API cost decision in 10 seconds

GPT-5.5 Pro vs Mercury 2

Pick Mercury 2 for lower cost; pick GPT-5.5 Pro only if the larger context window matters more.

Page updated: 2026-05-26T10:03:26Z Data confirmed: 2026-05-26T12:43:06Z Prices normalized to USD per 1M tokens Sample workload: 1M input + 500K output

Budget verdict

Pick Mercury 2 for lower cost; pick GPT-5.5 Pro only if the larger context window matters more.

On the standard 1M input plus 500K output workload, Mercury 2 is estimated at $0.62 vs $120 for GPT-5.5 Pro, saving $119.38 (99.5% lower).

Cost-first pickMercury 2

Context-first pickGPT-5.5 Pro

Sample savings$119.3899.5%

10x traffic gap$1193.75

GPT-5.5 Pro has more context, but Mercury 2 saves $119.38 on the standard workload. At 10x that traffic, the same price gap is about $1193.75. Use the calculator below to replace the sample workload with your own token volume.

Cost sensitivity

Workload Sensitivity

Same prices, different token mixes.

Mercury 2 stays cheaper across input-heavy, balanced, and output-heavy sample workloads.

Workload shape	Token mix	Better pick	GPT-5.5 Pro	Mercury 2
Input-heavy / RAG	5M input + 500K output	Mercury 2	$240	$1.62
Balanced workload	1M input + 1M output	Mercury 2	$210	$1
Output-heavy chatbot	1M input + 5M output	Mercury 2	$930	$4

Cheaper input Mercury 2 $30 vs $0.25 / 1M

Mercury 2 is $29.75 cheaper per 1M input tokens (99.2% lower; 120x difference).

Cheaper output Mercury 2 $180 vs $0.75 / 1M

Mercury 2 is $179.25 cheaper per 1M output tokens (99.6% lower; 240x difference).

Larger context GPT-5.5 Pro 1.05M vs 128K

GPT-5.5 Pro has 922K more context (8.2x larger).

Sample workload Mercury 2 $120 vs $0.62

Mercury 2 is $119.38 cheaper on the standard workload (99.5% lower).

Estimate your workload cost

Your Workload Cost

Prices are normalized to USD per 1M tokens.

Monthly input tokens Monthly output tokens

GPT-5.5 Pro Calculating… Estimated API cost

Mercury 2 Calculating… Estimated API cost

Cheaper for this workload Calculating… Difference: calculating…

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

Verdict

Mercury 2 has the lower input price; Mercury 2 has the lower output price; GPT-5.5 Pro offers the larger context window. For the 1M input plus 500K output sample, Mercury 2 is cheaper for the standard workload.

For a 1M input token plus 500K output token workload, the estimated API cost is $120 for GPT-5.5 Pro and $0.62 for Mercury 2.

Best Fit

Choose GPT-5.5 Pro when you care most about larger context window.

Choose Mercury 2 when you care most about lower input-token price, and lower output-token price.

Decision Notes

On the standard 1M input plus 500K output workload, Mercury 2 is estimated at $0.62 vs $120 for GPT-5.5 Pro, saving $119.38 (99.5% lower).
Mercury 2 is $119.38 cheaper on the standard workload (99.5% lower).
Mercury 2 is $29.75 cheaper per 1M input tokens (99.2% lower; 120x difference).
Mercury 2 is $179.25 cheaper per 1M output tokens (99.6% lower; 240x difference).
GPT-5.5 Pro has 922K more context (8.2x larger).

Head-to-Head Specs

Feature	GPT-5.5 Pro (OpenAI)	Mercury 2 (Inception)
Input Price prompt tokens per 1M	$30	$0.25
Completion Price per 1M tokens	$180	$0.75
Sample Workload Cost 1M input + 500K output	$120	$0.62
Context Window	1.05M	128K
Release Date	2026-04-24	2026-03-04

Use-Case Decision Matrix

Use case	Better pick	Why
Budget-constrained production	Mercury 2	On the standard 1M input plus 500K output workload, Mercury 2 is estimated at $0.62 vs $120 for GPT-5.5 Pro, saving $119.38 (99.5% lower).
High-volume input processing	Mercury 2	Lower prompt-token price matters most when prompts, retrieved passages, or documents dominate the bill.
Long responses and chatbots	Mercury 2	Lower output-token price matters most when assistants generate many completion tokens.
RAG or long-document work	GPT-5.5 Pro	A larger context window leaves more room for retrieved passages, conversation history, or source files.

Related Alternatives

Same-provider lower-cost swaps

gpt-oss-120b (free) can replace GPT-5.5 Pro when lower sample workload cost matters most: $0.
gpt-oss-20b (free) can replace GPT-5.5 Pro when lower sample workload cost matters most: $0.
gpt-oss-20b can replace GPT-5.5 Pro when lower sample workload cost matters most: $0.1.
gpt-oss-120b can replace GPT-5.5 Pro when lower sample workload cost matters most: $0.13.

Larger context near this budget

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.

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OpenAI catalog

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Inception catalog

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Open Inception models

GPT-5.5 Pro

GPT-5.5 Pro is OpenAI’s high-capability model optimized for deep reasoning and accuracy on complex, high-stakes workloads. It features a 1M+ token context window (922K input, 128K output) with support for...

Mercury 2

Mercury 2 is an extremely fast reasoning LLM, and the first reasoning diffusion LLM (dLLM). Instead of generating tokens sequentially, Mercury 2 produces and refines multiple tokens in parallel, achieving...