GPT-5 mini vs GPT OSS 120B (Fireworks): API Cost Comparison
Compare the API pricing, context windows, features, and real-world cost projections for GPT-5 mini (OpenAI) and GPT OSS 120B (Fireworks) (Fireworks AI). Use the interactive calculator below to compute your exact monthly cost based on your token usage and request volume.
Prices verified Mar 10, 2026
Interactive Cost Calculator
Fills in typical token counts for a workload type
Tokens in each prompt sent to the model
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Showing costs for 2 models. Cheapest: GPT OSS 120B (Fireworks) at $4.50/month.
| Alert | |||||||
|---|---|---|---|---|---|---|---|
BestGPT OSS 120B (Fireworks) | Fireworks AI | $4.50 | $0.000450 | $1.50 | $3.00 | 64.0% | Alerts coming soon |
GPT-5 mini | OpenAI | $12.50 | $0.001250 | $2.50 | $10.00 | — | Alerts coming soon |
Monthly Cost Comparison
Price Comparison at a Glance
All prices are in USD per 1 million tokens ($/M tokens). Lower is cheaper.
| Pricing Type | GPT-5 mini | GPT OSS 120B (Fireworks) | Cheaper |
|---|---|---|---|
| Input (standard) | $0.25/M | $0.15/M | GPT OSS 120B (Fireworks) |
| Output | $2.00/M | $0.60/M | GPT OSS 120B (Fireworks) |
| Cached input | $0.03/M | $0.08/M | GPT-5 mini |
| Batch input | N/A | $0.08/M | — |
| Batch output | N/A | $0.30/M | — |
Prices last verified: 2026-03-08 – 2026-03-10
Cost Breakdown by Usage Volume
Estimated monthly costs at different request volumes, assuming 1,000 input tokens and 500 output tokens per request. Adjust in the calculator above for your specific use case.
| Volume | GPT-5 miniMonthly | GPT OSS 120B (Fireworks)Monthly | GPT-5 miniPer request | GPT OSS 120B (Fireworks)Per request |
|---|---|---|---|---|
| 1K requests/mo | $1.25 | $0.45 | $0.001250 | $0.000450 |
| 10K requests/mo | $12.50 | $4.50 | $0.001250 | $0.000450 |
| 100K requests/mo | $125.00 | $45.00 | $0.001250 | $0.000450 |
| 1M requests/mo | $1,250.00 | $450.00 | $0.001250 | $0.000450 |
Green values indicate the lower-cost option at each volume tier. Cost per request is calculated at 1,000 input + 500 output tokens using standard (non-batch, non-cached) pricing.
Price History
Input price per 1M tokensWhen to Choose GPT-5 mini
by OpenAI
- Customer support
- General chatbot
- Data extraction
Input / 1M tokens
$0.25/M
Output / 1M tokens
$2.00/M
Context window
400,000
Tier
mid
When to Choose GPT OSS 120B (Fireworks)
by Fireworks AI
- Code generation
- Document summarization
- RAG / Semantic search
Input / 1M tokens
$0.15/M
Output / 1M tokens
$0.60/M
Context window
131,072
Tier
mid
Key Differences Beyond Price
Cost is only one factor in choosing an AI model. Context window size, rate limits, supported features, and latency all affect whether a model fits your use case.
| Capability | GPT-5 mini | GPT OSS 120B (Fireworks) |
|---|---|---|
| Context window | 400,000 tokens | 131,072 tokens |
| Max output tokens | 128,000 tokens | 16,384 tokens |
| Performance tier | Mid | Mid |
| Vision / image input | Yes | No |
| Function calling | Yes | Yes |
| JSON mode | Yes | Yes |
| Prompt caching | Yes | Yes |
| Batch API (50% discount) | No | Yes |
| Extended reasoning | No | No |
| Fine-tuning | No | No |
| Rate limit (req/min) | 10,000 | Not published |
GPT-5 mini notes
1M context window at mid-tier pricing. Good balance of cost and capability.
