GPT-5.3-Codex vs Llama 3.1 405B Instruct

GPT-5.3-Codex (2026) and Llama 3.1 405B Instruct (2024) compare a coding-specialized model against a standalone API model. GPT-5.3-Codex ships a 400k-token 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 $2.40/1M for the alternative. This page treats the result as workflow and deployment fit, not a universal model winner.

Treat this as a product-type comparison: GPT-5.3-Codex is coding-specialized model, while Llama 3.1 405B Instruct is standalone API model. Choose based on workflow fit before reading any benchmark or price row as decisive.

Decision scorecard

Local evidence first

Signal	GPT-5.3-Codex	Llama 3.1 405B Instruct	How to read it
Product type	Coding-specialized model	Standalone API model	Read downstream rows through the product-type lens before comparing benchmarks, prices, or provider availability.
Best for	custom coding agents, code generation, and tool loops	provider-routed production	Use-case synthesis from product type, capability flags, context, and provider data.
Decision fit	Coding, RAG, and Agents	RAG, Long context, and Classification	Primary workload tags from local decision data.
Context window	400k	128k	Higher is better when prompts, retrieval chunks, or transcripts are large.
Cheapest output	$14/1M tokens	$2.40/1M tokens	Cheapest tracked provider route; verify your exact region and tier.
Provider routes	3 tracked	11 tracked	Broader coverage can reduce vendor lock-in and fallback risk.
Shared benchmarks	0 shared	0 shared	No shared benchmark scores are available for this pair yet.

Decision tradeoffs

Choose GPT-5.3-Codex when...

GPT-5.3-Codex has the larger context window for long prompts, retrieval packs, or transcript analysis.
GPT-5.3-Codex uniquely exposes Vision, Reasoning, and JSON / Tool use in local model data.
Local decision data tags GPT-5.3-Codex for Coding, RAG, and Agents.

Choose Llama 3.1 405B Instruct when...

Llama 3.1 405B Instruct has the lower cheapest tracked output price at $2.40/1M tokens.
Llama 3.1 405B Instruct has broader tracked provider coverage for fallback and route flexibility.
Local decision data tags Llama 3.1 405B Instruct for RAG, Long context, and Classification.

Monthly cost at traffic

Estimate token spend from the cheapest tracked input and output route or tier on this page.

Lower estimate Llama 3.1 405B Instruct

Requests / monthInput tokens / requestOutput tokens / request

GPT-5.3-Codex

$4,900

Cheapest tracked route/tier: OpenRouter

Llama 3.1 405B Instruct

$2,520

Cheapest tracked route/tier: AWS Bedrock

Estimated monthly gap: $2,380. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.

Switch friction

GPT-5.3-Codex -> Llama 3.1 405B Instruct

No overlapping tracked provider route is sourced for GPT-5.3-Codex and Llama 3.1 405B Instruct; plan for SDK, billing, or endpoint changes.
Llama 3.1 405B Instruct is $11.60/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
Check replacement coverage for Vision, Reasoning, and JSON / Tool use before moving production traffic.

Llama 3.1 405B Instruct -> GPT-5.3-Codex

No overlapping tracked provider route is sourced for Llama 3.1 405B Instruct and GPT-5.3-Codex; plan for SDK, billing, or endpoint changes.
GPT-5.3-Codex is $11.60/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
GPT-5.3-Codex adds Vision, Reasoning, and JSON / Tool use in local capability data.

Specs

Specification	GPT-5.3-Codex OpenAI	Llama 3.1 405B Instruct AI at Meta
Released	2026-02-05	2024-07-23
Context window	400k	128k
Parameters	—	405B
Architecture	Decoder Only	Decoder Only
License	Proprietary	Llama 3 Community
Openness	Proprietary	Open weights
Weights	Not released	Available
Code	Unknown	Unknown
Commercial use	Commercial use: conditional	Commercial use: conditional
Knowledge cutoff	2025-08	2023-12

Pricing and availability

Pricing attribute	GPT-5.3-Codex	Llama 3.1 405B Instruct
Input price	$1.75/1M tokens	$2.40/1M tokens
Output price	$14/1M tokens	$2.40/1M tokens
Providers	OpenRouter OpenAI API Vercel AI Gateway	OctoAI API (Deprecated)Together AI Fireworks AI IBM watsonx Scale AI GenAI Platform NVIDIA NIM

Capabilities

Capability	GPT-5.3-Codex	Llama 3.1 405B Instruct
Vision	Yes	No
Multimodal	No	No
Reasoning	Yes	No
JSON / Tool use	Yes	No
Structured outputs	Yes	Yes
Code execution	Yes	No
IDE integration	No	No
Computer use	Yes	No
Parallel agents	No	No

Benchmarks

No shared benchmark scores are currently available for this pair.

Continue comparing

Model pages

Labs and families

Related comparisons

Popular comparisons for GPT-5.3-Codex

Popular comparisons for Llama 3.1 405B Instruct

Last reviewed: 2026-07-11. Data sourced from public model cards and provider documentation.

Both models

GPT-5.3-Codex Llama 3.1 405B Instruct