GPT-5.3-Codex vs Llama 3.1 405B Instruct
GPT-5.3-Codex (2026) and Llama 3.1 405B Instruct (2024) are agentic coding models from OpenAI and AI at Meta. GPT-5.3-Codex ships a not-yet-sourced context window, while Llama 3.1 405B Instruct ships a 128K-token context window. On pricing, GPT-5.3-Codex costs $1.75/1M input tokens versus $2.4/1M 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-5.3-Codex is safer overall; choose Llama 3.1 405B Instruct when provider fit matters.
Specs
| Released | 2026-02-05 | 2024-07-23 |
| Context window | — | 128K |
| Parameters | — | 405B |
| Architecture | decoder only | decoder only |
| License | Proprietary | Open Source |
| Knowledge cutoff | - | - |
Pricing and availability
| GPT-5.3-Codex | Llama 3.1 405B Instruct | |
|---|---|---|
| Input price | $1.75/1M tokens | $2.4/1M tokens |
| Output price | $14/1M tokens | $2.4/1M tokens |
| Providers |
Capabilities
| GPT-5.3-Codex | Llama 3.1 405B Instruct | |
|---|---|---|
| Vision | ||
| Multimodal | ||
| Reasoning | ||
| Function calling | ||
| Tool use | ||
| Structured outputs | ||
| Code execution |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on multimodal input: GPT-5.3-Codex, function calling: GPT-5.3-Codex, tool use: GPT-5.3-Codex, and code execution: GPT-5.3-Codex. Both models share 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 Llama 3.1 405B Instruct lists $2.4/1M input and $2.4/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Llama 3.1 405B Instruct lower by about $3.02 per million blended tokens. Availability is 1 providers versus 11, so concentration risk also matters.
Choose GPT-5.3-Codex when coding workflow support and lower input-token cost are central to the workload. Choose Llama 3.1 405B Instruct when provider fit 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. 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 is cheaper, GPT-5.3-Codex or Llama 3.1 405B Instruct?
GPT-5.3-Codex is cheaper on tracked token pricing. GPT-5.3-Codex costs $1.75/1M input and $14/1M output tokens. Llama 3.1 405B Instruct costs $2.4/1M input and $2.4/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is GPT-5.3-Codex or Llama 3.1 405B Instruct open source?
GPT-5.3-Codex is listed under Proprietary. Llama 3.1 405B Instruct is listed under Open Source. 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 Llama 3.1 405B Instruct?
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 function calling, GPT-5.3-Codex or Llama 3.1 405B Instruct?
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.
Which is better for tool use, GPT-5.3-Codex or Llama 3.1 405B Instruct?
GPT-5.3-Codex has the clearer documented tool use signal in this comparison. If tool use 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 Llama 3.1 405B Instruct?
GPT-5.3-Codex is available on OpenRouter. Llama 3.1 405B Instruct is available on OctoAI API, Together AI, Fireworks AI, IBM watsonx, and Scale AI GenAI Platform. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
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Last reviewed: 2026-04-24. Data sourced from public model cards and provider documentation.