Model detail
GPT-5.3-Codex
GPT-5.3-Codex is OpenAI’s most advanced agentic coding model, combining the frontier software engineering performance of GPT-5.2-Codex with the broader reasoning and professional knowledge capabilities of GPT-5.2. It achieves state-of-the-art results on SWE-Bench Pro and strong performance on Terminal-Bench 2.0 and OSWorld-Verified, reflecting improved multi-language coding, terminal proficiency, and real-world computer-use skills. The model is optimized for long-running, tool-using workflows and supports interactive steering during execution, making it suitable for complex development tasks, debugging, deployment, and iterative product work. Beyond coding, GPT-5.3-Codex performs strongly on structured knowledge-work benchmarks such as GDPval, supporting tasks like document drafting, spreadsheet analysis, slide creation, and operational research across domains. It is trained with enhanced cybersecurity awareness, including vulnerability identification capabilities, and deployed with additional safeguards for high-risk use cases. Compared to prior Codex models, it is more token-efficient and approximately 25% faster, targeting professional end-to-end workflows that span reasoning, execution, and computer interaction.
Model specs
- Model ID
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gpt-5.3-codex
- Context length
- 400K
- Max output
- 128K
- I/O modalities
- Released
- 2026-02
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API endpoints
One MixRoute gateway, OpenAI-compatible
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OpenAI-compatible
/v1/chat/completionsPOST
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Pricing
Flat rate, unit: /1M Tokens
Input
$1.7500 /1M Tokens
Completion
$14.0000 /1M Tokens
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Selection summary
Quickly judge whether it fits your workload
What is this model good for?
Codex model for coding and agentic tasks
GPT-5.3-Codex: GPT-5.3-Codex is optimized for agentic coding tasks in Codex or similar environments. GPT-5.3-Codex supports low, medium, high, and xhigh reasoning effort settings. If you want to . 400,000-token context.
What should you check before using it?
400,000 context, 128,000 output
OpenAI model. Supports tool calling, structured outputs, function calling. Knowledge cutoff: 2025-08-31.
Why use it through MixRoute?
Drop-in via OpenAI-compatible endpoint on MixRoute
Set the model parameter to "gpt-5.3-codex" and use your MixRoute API key.
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Capabilities & compatibility
Unconfirmed capabilities stay "Unknown," no guesses
Tool calling
GPT-5.3-Codex supports function and tool calls.
tools definition; the response returns tool_calls to execute and feed results back.
Structured output
GPT-5.3-Codex can produce JSON-formatted output on demand.
response_format: { type: "json_schema" } forces valid JSON output.
Streaming
GPT-5.3-Codex supports streamed responses.
stream: true streams tokens incrementally, so chat UIs render as they arrive.
Prompt caching
GPT-5.3-Codex supports prompt caching under supported routing conditions.
Vision input
GPT-5.3-Codex can process image inputs alongside text.
image_url content part alongside text messages.
OpenAI SDK
Call GPT-5.3-Codex through MixRoute's OpenAI-compatible endpoint.
base_url to https://api.mixroute.ai/v1; everything else follows the OpenAI style.
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Token cost estimator
Live estimate from this page's pricing, not an actual bill
This model has no cache-read price; caching is not counted
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FAQ
gpt-5.3-codex supports up to 128000 output tokens per request. Plan your prompts to stay within this limit, and use the max_tokens or max_completion_tokens parameter to control output length.
One endpoint, a testable decision
Test this model and alternate routes with the same request format
Start from a real workload, then let quality, total cost, and failure conditions decide whether to send production traffic.