Short answer
For a new production API integration, neither is a straightforward default today. OpenAI’s API documentation marks GPT-4.5 Preview as shut down. It marks o3 deprecated and names GPT-5 as its successor. So GPT-4.5 is not an available API choice according to its model page; o3’s deprecation makes it a risky starting point for a new system. Check your API account’s model access and the model’s shutdown information before routing production traffic. (developers.openai.com)
If you’re comparing their original design, GPT-4.5 emphasized broad knowledge and natural, creative conversation; o3 was positioned for difficult, multi-step reasoning across text, code, and images. That is a difference in intended strengths—not proof that either one performs better on your application. The sources captured here do not provide a controlled, direct GPT-4.5-versus-o3 evaluation. (openai.com)
GPT-4.5 vs o3 at a glance
| Decision point | GPT-4.5 Preview | o3 |
|---|---|---|
| API lifecycle | OpenAI’s API model page says Shut down. | OpenAI’s model page marks it Deprecated and says it is succeeded by GPT-5. That does not, by itself, confirm whether your organization can still call it or give a shutdown date. |
| Original positioning | A research preview focused on scaling pre-training, with an emphasis on broad knowledge, recognizing patterns, natural conversation, and creative insight. | A reasoning model for multi-step problems involving text, code, and images; OpenAI describes strengths in math, science, coding, and visual reasoning. |
| Documented context and output limits | The model page is for a shut-down preview, not a currently usable API option. Its page lists historical specifications; don’t use them to plan a new integration. | The model page lists a 200,000-token context window and up to 100,000 output tokens. Confirm account-level availability and lifecycle before relying on these specifications. |
| Current listed API price | No current purchase price: the model is marked shut down. Its historical listed rates were $75 per million input tokens, $37.50 per million cached input tokens, and $150 per million output tokens. | The model page lists $2 per million input tokens, $0.50 per million cached input tokens, and $8 per million output tokens. Because o3 is deprecated, confirm availability and shutdown information in your API account before treating these as usable rates. |
| Practical choice | Don’t select it for a new API build based on historical descriptions or prices. | Consider only if it remains available to your organization and your workload benefits enough from its reasoning capabilities to justify adopting a deprecated model. |
The lifecycle labels and o3 specifications and rates above come from OpenAI’s model pages. The GPT-4.5 price is included as historical context only, not as a current quote. (developers.openai.com)
Which model was better for which tasks?
GPT-4.5 was positioned for fluent, creative, knowledge-rich interaction. At launch, OpenAI described it as a research preview built around scaling pre-training and post-training, with potential strengths in natural conversation, understanding user intent, writing, and creative insight. These are product-positioning claims, not a head-to-head result against o3. (openai.com)
o3 was positioned for harder, multi-step reasoning. OpenAI describes o3 as a model for problems involving analysis across text, code, and images, and highlights math, science, coding, visual reasoning, technical writing, and instruction following. That description can help you identify what to test, but it does not promise a particular result on your own workload. (developers.openai.com)
Don’t substitute o3-mini benchmark results for o3 results. A March 2025 Helicone article reports GPT-4.5 comparisons against o3-mini, including different leaders on two coding benchmarks; those figures are not evidence of how full o3 compares with GPT-4.5.
API status: verify before building
OpenAI’s current API model page labels GPT-4.5 Preview as shut down. OpenAI’s API announcement had said the preview would be turned off on July 14, 2025. GPT-4.5’s former preview identifier and historical code examples should not be treated as working API instructions. (developers.openai.com)
OpenAI’s o3 page labels o3 deprecated and says it has been succeeded by GPT-5. The page still displays model details and prices, but a listing is not a guarantee that the model is available to your organization or suitable for a new production dependency. OpenAI recommends checking a model’s shutdown_date through the List models or Retrieve a model API endpoints; check your account’s access as well. (developers.openai.com)
That distinction matters: deprecated does not necessarily mean already shut down, while a published price does not mean the model is currently available to every API customer. Before deploying or migrating, verify the model ID, access, and shutdown date for the organization that will make the requests. (developers.openai.com)
Historical API cost comparison—and a worked estimate
GPT-4.5’s API page lists historical rates of $75 per million input tokens, $37.50 per million cached input tokens, and $150 per million output tokens. The o3 page lists $2 per million input tokens, $0.50 per million cached input tokens, and $8 per million output tokens. Those figures make o3’s listed rates much lower, but they do not make this a current purchasing comparison: GPT-4.5 is shut down, and o3 is deprecated. (developers.openai.com)
Illustrative o3 calculation: suppose one request uses 100,000 input tokens and 10,000 output tokens, all billed at the listed standard rates. Input would cost 100,000 ÷ 1,000,000 × $2 = $0.20; output would cost 10,000 ÷ 1,000,000 × $8 = $0.08; total: $0.28. This is a hypothetical token-cost calculation, not a measured workload or a current availability guarantee. Cached input, actual token use, and any applicable processing or tool charges can change a real bill. (developers.openai.com)
How to make the production decision
- Check lifecycle and access first. Confirm the exact model ID, account access, and any announced shutdown date. If GPT-4.5 is shut down for your intended API use, it is not a viable production choice. If o3 is deprecated, weigh the migration risk before adopting it for a new system. (
developers.openai.com) - Define the workload. Write down representative tasks, the quality bar, latency target, input/output token mix, and whether image inputs or multi-step reasoning are essential. No workload was specified here, so a stronger task-specific winner cannot be justified.
- Evaluate a supported candidate on representative requests. Compare answer quality, formatting, tool behavior where relevant, latency, errors, and cost. OpenAI’s migration guidance likewise recommends establishing a baseline on representative requests and comparing quality, latency, and cost before moving production traffic. (
help.openai.com) - Choose a currently supported model, not just the historical winner. OpenAI’s current model-selection page recommends its newer GPT-6 models for different needs, including complex reasoning and coding, balancing intelligence and cost, or cost-sensitive high-volume workloads. Consider a supported successor rather than building around a shut-down or deprecated option. (
developers.openai.com)
Bottom line: GPT-4.5 vs o3 is useful as a comparison of two different model approaches, but not as a clean production purchase choice in November 2026. GPT-4.5’s API model page says it is shut down; o3’s page says it is deprecated. For a new deployment, verify access and lifecycle, then evaluate a currently supported model against your actual workload.
Sources
GPT-4.5 Preview Model | OpenAI API
Introducing GPT-4.1 in the API | OpenAI