GPT-5.3-Codex vs o3
GPT-5.3-Codex (2026) and o3 (2025) are agentic coding models from OpenAI. GPT-5.3-Codex ships a not-yet-sourced context window, while o3 ships a 128K-token context window. On SWE-bench Verified, GPT-5.3-Codex leads by 13.3 pts. On pricing, o3 costs $1/1M input tokens versus $1.75/1M for the alternative. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit. It focuses on practical selection signals rather than broad model-family marketing.
o3 is ~75% cheaper at $1/1M; pay for GPT-5.3-Codex only for coding workflow support.
Specs
| Released | 2026-02-05 | 2025-03-31 |
| Context window | — | 128K |
| Parameters | — | — |
| Architecture | decoder only | decoder only |
| License | Proprietary | Unknown |
| Knowledge cutoff | - | - |
Pricing and availability
| GPT-5.3-Codex | o3 | |
|---|---|---|
| Input price | $1.75/1M tokens | $1/1M tokens |
| Output price | $14/1M tokens | $4/1M tokens |
| Providers |
Capabilities
| GPT-5.3-Codex | o3 | |
|---|---|---|
| Vision | ||
| Multimodal | ||
| Reasoning | ||
| Function calling | ||
| Tool use | ||
| Structured outputs | ||
| Code execution |
Benchmarks
| Benchmark | GPT-5.3-Codex | o3 |
|---|---|---|
| SWE-bench Verified | 85.0 | 71.7 |
Deep dive
On shared benchmark coverage, SWE-bench Verified has GPT-5.3-Codex at 85 and o3 at 71.7, with GPT-5.3-Codex ahead by 13.3 points. The largest visible gap is 13.3 points on SWE-bench Verified, which matters most when that benchmark mirrors your workload. Treat isolated benchmark wins as directional, because provider routing, prompt style, and tool access can move real application results.
The capability footprint differs most on multimodal input: GPT-5.3-Codex, reasoning mode: o3, function calling: GPT-5.3-Codex, and tool use: GPT-5.3-Codex. Both models share structured outputs and code execution, so the practical split is not just feature count. Use those differences to decide whether the page is about raw model quality, agentic coding support, multimodal ingestion, or predictable structured API behavior.
For cost, GPT-5.3-Codex lists $1.75/1M input and $14/1M output tokens, while o3 lists $1/1M input and $4/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts o3 lower by about $3.52 per million blended tokens. Availability is 1 providers versus 3, so concentration risk also matters.
Choose GPT-5.3-Codex when coding workflow support are central to the workload. Choose o3 when coding workflow support, lower input-token cost, and broader provider choice are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship.
FAQ
Which is cheaper, GPT-5.3-Codex or o3?
o3 is cheaper on tracked token pricing. GPT-5.3-Codex costs $1.75/1M input and $14/1M output tokens. o3 costs $1/1M input and $4/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is GPT-5.3-Codex or o3 open source?
GPT-5.3-Codex is listed under Proprietary. o3 is listed under Unknown. License labels affect whether you can self-host, redistribute weights, or rely only on hosted APIs, so confirm the upstream license before deployment.
Which is better for multimodal input, GPT-5.3-Codex or o3?
GPT-5.3-Codex has the clearer documented multimodal input signal in this comparison. If multimodal input is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Which is better for reasoning mode, GPT-5.3-Codex or o3?
o3 has the clearer documented reasoning mode signal in this comparison. If reasoning mode is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Which is better for function calling, GPT-5.3-Codex or o3?
GPT-5.3-Codex has the clearer documented function calling signal in this comparison. If function calling is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run GPT-5.3-Codex and o3?
GPT-5.3-Codex is available on OpenRouter. o3 is available on OpenAI API, OpenRouter, and OpenAI Batch API. Provider coverage can affect latency, region availability, compliance posture, and fallback options. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
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Last reviewed: 2026-04-24. Data sourced from public model cards and provider documentation.