Pick GPT-5.4 Mini for free for every chatgpt user or fast, low-cost general tasks. Pick Mercury 2.5 Preview for very high inference throughput (1,107 tok/s) via diffusion-based parallel token generation or coding accuracy (95.7%, 91st percentile among cost-optimized models). On a tight budget at scale, Mercury 2.5 Preview is the value pick.
GPT-5.4 Mini (OpenAI) and Mercury 2.5 Preview (Inception Labs) are two of the models people most often weigh against each other in 2026. GPT-5.4 Mini is openAI's free, fast workhorse — capable general AI with no subscription needed. Mercury 2.5 Preview is inception Labs' August 31, 2026 diffusion-based language model preview, refining tokens in parallel for roughly 10x the throughput of comparable autoregressive models at cost-optimized-tier quality. They diverge most on price and context window — each quantified below from the models' real specs.
Key differences
Price: Mercury 2.5 Preview is about 19× cheaper on input ($0.04/$0.15 per 1M tokens vs $0.75/$4.5 per 1M tokens) — a large enough gap that at scale it can be the single biggest line item in the decision.
Context window: GPT-5.4 Mini holds 1.5× more — 400K (~600 pages) vs 260K tokens (~390 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
Recency: Mercury 2.5 Preview is the newer model by about 6 months (released August 31, 2026), usually meaning fresher training data and capabilities.
Specifications
Spec
GPT-5.4 Mini
Mercury 2.5 Preview
Provider
OpenAI (US)
Inception Labs (US)
Released
March 17, 2026
August 31, 2026
Context window
400K (~600 pages)
260K tokens (~390 pages)
Price (in/out)
$0.75/$4.5 per 1M tokens
$0.04/$0.15 per 1M tokens
Open weight?
No — API only
No — API only
Modalities
text, image, code
text
SWE-Bench Verified
Not published
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
Free for every ChatGPT user: GPT-5.4 Mini — OpenAI's free, fast workhorse — capable general AI with no subscription needed — and it carries the larger 400K context.
Fast, low-cost general tasks: GPT-5.4 Mini — GPT-5.4 Mini lists fast, low-cost general tasks among its strengths; Mercury 2.5 Preview does not.
Subagent capabilities: GPT-5.4 Mini — GPT-5.4 Mini lists subagent capabilities among its strengths; Mercury 2.5 Preview does not.
Very high inference throughput (1,107 tok/s) via diffusion-based parallel token generation: Mercury 2.5 Preview — Inception Labs' August 31, 2026 diffusion-based language model preview, refining tokens in parallel for roughly 10x the throughput of comparable autoregressive models at cost-optimized-tier quality — and it runs cheaper at $0.04/$0.15 per 1M tokens.
Coding accuracy (95.7%, 91st percentile among cost-optimized models): Mercury 2.5 Preview — At $0.04/$0.15 per 1M tokens it undercuts GPT-5.4 Mini ($0.75/$4.5 per 1M tokens), and that gap compounds at volume.
Mathematics accuracy (97.0%, 97th percentile): Mercury 2.5 Preview — Inception Labs' August 31, 2026 diffusion-based language model preview, refining tokens in parallel for roughly 10x the throughput of comparable autoregressive models at cost-optimized-tier quality — and it is the newer of the two.
Lowest cost at scale: Mercury 2.5 Preview — At $0.04/$0.15 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Largest single-prompt input: GPT-5.4 Mini — Its 400K window is about 1.5× larger than Mercury 2.5 Preview's 260K tokens, fitting roughly 600 pages in one prompt.
Which should you pick?
A cost-sensitive startup shipping high volume: Mercury 2.5 Preview — At $0.04/$0.15 per 1M tokens it undercuts GPT-5.4 Mini, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases: GPT-5.4 Mini — Larger 400K window fits more in one prompt.
Anyone whose priority is free for every chatgpt user: GPT-5.4 Mini — It is specifically built for that.
Anyone whose priority is very high inference throughput (1,107 tok/s) via diffusion-based parallel token generation: Mercury 2.5 Preview — That is its strongest area.
GPT-5.4 Mini: where it fits
OpenAI's free, fast workhorse — capable general AI with no subscription needed. Released March 17, 2026 by OpenAI, it is built for free for every ChatGPT user, fast, low-cost general tasks, subagent capabilities, and native multimodal reasoning.
Its trade-offs are real: smaller context than flagship models, and not for the hardest reasoning. At $0.75 in / $4.5 out per million tokens, it sits in the budget price band.
Mercury 2.5 Preview: where it fits
Inception Labs' August 31, 2026 diffusion-based language model preview, refining tokens in parallel for roughly 10x the throughput of comparable autoregressive models at cost-optimized-tier quality. Released August 31, 2026 by Inception Labs, it is built for very high inference throughput (1,107 tok/s) via diffusion-based parallel token generation, coding accuracy (95.7%, 91st percentile among cost-optimized models), mathematics accuracy (97.0%, 97th percentile), and tunable reasoning levels with parallel tool calls and schema-aligned JSON output.
