LFM2.5-1.2B-Instruct (free) is free for input tokens while GPT-5.1 Chat costs $1.25 per 1M tokens.
API cost decision in 10 seconds
LFM2.5-1.2B-Instruct (free) vs GPT-5.1 Chat
Pick LFM2.5-1.2B-Instruct (free) for lower cost; pick GPT-5.1 Chat only if the larger context window matters more.
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Data confirmed:
Prices normalized to USD per 1M tokens
Sample workload: 1M input + 500K output
Budget verdict
Pick LFM2.5-1.2B-Instruct (free) for lower cost; pick GPT-5.1 Chat only if the larger context window matters more.
On the standard 1M input plus 500K output workload, LFM2.5-1.2B-Instruct (free) is estimated at $0 vs $6.25 for GPT-5.1 Chat, saving $6.25 (100% lower).
Cost-first pickLFM2.5-1.2B-Instruct (free)
Context-first pickGPT-5.1 Chat
Sample savings$6.25100%
10x traffic gap$62.5
GPT-5.1 Chat has more context, but LFM2.5-1.2B-Instruct (free) saves $6.25 on the standard workload. At 10x that traffic, the same price gap is about $62.5. Use the calculator below to replace the sample workload with your own token volume.
Cost sensitivity
Workload Sensitivity
LFM2.5-1.2B-Instruct (free) stays cheaper across input-heavy, balanced, and output-heavy sample workloads.
| Workload shape | Token mix | Better pick | LFM2.5-1.2B-Instruct (free) | GPT-5.1 Chat |
|---|---|---|---|---|
| Input-heavy / RAG | 5M input + 500K output | LFM2.5-1.2B-Instruct (free) | $0 | $11.25 |
| Balanced workload | 1M input + 1M output | LFM2.5-1.2B-Instruct (free) | $0 | $11.25 |
| Output-heavy chatbot | 1M input + 5M output | LFM2.5-1.2B-Instruct (free) | $0 | $51.25 |
LFM2.5-1.2B-Instruct (free) is free for output tokens while GPT-5.1 Chat costs $10 per 1M tokens.
GPT-5.1 Chat has 95.23K more context (3.91x larger).
LFM2.5-1.2B-Instruct (free) is free for the standard workload while the other model is estimated at $6.25.
Estimate your workload cost
Your Workload Cost
This estimate uses normalized public API pricing per 1M tokens. It is a planning aid, not a billing quote. Verify provider pricing, limits, and terms before production use.
Quick Decision
LFM2.5-1.2B-Instruct (free) has the lower input price; LFM2.5-1.2B-Instruct (free) has the lower output price; GPT-5.1 Chat offers the larger context window. For the 1M input plus 500K output sample, LFM2.5-1.2B-Instruct (free) is cheaper for the standard workload.
For a 1M input token plus 500K output token workload, the estimated API cost is $0 for LFM2.5-1.2B-Instruct (free) and $6.25 for GPT-5.1 Chat.
Choose LFM2.5-1.2B-Instruct (free) when you care most about lower input-token price, and lower output-token price.
Choose GPT-5.1 Chat when you care most about larger context window.
- On the standard 1M input plus 500K output workload, LFM2.5-1.2B-Instruct (free) is estimated at $0 vs $6.25 for GPT-5.1 Chat, saving $6.25 (100% lower).
- LFM2.5-1.2B-Instruct (free) is free for the standard workload while the other model is estimated at $6.25.
- LFM2.5-1.2B-Instruct (free) is free for input tokens while GPT-5.1 Chat costs $1.25 per 1M tokens.
- LFM2.5-1.2B-Instruct (free) is free for output tokens while GPT-5.1 Chat costs $10 per 1M tokens.
- GPT-5.1 Chat has 95.23K more context (3.91x larger).
| Feature | LFM2.5-1.2B-Instruct (free) (LiquidAI) | GPT-5.1 Chat (OpenAI) |
|---|---|---|
| Input Price prompt tokens per 1M | $0 | $1.25 |
| Completion Price per 1M tokens | $0 | $10 |
| Sample Workload Cost 1M input + 500K output | $0 | $6.25 |
| Context Window | 32.77K | 128K |
| Release Date |
Use-Case Decision Matrix
| Use case | Better pick | Why |
|---|---|---|
| Budget-constrained production | LFM2.5-1.2B-Instruct (free) | On the standard 1M input plus 500K output workload, LFM2.5-1.2B-Instruct (free) is estimated at $0 vs $6.25 for GPT-5.1 Chat, saving $6.25 (100% lower). |
| High-volume input processing | LFM2.5-1.2B-Instruct (free) | Lower prompt-token price matters most when prompts, retrieved passages, or documents dominate the bill. |
| Long responses and chatbots | LFM2.5-1.2B-Instruct (free) | Lower output-token price matters most when assistants generate many completion tokens. |
| RAG or long-document work | GPT-5.1 Chat | A larger context window leaves more room for retrieved passages, conversation history, or source files. |
Related Alternatives
- gpt-oss-120b (free) can replace GPT-5.1 Chat when lower sample workload cost matters most: $0.
- gpt-oss-20b (free) can replace GPT-5.1 Chat when lower sample workload cost matters most: $0.
- gpt-oss-20b can replace GPT-5.1 Chat when lower sample workload cost matters most: $0.1.
- gpt-oss-120b can replace GPT-5.1 Chat when lower sample workload cost matters most: $0.13.
- Llama 4 Scout offers 10M context with $0.23 sample workload cost.
- Grok 4.20 Multi-Agent offers 2M context with $5 sample workload cost.
- Grok 4.20 offers 2M context with $2.5 sample workload cost.
- Owl Alpha offers 1.05M context with $0 sample workload cost.
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Open OpenAI modelsLFM2.5-1.2B-Instruct is a compact, high-performance instruction-tuned model built for fast on-device AI. It delivers strong chat quality in a 1.2B parameter footprint, with efficient edge inference and broad runtime support.
GPT-5.1 Chat (AKA Instant is the fast, lightweight member of the 5.1 family, optimized for low-latency chat while retaining strong general intelligence. It uses adaptive reasoning to selectively “think” on...