AI model comparison
Claude Sonnet 4.5 vs o3 Pro
Pricing, context window, benchmarks, and features compared side by side. Or skip the guesswork and send one prompt to both.
Anthropic
Claude Sonnet 4.5
Claude Sonnet 4.5 is Anthropic’s most advanced Sonnet model to date, optimized for real-world agents and coding workflows.
- Input / 1M
- $3
- Output / 1M
- $15
- Context
- 1M
OpenAI
o3 Pro
The o-series of models are trained with reinforcement learning to think before they answer and perform complex reasoning.
- Input / 1M
- $20
- Output / 1M
- $80
- Context
- 200K
At a glance
Quick verdict
How the two models stack up on the things people ask about most.
Lower price
Claude Sonnet 4.5
5.9x cheaper for a typical chat
Higher intelligence score
o3 Pro
21.9 vs 20.7 on Artificial Analysis
Larger context window
Claude Sonnet 4.5
1M vs 200K tokens
Newer release
Claude Sonnet 4.5
Released September 29, 2025
Benchmarks
Benchmark scores
Independent scores from Artificial Analysis. Higher is better.
Intelligence index
Claude Sonnet 4.520.7o3 Pro21.9Coding index
Claude Sonnet 4.552.1o3 ProNot availableAgentic index
Claude Sonnet 4.515.8o3 ProNot availablePricing
Claude Sonnet 4.5 vs o3 Pro API pricing
Per-token API rates. Cheaper option highlighted.
| Metric | Claude Sonnet 4.5 | o3 Pro |
|---|---|---|
| Input tokensPer 1M tokens | $3 | $20 |
| Output tokensPer 1M tokens | $15 | $80 |
| Cached input (read)Per 1M tokens | $0.30 | Not available |
| Cache writePer 1M tokens | $3.75 | Not available |
| Long-context pricingPer 1M tokens, for very long prompts | $6 in / $22.50 out above 200K | Same rate at any length |
| Web searchPer request | $0.01 | $0.01 |
What it costs in practice
Estimated cost per 1,000 requests at standard rates. Coding and long-document figures also show the cost when the input is already cached.
Chat message
2K in, 500 out
Claude Sonnet 4.5$13.50o3 Pro$80Coding task
30K in, 4K out
Claude Sonnet 4.5$150$69 cachedo3 Pro$920Long document summary
150K in, 2K out
Claude Sonnet 4.5$480$75 cachedo3 Pro$3160Specs
Context window and capabilities
How much each model can read, how much it can write, and what it accepts as input.
| Metric | Claude Sonnet 4.5 | o3 Pro |
|---|---|---|
| Context window | 1M tokens | 200K tokens |
| Max output | 64K tokens | 100K tokens |
| Input types | File, Image, Text | File, Image, Text |
| Output types | Text | Text |
| Reasoning effort levels | Not available | Not available |
| Default reasoning effort | Not available | Not available |
| Release date | September 29, 2025 | June 10, 2025 |
Features
Supported features
API features available for each model.
| Metric | Claude Sonnet 4.5 | o3 Pro |
|---|---|---|
| Tool calling | Supported | Supported |
| Structured outputs | Supported | Supported |
| JSON mode | Supported | Supported |
| Reasoning | Supported | Supported |
| Temperature | Supported | Not supported |
| Stop sequences | Supported | Not supported |
| Deterministic seed | Not supported | Supported |
| Verbosity control | Not supported | Not supported |
Keep exploring
More on these models
Other head-to-heads, the full model page, and the alternatives list for each model.
Claude Sonnet 4.5View full model details- Claude Sonnet 4.5 vs Claude Sonnet 4.6
- Claude Sonnet 4.5 vs Claude Haiku 4.5
- Claude Sonnet 4.5 vs Claude Opus 4.5
- Claude Sonnet 4.5 vs GPT-5.1
- Claude Sonnet 4.5 vs GPT-5.1-Codex
- Claude Sonnet 4.5 vs Gemini 2.5 Pro
- Claude Sonnet 4.5 vs GPT-5
- Claude Sonnet 4.5 vs Claude Opus 4.1
- Claude Sonnet 4.5 vs Qwen3.5 397B A17B
- Claude Sonnet 4.5 vs o3
- Claude Sonnet 4.5 vs Claude Sonnet 4
- Claude Sonnet 4.5 vs o1
Our take
Claude Sonnet 4.5 is 5.9x cheaper for a typical chat. o3 Pro scores higher on the Artificial Analysis Intelligence Index (21.9 vs 20.7). Claude Sonnet 4.5 has the larger context window (1M vs 200K tokens). The right pick depends on your workload, so the quickest way to settle it is to send the same prompt to both and compare.
FAQ
Frequently asked questions
Is Claude Sonnet 4.5 or o3 Pro cheaper?
Claude Sonnet 4.5 is cheaper for a typical chat (2K input tokens and 500 output tokens). Claude Sonnet 4.5 costs $3 per 1M input tokens and $15 per 1M output tokens, while o3 Pro costs $20 per 1M input tokens and $80 per 1M output tokens.
Which has a bigger context window, Claude Sonnet 4.5 or o3 Pro?
Claude Sonnet 4.5 supports up to 1M tokens of context, compared with 200K for o3 Pro.
Is Claude Sonnet 4.5 smarter than o3 Pro?
On the Artificial Analysis Intelligence Index, Claude Sonnet 4.5 scores 20.7 and o3 Pro scores 21.9, putting o3 Pro ahead. Benchmarks don't capture everything, so the best test is running your own prompts through both.
Can I use Claude Sonnet 4.5 and o3 Pro at the same time?
Yes. Shortcut Chat sends one prompt to multiple models at once, so you can see Claude Sonnet 4.5 and o3 Pro answer side by side and keep the better response.
Why choose? Ask both.
Send one prompt to Claude Sonnet 4.5 and o3 Pro at the same time. Compare the answers side by side and keep the best one.