GPT-5.5 Instant vs Llama 3.1 405B Instruct
GPT-5.5 Instant (2026) and Llama 3.1 405B Instruct (2024) are compact production models from OpenAI and AI at Meta. GPT-5.5 Instant ships a 400k-token context window, while Llama 3.1 405B Instruct ships a 128k-token context window. On pricing, Llama 3.1 405B Instruct costs $2.40/1M input tokens versus $5/1M for the alternative. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.
Llama 3.1 405B Instruct is ~108% cheaper at $2.40/1M; pay for GPT-5.5 Instant only for coding workflow support.
Decision scorecard
Local evidence first| Signal | GPT-5.5 Instant | Llama 3.1 405B Instruct |
|---|---|---|
| Best for | multimodal apps and tool-calling agents | provider-routed production |
| Decision fit | Coding, RAG, and Agents | RAG, Long context, and Classification |
| Context window | 400k | 128k |
| Cheapest output | $30/1M tokens | $2.40/1M tokens |
| Provider routes | 1 tracked | 11 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- GPT-5.5 Instant has the larger context window for long prompts, retrieval packs, or transcript analysis.
- GPT-5.5 Instant uniquely exposes Vision, Multimodal, and Function calling in local model data.
- Local decision data tags GPT-5.5 Instant for Coding, RAG, and Agents.
- 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 procurement 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.
GPT-5.5 Instant
$11,500
Cheapest tracked route/tier: OpenAI API
Llama 3.1 405B Instruct
$2,520
Cheapest tracked route/tier: AWS Bedrock
Estimated monthly gap: $8,980. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- No overlapping tracked provider route is sourced for GPT-5.5 Instant and Llama 3.1 405B Instruct; plan for SDK, billing, or endpoint changes.
- Llama 3.1 405B Instruct is $27.60/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Vision, Multimodal, and Function calling before moving production traffic.
- No overlapping tracked provider route is sourced for Llama 3.1 405B Instruct and GPT-5.5 Instant; plan for SDK, billing, or endpoint changes.
- GPT-5.5 Instant is $27.60/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- GPT-5.5 Instant adds Vision, Multimodal, and Function calling in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-05-05 | 2024-07-23 |
| Context window | 400k | 128k |
| Parameters | — | 405B |
| Architecture | decoder only | decoder only |
| License | Proprietary | Llama 3 Community |
| Openness | Proprietary | Open weights |
| Commercial use | Commercial use with conditions | Commercial use with conditions |
| Knowledge cutoff | 2025-08 | 2023-12 |
Pricing and availability
| Pricing attribute | GPT-5.5 Instant | Llama 3.1 405B Instruct |
|---|---|---|
| Input price | $5/1M tokens | $2.40/1M tokens |
| Output price | $30/1M tokens | $2.40/1M tokens |
| Providers |
Capabilities
| Capability | GPT-5.5 Instant | Llama 3.1 405B Instruct |
|---|---|---|
| Vision | Yes | No |
| Multimodal | Yes | No |
| Reasoning | No | No |
| Function calling | Yes | No |
| Tool use | Yes | No |
| Structured outputs | Yes | Yes |
| Code execution | Yes | No |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on vision: GPT-5.5 Instant, multimodal input: GPT-5.5 Instant, function calling: GPT-5.5 Instant, tool use: GPT-5.5 Instant, and code execution: GPT-5.5 Instant. 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-5.5 Instant lists $5/1M input and $30/1M output tokens on the cheapest tracked provider, while Llama 3.1 405B Instruct lists $2.40/1M input and $2.40/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Llama 3.1 405B Instruct lower by about $10.10 per million blended tokens. Availability is 1 providers versus 11, so concentration risk also matters.
Choose GPT-5.5 Instant when coding workflow support and larger context windows are central to the workload. Choose Llama 3.1 405B Instruct when provider fit, lower input-token cost, 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.
FAQ
Which has a larger context window, GPT-5.5 Instant or Llama 3.1 405B Instruct?
GPT-5.5 Instant supports 400k tokens, while Llama 3.1 405B Instruct supports 128k tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Which is cheaper, GPT-5.5 Instant or Llama 3.1 405B Instruct?
Llama 3.1 405B Instruct is cheaper on tracked token pricing. GPT-5.5 Instant costs $5/1M input and $30/1M output tokens. Llama 3.1 405B Instruct costs $2.40/1M input and $2.40/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is GPT-5.5 Instant or Llama 3.1 405B Instruct open source?
GPT-5.5 Instant is listed under Proprietary. Llama 3.1 405B Instruct is listed under Llama 3 Community. 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 vision, GPT-5.5 Instant or Llama 3.1 405B Instruct?
GPT-5.5 Instant has the clearer documented vision signal in this comparison. If vision is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Which is better for multimodal input, GPT-5.5 Instant or Llama 3.1 405B Instruct?
GPT-5.5 Instant 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.
Where can I run GPT-5.5 Instant and Llama 3.1 405B Instruct?
GPT-5.5 Instant is available on OpenAI API. Llama 3.1 405B Instruct is available on OctoAI API (Deprecated), 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: 2026-05-19. Data sourced from public model cards and provider documentation.