GPT-5.3-Codex vs GPT-5.5 Instant
GPT-5.3-Codex (2026) and GPT-5.5 Instant (2026) are agentic coding models from OpenAI. GPT-5.3-Codex ships a 400K-token context window, while GPT-5.5 Instant ships a 400K-token context window. On pricing, GPT-5.5 Instant costs $1.5/1M 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.
GPT-5.5 Instant is safer overall; choose GPT-5.3-Codex when coding workflow support matters.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-02-05 | 2026-05-05 |
| Context window | 400K | 400K |
| Parameters | — | — |
| Architecture | decoder only | decoder only |
| License | Proprietary | Proprietary |
| Knowledge cutoff | 2025-08 | 2025-08 |
Pricing and availability
| Pricing attribute | GPT-5.3-Codex | GPT-5.5 Instant |
|---|---|---|
| Input price | $1.75/1M tokens | $1.5/1M tokens |
| Output price | $14/1M tokens | $6/1M tokens |
| Providers |
Capabilities
| Capability | GPT-5.3-Codex | GPT-5.5 Instant |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | No | Yes |
| Reasoning | Yes | No |
| Function calling | Yes | Yes |
| Tool use | Yes | Yes |
| Structured outputs | Yes | Yes |
| Code execution | Yes | Yes |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on multimodal input: GPT-5.5 Instant and reasoning mode: GPT-5.3-Codex. Both models share vision, function calling, tool use, and structured outputs, 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 GPT-5.5 Instant lists $1.5/1M input and $6/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts GPT-5.5 Instant lower by about $2.58 per million blended tokens. Availability is 2 providers versus 1, so concentration risk also matters.
Choose GPT-5.3-Codex when coding workflow support and broader provider choice are central to the workload. Choose GPT-5.5 Instant when coding workflow support and lower input-token cost are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship. This keeps the decision grounded in measurable tradeoffs instead of brand-level assumptions. It also helps separate model capability from provider packaging, which can change cost and latency.
FAQ
Which has a larger context window, GPT-5.3-Codex or GPT-5.5 Instant?
GPT-5.3-Codex supports 400K tokens, while GPT-5.5 Instant supports 400K tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Which is cheaper, GPT-5.3-Codex or GPT-5.5 Instant?
GPT-5.5 Instant is cheaper on tracked token pricing. GPT-5.3-Codex costs $1.75/1M input and $14/1M output tokens. GPT-5.5 Instant costs $1.5/1M input and $6/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is GPT-5.3-Codex or GPT-5.5 Instant open source?
GPT-5.3-Codex is listed under Proprietary. GPT-5.5 Instant is listed under Proprietary. 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 vision, GPT-5.3-Codex or GPT-5.5 Instant?
Both GPT-5.3-Codex and GPT-5.5 Instant expose vision. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Which is better for multimodal input, GPT-5.3-Codex or GPT-5.5 Instant?
GPT-5.5 Instant 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.
Where can I run GPT-5.3-Codex and GPT-5.5 Instant?
GPT-5.3-Codex is available on OpenRouter and OpenAI API. GPT-5.5 Instant is available on OpenAI 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.
Continue comparing
Last reviewed: 2026-05-11. Data sourced from public model cards and provider documentation.