Claude Sonnet 5 vs OpenAI o3
OpenAI o3 is cheaper for every workload modelled here.
List prices checked
Specifications and rates
| Property | Claude Sonnet 5 | OpenAI o3 |
|---|---|---|
| Input per 1M | $3.00 | $2.00 |
| Output per 1M | $15.00 | $8.00 |
| Cached input per 1M | $0.300 | $0.500 |
| Blended (3:1) | $6.00 | $3.50 |
| Context window | 200K | 200K |
| Max output | 64K | 100K |
| Inputs accepted | text, image | text, image |
Source: Anthropic pricing (August 2026) · OpenAI pricing (May 2026). Published list prices only — committed-use discounts, regional variation, and per-request charges are not included. Not yet independently re-checked against the vendor’s page.
Monthly cost by workload
Identical token volumes through both rate cards. Output-heavy profiles are where the ranking flips.
| Workload | Claude Sonnet 5 | OpenAI o3 | Cheaper |
|---|---|---|---|
| In-app chat assistantA support or help assistant handling a few thousand conversations a month, with short prompts and short answers. | $135 | $80 | OpenAI o3saves $55/mo (41%) |
| RAG over documentsRetrieval-augmented answering where each request stuffs several retrieved passages into the prompt, so input dominates. | $1,125 | $720 | OpenAI o3saves $405/mo (36%) |
| Coding agentAn agentic loop that reads files and writes patches, generating heavy output and re-sending large context on every turn. | $2,700 | $1,600 | OpenAI o3saves $1,100/mo (41%) |
What each one is for
Claude Sonnet 5
by Anthropic
The workhorse of the Claude family and the default for production work at volume. Introductory pricing of $2/$10 per million tokens runs to 31 August 2026; the $3/$15 standard rate shown here is what applies after that.
OpenAI o3
by OpenAI
A reasoning model that spends tokens thinking before answering. The list price understates the real cost, because reasoning tokens bill as output and can dominate the total.
Common questions
- Is Claude Sonnet 5 or OpenAI o3 cheaper in 2026?
- OpenAI o3, for every workload modelled here. On a blended 3:1 basis it costs $3.50 per million tokens against Claude Sonnet 5's $6.00.
- Which has the larger context window?
- Both accept 200K tokens.
- Which is cheaper for output-heavy work like agents?
- OpenAI o3, at $8.00 per million output tokens against $15.00. Reasoning tokens bill as output, so for agentic loops this axis usually decides the invoice regardless of what the input rates look like.
- What is not included in these figures?
- Batch-processing discounts, fine-tuning, long-context surcharges above a provider's standard tier, and any enterprise agreement. These are published pay-as-you-go list prices, checked against each provider's own pricing page on the date shown.
- Is switching from Claude Sonnet 5 to OpenAI o3 worth it?
- On price alone it is about 42% cheaper on a blended basis. Whether that survives contact with your workload depends on output quality and on retry rate — a cheaper model that needs two attempts is not cheaper. Model the specific volumes in the calculator before you migrate.