GPT OSS 120B (Fireworks) notes
Fireworks serverless pricing. Cached input 50% discount. Batch at 50% of serverless.
Frequently Asked Questions
Is GPT-5 mini cheaper than GPT OSS 120B (Fireworks)?
At standard usage (1,000 input tokens, 500 output tokens, 100,000 requests/month), GPT OSS 120B (Fireworks) costs $45.00/month versus $125.00/month for GPT-5 mini — a 64% saving. Your actual savings will vary based on your token profile; output-heavy workloads amplify differences in output pricing.
Which model has a larger context window, GPT-5 mini or GPT OSS 120B (Fireworks)?
GPT-5 mini has a larger context window at 400,000 tokens, compared to 131,072 tokens for GPT OSS 120B (Fireworks). A larger context window is important for processing long documents, multi-turn conversations, or large codebases without truncation.
Do GPT-5 mini and GPT OSS 120B (Fireworks) support the Batch API?
GPT OSS 120B (Fireworks) supports the Batch API (50% discount for async processing), while GPT-5 mini does not. If your workload tolerates up to 24-hour latency, routing to GPT OSS 120B (Fireworks) with batch pricing could significantly cut costs versus GPT-5 mini's standard rate.
Which model offers better prompt caching?
Both GPT-5 mini and GPT OSS 120B (Fireworks) support prompt caching. GPT-5 mini caches repeated input at $0.03/M (vs $0.25/M standard), while GPT OSS 120B (Fireworks) caches at $0.08/M (vs $0.15/M standard). For workloads with large, repeated system prompts or document context, caching can reduce effective input costs by 60–90%.
What are the best use cases for GPT-5 mini vs GPT OSS 120B (Fireworks)?
GPT-5 mini is best suited for Customer support, General chatbot, Data extraction, while GPT OSS 120B (Fireworks) is optimized for Code generation, Document summarization, RAG / Semantic search. Choose based on which use case matches your primary workload — and validate with the cost calculator above to confirm the total monthly spend fits your budget.
What is the cost per request for GPT-5 mini vs GPT OSS 120B (Fireworks)?
At 1,000 input tokens and 500 output tokens per request — a typical conversational workload — GPT-5 mini costs $0.001250 per request and GPT OSS 120B (Fireworks) costs $0.000450 per request. At 100,000 requests/month, that translates to $125.00 and $45.00 respectively. Use the interactive calculator to adjust these parameters for your actual workload.
GPT-5 mini vs GPT OSS 120B (Fireworks): Summary
When comparing GPT-5 mini and GPT OSS 120B (Fireworks) for API cost, the right choice depends on your workload's token profile, required features, and tolerance for latency. GPT OSS 120B (Fireworks) offers lower total cost at standard usage volumes (1,000 input + 500 output tokens per request at 100,000 requests/month) at $45.00/month, compared to $125.00/month for GPT-5 mini.
Both models are priced in USD per million tokens, the standard unit across all major AI API providers. GPT-5 mini charges $0.25/M for input tokens and $2.00/M for output tokens. GPT OSS 120B (Fireworks) charges $0.15/M input and $0.60/M output. If your workload is output-heavy (more tokens generated than consumed as input), the model with the lower output price compounds cost savings significantly at scale.
Prompt caching is supported by both models. For workloads with large, repeated system prompts or document context — such as RAG pipelines or multi-turn conversations with a fixed knowledge base — prompt caching can reduce effective input costs by 60–90%, which may change the cost ranking between these two models at your specific usage pattern.
Context window capacity differs between the two: GPT-5 mini supports up to 400,000 tokens in a single request, versus 131,072 tokens for GPT OSS 120B (Fireworks). A larger context window is essential for document summarization, large codebase analysis, and multi-document retrieval-augmented generation (RAG) applications.
Use the interactive calculator at the top of this page to enter your actual token usage and monthly request volume for a precise cost comparison tailored to your workload. Adjust for batch API discounts and prompt caching to find the most cost-effective option for your specific deployment.
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Relevant Use Cases
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