Llama 3.1 405B vs Phi-3 Small 128K
Llama 3.1 405B (2024) and Phi-3 Small 128K (2024) are compact production models from AI at Meta and Microsoft Research. Llama 3.1 405B ships a 128K-token context window, while Phi-3 Small 128K ships a 128K-token context window. On Google-Proof Q&A, Phi-3 Small 128K leads by a hair. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit. It focuses on practical selection signals rather than broad model-family marketing.
Llama 3.1 405B is safer overall; choose Phi-3 Small 128K when provider fit matters.
Specs
| Specification | ||
|---|---|---|
| Released | 2024-07-23 | 2024-05-21 |
| Context window | 128K | 128K |
| Parameters | 405B | 7B |
| Architecture | decoder only | decoder only |
| License | Open Source | Open Source |
| Knowledge cutoff | - | - |
Pricing and availability
| Pricing attribute | Llama 3.1 405B | Phi-3 Small 128K |
|---|---|---|
| Input price | - | $0.35/1M tokens |
| Output price | - | $1.05/1M tokens |
| Providers | - |
Capabilities
| Capability | Llama 3.1 405B | Phi-3 Small 128K |
|---|---|---|
| Vision | No | No |
| Multimodal | No | No |
| Reasoning | No | No |
| Function calling | No | No |
| Tool use | No | No |
| Structured outputs | No | No |
| Code execution | No | No |
Benchmarks
| Benchmark | Llama 3.1 405B | Phi-3 Small 128K |
|---|---|---|
| Google-Proof Q&A | 51.5 | 51.9 |
| HumanEval | 89.0 | 73.8 |
| Massive Multitask Language Understanding | 88.6 | 78.1 |
| HellaSwag | 95.8 | 90.8 |
Deep dive
On shared benchmark coverage, Google-Proof Q&A has Llama 3.1 405B at 51.5 and Phi-3 Small 128K at 51.9, with Phi-3 Small 128K ahead by 0.4 points; HumanEval has Llama 3.1 405B at 89 and Phi-3 Small 128K at 73.8, with Llama 3.1 405B ahead by 15.2 points; Massive Multitask Language Understanding has Llama 3.1 405B at 88.6 and Phi-3 Small 128K at 78.1, with Llama 3.1 405B ahead by 10.5 points. The largest visible gap is 15.2 points on HumanEval, which matters most when that benchmark mirrors your workload. Treat isolated benchmark wins as directional, because provider routing, prompt style, and tool access can move real application results.
The capability footprint is close: both models cover the core production surface. That makes context budget, benchmark fit, and provider maturity more important than a simple checklist. If your application depends on one integration detail, verify it against the provider route you plan to use, not just the base model listing.
Pricing coverage is uneven: Llama 3.1 405B has no token price sourced yet and Phi-3 Small 128K has $0.35/1M input tokens. Provider availability is 0 tracked routes versus 2. Treat unknown pricing as an integration gap, then verify the route you will actually call before estimating production spend.
Choose Llama 3.1 405B when provider fit are central to the workload. Choose Phi-3 Small 128K 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.
FAQ
Which has a larger context window, Llama 3.1 405B or Phi-3 Small 128K?
Llama 3.1 405B supports 128K tokens, while Phi-3 Small 128K supports 128K tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Is Llama 3.1 405B or Phi-3 Small 128K open source?
Llama 3.1 405B is listed under Open Source. Phi-3 Small 128K 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.
Where can I run Llama 3.1 405B and Phi-3 Small 128K?
Llama 3.1 405B is available on the tracked providers still being sourced. Phi-3 Small 128K is available on Microsoft Foundry and NVIDIA NIM. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
When should I pick Llama 3.1 405B over Phi-3 Small 128K?
Llama 3.1 405B is safer overall; choose Phi-3 Small 128K when provider fit matters. If your workload also depends on provider fit, start with Llama 3.1 405B; if it depends on provider fit, run the same evaluation with Phi-3 Small 128K.
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Last reviewed: 2026-05-01. Data sourced from public model cards and provider documentation.