High-volume, cost-sensitive work
Choose o3
o3 costs 13% less on a typical mix of three input tokens for every output token ($3.50 against $4.00 per million tokens).
Claude Sonnet 5.5 vs o3: price, context and capabilities
Choose Claude Sonnet 5.5 for reused prompts and documents (RAG, agents), very long inputs, reasoning over long documents, the latest release and the most recent knowledge. Choose o3 for high-volume, cost-sensitive work and writing and code generation.
In short
- o3 is 13% cheaper than Claude Sonnet 5.5 at the headline price ($3.50 / 1M tokens vs $4.00 / 1M tokens).
- Claude Sonnet 5.5 reads more per request: 1M tokens against 200k.
- Claude Sonnet 5.5 is the newer model (September 2026, against Apr 16, 2025).
Which should you choose?
Each answer below comes straight from the published prices, specifications and independent benchmark results.
Writing and code generation
Choose o3
o3 charges $8.00 per million output tokens, against $10.00 for Claude Sonnet 5.5. Output dominates the bill when answers are long.
Reused prompts and documents (RAG, agents)
Choose Claude Sonnet 5.5
Claude Sonnet 5.5 charges $0.10 per million cached input tokens, against $0.50 for o3.
Very long inputs
Choose Claude Sonnet 5.5
Claude Sonnet 5.5 reads up to 1M tokens per request, against 200k for o3.
Reasoning over long documents
Choose Claude Sonnet 5.5
Claude Sonnet 5.5 scores 82.7% on Long-context reasoning (AA-LCR), against 74.7% for o3.
Latest release
Choose Claude Sonnet 5.5
Claude Sonnet 5.5 is the newer release (September 2026, against Apr 16, 2025 for o3).
Most recent knowledge
Choose Claude Sonnet 5.5
Claude Sonnet 5.5 was trained on data up to June 2026, against June 2024 for o3.
Monthly cost at three volumes
| Volume | Claude Sonnet 5.5 | o3 | Difference |
|---|---|---|---|
| Prototype: 1M input, 250K output tokens | $4.50 | $4.00 | o3, $0.50 less |
| Production: 20M input, 5M output tokens | $90.00 | $80.00 | o3, $10.00 less |
| Scale: 500M input, 100M output tokens | $2,000 | $1,800 | o3, $200.00 less |
Standard rates, without caching or batch discounts. Volumes are per month.
Specifications side by side
| Claude Sonnet 5.5 | o3 | |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Category | Language models | Language models |
| Status | Generally available | Legacy |
| Headline price | $4.00 / 1M tokens | $3.50 / 1M tokens |
| Input | $2.00 / 1M tokens | $2.00 / 1M tokens |
| Output | $10.00 / 1M tokens | $8.00 / 1M tokens |
| Cached input | $0.10 / 1M tokens | $0.50 / 1M tokens |
| Context window | 1M | 200k |
| Max output | 128k | 100k |
| Released | September 2026 | Apr 16, 2025 |
| Knowledge cutoff | June 2026 | June 2024 |
| Licence | Proprietary | Proprietary |
| Capabilities | Vision, Reasoning, Tool calling, Structured output, Prompt caching, Batch API | Vision, Reasoning, Tool calling, Structured output, Prompt caching, Batch API |
| API model id | claude-sonnet-5-5 | o3 |
Benchmarks side by side
Leader in bold.
| Benchmark | Claude Sonnet 5.5 | o3 |
|---|---|---|
| Humanity's Last Exam | 55% | 20.1% |
| Long-context reasoning (AA-LCR) | 82.7% | 74.7% |
| Intelligence Index | 56 | No data |
| SciCode | 61% | No data |
| Terminal-Bench Hard | No data | 37.1% |
| GPQA Diamond | No data | 82.7% |
| IFBench (instruction following) | No data | 71.4% |
| τ²-Bench (agentic tool use) | No data | 80.7% |
| MMMU-Pro (visual reasoning) | No data | 70.1% |
Independent evaluations by Artificial Analysis, run the same way for every model, at the reasoning setting shown. Percentages unless marked as an index.
Frequently asked questions
Should I choose Claude Sonnet 5.5 or o3?
Choose Claude Sonnet 5.5 for reused prompts and documents (RAG, agents), very long inputs, reasoning over long documents, the latest release and the most recent knowledge. Choose o3 for high-volume, cost-sensitive work and writing and code generation.
Which is cheaper, Claude Sonnet 5.5 or o3?
o3 is 13% cheaper than Claude Sonnet 5.5 at the headline price ($3.50 / 1M tokens vs $4.00 / 1M tokens).
Which has the larger context window, Claude Sonnet 5.5 or o3?
Claude Sonnet 5.5 reads more per request: 1M tokens against 200k.
What is the difference between Claude Sonnet 5.5 and o3?
Claude Sonnet 5.5 is made by Anthropic and o3 by OpenAI. o3 is 13% cheaper than Claude Sonnet 5.5 at the headline price ($3.50 / 1M tokens vs $4.00 / 1M tokens). Claude Sonnet 5.5 reads more per request: 1M tokens against 200k. Claude Sonnet 5.5 is the newer model (September 2026, against Apr 16, 2025).
How much do Claude Sonnet 5.5 and o3 cost per month?
At 20 million input and 5 million output tokens a month, Claude Sonnet 5.5 costs $90.00 and o3 costs $80.00, at standard rates.
Which is newer, Claude Sonnet 5.5 or o3?
Claude Sonnet 5.5 was released on September 2026 and o3 on Apr 16, 2025.