Its trade-offs: 260K context window is far shorter than frontier 1M-token models, no vision or audio modalities, positioned only against cost-optimized models (GPT-5.6 Luna Low, Gemini 3.5 Flash-Lite), not frontier-class, and current $0.04/$0.15 pricing includes a limited-time launch promotion on OpenRouter (list price is $0.20/$0.75, may rise after Sept 8, 2026). At $0.04 in / $0.15 out per million tokens, it sits in the budget price band.
The bottom line for this matchup
GPT-5.4 Mini and Mercury 2.5 Preview overlap enough that the right pick depends on your specific job. Mercury 2.5 Preview costs less per token; GPT-5.4 Mini holds the larger context; and each leads in its own area — GPT-5.4 Mini for free for every chatgpt user, Mercury 2.5 Preview for very high inference throughput (1,107 tok/s) via diffusion-based parallel token generation. Rather than crowning one, run the same hard task through both once and let the results decide.
Frequently asked questions
Is GPT-5.4 Mini or Mercury 2.5 Preview better for coding?
Public SWE-Bench figures are not available for either model, so the honest test is your own repository — run an identical real bug through both. By design, GPT-5.4 Mini leans toward free for every chatgpt user while Mercury 2.5 Preview leans toward very high inference throughput (1,107 tok/s) via diffusion-based parallel token generation, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, GPT-5.4 Mini or Mercury 2.5 Preview?
Mercury 2.5 Preview is cheaper — $0.75/$4.5 per 1M tokens vs $0.04/$0.15 per 1M tokens, roughly 19× apart on input.
Which has the bigger context window?
GPT-5.4 Mini — 400K vs 260K tokens, about 1.5× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both GPT-5.4 Mini and Mercury 2.5 Preview together?
Yes — a multi-model platform like LumiChats gives you GPT-5.4 Mini, Mercury 2.5 Preview and 40+ others under one ₹69/day pass (about $1/day), so you can draft with one and cross-check with the other instead of buying two subscriptions.
Which is newer, GPT-5.4 Mini or Mercury 2.5 Preview?
Mercury 2.5 Preview — released August 31, 2026, about 6 months after GPT-5.4 Mini.
GPT-5.4 Mini vs Mercury 2.5 Preview
OpenAI · US | Inception Labs · US · Updated June 2026
Quick verdict
Pick GPT-5.4 Mini for free for every chatgpt user or fast, low-cost general tasks. Pick Mercury 2.5 Preview for very high inference throughput (1,107 tok/s) via diffusion-based parallel token generation or coding accuracy (95.7%, 91st percentile among cost-optimized models). On a tight budget at scale, Mercury 2.5 Preview is the value pick.
GPT-5.4 Mini (OpenAI) and Mercury 2.5 Preview (Inception Labs) are two of the models people most often weigh against each other in 2026. GPT-5.4 Mini is openAI's free, fast workhorse — capable general AI with no subscription needed. Mercury 2.5 Preview is inception Labs' August 31, 2026 diffusion-based language model preview, refining tokens in parallel for roughly 10x the throughput of comparable autoregressive models at cost-optimized-tier quality. They diverge most on price and context window — each quantified below from the models' real specs.
Key differences at a glance
▸Price: Mercury 2.5 Preview is about 19× cheaper on input ($0.04/$0.15 per 1M tokens vs $0.75/$4.5 per 1M tokens) — a large enough gap that at scale it can be the single biggest line item in the decision.
▸Context window: GPT-5.4 Mini holds 1.5× more — 400K (~600 pages) vs 260K tokens (~390 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
▸Recency: Mercury 2.5 Preview is the newer model by about 6 months (released August 31, 2026), usually meaning fresher training data and capabilities.
Side-by-side specs
Spec
GPT-5.4 Mini
Mercury 2.5 Preview
Provider
OpenAI (US)
Inception Labs (US)
Released
March 17, 2026
August 31, 2026
Context window
400K (~600 pages)
260K tokens (~390 pages)
Price (in/out)
$0.75/$4.5 per 1M tokens
$0.04/$0.15 per 1M tokens
Open weight?
No — API only
No — API only
Modalities
text, image, code
text
SWE-Bench Verified
Not published
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
Free for every ChatGPT user
GPT-5.4 Mini
OpenAI's free, fast workhorse — capable general AI with no subscription needed — and it carries the larger 400K context.
Fast, low-cost general tasks
GPT-5.4 Mini
GPT-5.4 Mini lists fast, low-cost general tasks among its strengths; Mercury 2.5 Preview does not.
Subagent capabilities
GPT-5.4 Mini
GPT-5.4 Mini lists subagent capabilities among its strengths; Mercury 2.5 Preview does not.
Very high inference throughput (1,107 tok/s) via diffusion-based parallel token generation
Mercury 2.5 Preview
Inception Labs' August 31, 2026 diffusion-based language model preview, refining tokens in parallel for roughly 10x the throughput of comparable autoregressive models at cost-optimized-tier quality — and it runs cheaper at $0.04/$0.15 per 1M tokens.
