GPT-5.3 Codex
Reasoning model by OpenAI.
OpenAI's specialized reasoning model fine-tuned for agentic software engineering and long-horizon programming tasks in Codex, featuring a 400,000-token context window and up to 128,000 output tokens.
This model is deprecated
GPT-5.3 Codex has been deprecated. It is still served on nRouter and can still be called.
Caller Notice: To help identify integrations still relying on this model, all API responses now include x-nr-model-deprecated: true and Warning: 299 - "Model deprecated" headers.
Specifications
Context window, ranked against other reasoning models
Proportional scale: 0 to 200K tokens. Not ranked, no published context window: gpt-5.2-pro-2025-12-11, gpt-5.4-pro, grok-4-1-fast-non-reasoning, grok-4-1-fast-reasoning, gpt-5.2-pro.
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reasoning
Pricing
Rates are read live
Pricing for gpt-5.3-codex is fetched from the live catalogue on load, so it is never served from a cache that could outlive a repricing.
Availability
Not enough data yet
We have not collected enough health probes for this model to publish an uptime or latency figure. A percentage from a handful of samples is fabricated precision, so none is shown until the sample count supports one.
How GPT-5.3 Codex is billed
Billed at the provider's list price, with no per-token markup.
- Exact list price
- Tokens settle at the published rate of the model that served your call.
- Cache discounts passed through
- Provider prompt-caching discounts reach your balance with no added fee.
- Cost on every response
- Each response carries the
x-nr-request-costheader, so you can reconcile spend per request.
More from OpenAI
Start building with gpt-5.3-codex
One API key, three steps. Choose your tool to begin.
Get a key
Create API keySet your API key
export NROUTER_API_KEY="<YOUR_API_KEY>"Configure Claude Code
Choose a tool, then copy its setup from the panel.
FAQs
What is GPT-5.3 Codex?
OpenAI's specialized reasoning model fine-tuned for agentic software engineering and long-horizon programming tasks in Codex, featuring a 400,000-token context window and up to 128,000 output tokens.
How much does GPT-5.3 Codex cost?
GPT-5.3 Codex is billed at the provider's list price on nRouter with no per-token markup — tokens settle at the exact upstream rate. Input and output rates are read live, so see the pricing section above for the current figures.
Does GPT-5.3 Codex support tool calling and structured outputs?
Yes. GPT-5.3 Codex supports tool calling (function calling), so it can invoke external tools and APIs during a conversation.
What inputs and outputs does GPT-5.3 Codex support?
GPT-5.3 Codex takes text and images as input and returns text as output.
How do I use GPT-5.3 Codex via nRouter?
Use any OpenAI-compatible client: point it at https://api.nrouter.ai/v1 with your nRouter API key and set the model to "openai/gpt-5.3-codex". The quick-start panel above has a copy-paste curl command for this model.
When was GPT-5.3 Codex released?
GPT-5.3 Codex was released on February 24, 2026.
Where is the GPT-5.3 Codex documentation?
Start at nrouter.ai/docs. The quick-start guide (nrouter.ai/docs/getting-started/quick-start) covers API keys and your first request, and the API reference (nrouter.ai/docs/api-reference) lists every parameter.
What other text models does OpenAI have?
Other OpenAI text models on nRouter include GPT-OSS 120B 1 (nrouter.ai/models/gpt-oss-120b-1), GPT-6.1 Sol (nrouter.ai/models/gpt-6.1-sol), GPT-5.2 Pro (nrouter.ai/models/gpt-5.2-pro-2025-12-11), GPT Audio 1.5 (nrouter.ai/models/gpt-audio-1.5).