GPT-5.3-Codex vs GPT-5.5
How do these models stack up? Below is an expert side-by-side comparison of specifications, context window capacity, live pricing per million tokens, and standardized benchmark scores for GPT-5.3-Codex and GPT-5.5.
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...
GPT-5.5
GPT-5.5 is OpenAI’s frontier model designed for complex professional workloads, building on GPT-5.4 with stronger reasoning, higher reliability, and improved token efficiency on hard tasks. It features a 1M+ token...
Technical Specifications
| Specification | GPT-5.3-Codex | GPT-5.5 |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Context Window | 400,000 tokens | 1,050,000 tokens |
| Agent Suitability | N/A | 95/100 |
| Time to First Token (TTFT) | N/A | 380 ms |
| Deployment Model | managed api | managed api |
| Production Stability | stable | stable |
| API Available | Yes | Yes |
| Released Date | 2026-02-24 | 2026-04-24 |
API Pricing Comparison
Input Price per Million Tokens
GPT-5.3-Codex
$1.75
GPT-5.5
$5.00
Output Price per Million Tokens
GPT-5.3-Codex
$14.00
GPT-5.5
$30.00
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Benchmark Performance Metrics
Scores show the raw performance percentages verified across key evaluation suites. Higher bars indicate superior accuracy and capability in that domain.
GPT-5.3-Codex Quirks & Gotchas
No developer gotchas reported.
GPT-5.5 Quirks & Gotchas
- ▸Best for JSON schema adherence — strict mode available via response_format parameter
- ▸Requires explicit tool_choice for deterministic function calling