Coding accuracy (95.7%, 91st percentile among cost-optimized models)
Mercury 2.5 Preview
At $0.04/$0.15 per 1M tokens it undercuts GPT-5.4 Mini ($0.75/$4.5 per 1M tokens), and that gap compounds at volume.
Mathematics accuracy (97.0%, 97th percentile)
Mercury 2.5 Preview
Inception Labs' August 31, 2026 diffusion-based language model preview, refining tokens in parallel for roughly 10x the throughput of comparable autoregressive models at cost-optimized-tier quality — and it is the newer of the two.
Lowest cost at scale
Mercury 2.5 Preview
At $0.04/$0.15 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Largest single-prompt input
GPT-5.4 Mini
Its 400K window is about 1.5× larger than Mercury 2.5 Preview's 260K tokens, fitting roughly 600 pages in one prompt.
Which should you pick?
A cost-sensitive startup shipping high volume
→ Mercury 2.5 Preview
At $0.04/$0.15 per 1M tokens it undercuts GPT-5.4 Mini, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases
→ GPT-5.4 Mini
Larger 400K window fits more in one prompt.
Anyone whose priority is free for every chatgpt user
→ GPT-5.4 Mini
It is specifically built for that.
Anyone whose priority is very high inference throughput (1,107 tok/s) via diffusion-based parallel token generation
→ Mercury 2.5 Preview
That is its strongest area.
GPT-5.4 Mini: where it fits
OpenAI's free, fast workhorse — capable general AI with no subscription needed. Released March 17, 2026 by OpenAI, it is built for free for every ChatGPT user, fast, low-cost general tasks, subagent capabilities, and native multimodal reasoning.
Its trade-offs are real: smaller context than flagship models, and not for the hardest reasoning. At $0.75 in / $4.5 out per million tokens, it sits in the budget price band.
Mercury 2.5 Preview: where it fits
Inception Labs' August 31, 2026 diffusion-based language model preview, refining tokens in parallel for roughly 10x the throughput of comparable autoregressive models at cost-optimized-tier quality. Released August 31, 2026 by Inception Labs, it is built for very high inference throughput (1,107 tok/s) via diffusion-based parallel token generation, coding accuracy (95.7%, 91st percentile among cost-optimized models), mathematics accuracy (97.0%, 97th percentile), and tunable reasoning levels with parallel tool calls and schema-aligned JSON output.
Its trade-offs: 260K context window is far shorter than frontier 1M-token models, no vision or audio modalities, positioned only against cost-optimized models (GPT-5.6 Luna Low, Gemini 3.5 Flash-Lite), not frontier-class, and current $0.04/$0.15 pricing includes a limited-time launch promotion on OpenRouter (list price is $0.20/$0.75, may rise after Sept 8, 2026). At $0.04 in / $0.15 out per million tokens, it sits in the budget price band.
The bottom line for this matchup
GPT-5.4 Mini and Mercury 2.5 Preview overlap enough that the right pick depends on your specific job. Mercury 2.5 Preview costs less per token; GPT-5.4 Mini holds the larger context; and each leads in its own area — GPT-5.4 Mini for free for every chatgpt user, Mercury 2.5 Preview for very high inference throughput (1,107 tok/s) via diffusion-based parallel token generation. Rather than crowning one, run the same hard task through both once and let the results decide.
Want both GPT-5.4 Mini and Mercury 2.5 Preview without two subscriptions? LumiChats gives you these plus 40+ models under one ₹69/day pass (about $1/day) — draft with one, cross-check with the other.
Is GPT-5.4 Mini or Mercury 2.5 Preview better for coding?
Public SWE-Bench figures are not available for either model, so the honest test is your own repository — run an identical real bug through both. By design, GPT-5.4 Mini leans toward free for every chatgpt user while Mercury 2.5 Preview leans toward very high inference throughput (1,107 tok/s) via diffusion-based parallel token generation, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, GPT-5.4 Mini or Mercury 2.5 Preview?
Mercury 2.5 Preview is cheaper — $0.75/$4.5 per 1M tokens vs $0.04/$0.15 per 1M tokens, roughly 19× apart on input.
Which has the bigger context window?
GPT-5.4 Mini — 400K vs 260K tokens, about 1.5× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both GPT-5.4 Mini and Mercury 2.5 Preview together?
Yes — a multi-model platform like LumiChats gives you GPT-5.4 Mini, Mercury 2.5 Preview and 40+ others under one ₹69/day pass (about $1/day), so you can draft with one and cross-check with the other instead of buying two subscriptions.
Which is newer, GPT-5.4 Mini or Mercury 2.5 Preview?
Mercury 2.5 Preview — released August 31, 2026, about 6 months after GPT-5.4 Mini.
Specifications and benchmarks reflect publicly reported figures as of June 2026 and may change as providers release updates. Always verify on your own workload.