Llama 3.1 405B vs GPT-5 Nano: Detailed Comparison
Choosing between Llama 3.1 405B (Meta) and
GPT-5 Nano (OpenAI) comes down to three things:
per-token pricing, context window, and which capability matters most for your workload.
Llama 3.1 405B costs $3.50/M input vs
$0.05/M for GPT-5 Nano;
context windows are 128K vs
400K tokens. Detailed breakdown below.
Side-by-side specs
| Spec | Llama 3.1 405B | GPT-5 Nano |
|---|
| Provider | Meta | OpenAI |
|---|
| Released | 2024-07-23 | 2025-08-07 |
|---|
| Input price |
$3.50/M |
$0.05/M |
| Output price |
$3.50/M |
$0.40/M |
| Cached input |
— |
$0.0050/M |
| Context window |
128K |
400K |
| Max output |
4K |
64K |
| Modalities |
text |
text |
| Tokenizer |
llama-3 |
o200k_base |
Capability matrix
| Capability | Llama 3.1 405B | GPT-5 Nano |
|---|
| function calling |
Yes |
Yes |
| json mode |
Yes |
Yes |
| streaming |
Yes |
Yes |
Per-call cost on typical workloads
| Workload (in/out tokens) | Llama 3.1 405B | GPT-5 Nano | Cheaper by |
|---|
| Standard chat (1K / 500) |
$0.005250 |
$0.000250 |
GPT-5 Nano by $0.005000 |
| RAG (4K / 500) |
$0.015750 |
$0.000400 |
GPT-5 Nano by $0.015350 |
| Long doc (20K / 1K) |
$0.073500 |
$0.001400 |
GPT-5 Nano by $0.072100 |
| Very long context (100K / 2K) |
$0.355250 |
$0.005600 |
GPT-5 Nano by $0.349650 |
When to choose Llama 3.1 405B over GPT-5 Nano
- Llama 3.1 405B fits when your stack is already on Meta (single billing, SDK, observability surface).
When to choose GPT-5 Nano over Llama 3.1 405B
- Per-token input cost is 99% lower than Llama 3.1 405B.
- Larger context window (400K vs 128K).
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