let's look at the pricing for GPT-5.5 Pro and o3 Pro.
By TechCompare · Updated
Cost Comparison
Based on 100,000 input tokens (50% cached), 5,000 output tokens, and 100 requests.Prices are fetched live from OpenRouter and may include temporary promotional discounts not accounted for in our article and comparison figures.
Side-by-side specs
| Spec | GPT-5.5 Pro | o3 Pro |
|---|---|---|
| Input Cost (per M) | $30.00 | $20.00 (better on this spec) |
| Output Cost (per M) | $180.00 | $80.00 (better on this spec) |
| Cached Input (per M) | $30.00 | $20.00 (better on this spec) |
| Batch Discount | 50% | 50% |
How they differ
GPT-5.5 Pro costs $30.00 per million input tokens and $180.00 per million output tokens, without caching discounts. o3 Pro is priced at $20.00 per million input tokens and $80.00 per million output tokens, also without caching discounts.
Verdict
On the base rows o3 Pro runs $20.00/M input against $30.00/M and $80.00/M output against $180.00/M, which is 1.5x cheaper on input and 2.25x cheaper on output. Neither model offers a cache discount, so cached input mirrors the base gap, and the 50% batch mode preserves the same ratio. At 100 calls per day for 30 days, assuming 100K input and 25K billed output tokens per call without batch discounts, o3 Pro saves $10,500 per month ($12 versus $15.50 per call). The choice between them is about reasoning ergonomics and OpenAI-tool integration, not the price line.
Which should you pick?
Choose GPT-5.5 Pro
OpenAI-integrated advanced software tasks and custom planning layers.
Choose o3 Pro
High-end reasoning, complex math proofs, and cost-effective deep thinking pipelines.