Pick Grok Code Fast 1 for fast, cheap agentic coding at $0.20/$1.50 or low-latency code generation and terminal 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.
Grok Code Fast 1 (xAI) and Mercury 2.5 Preview (Inception Labs) are two of the models people most often weigh against each other in 2026. Grok Code Fast 1 is xAI's speed-tier coding model at $0.20/$1.50 with a 256K window — cheap, fast agentic code over frontier quality. 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 5× cheaper on input ($0.04/$0.15 per 1M tokens vs $0.2/$1.5 per 1M tokens) — a large enough gap that at scale it can be the single biggest line item in the decision.
Context window: 256K vs 260K tokens — within a few percent of each other, so treat this as a tie and test on your own long inputs, since usable recall varies by model.
Recency: Mercury 2.5 Preview is the newer model by about 12 months (released August 31, 2026), usually meaning fresher training data and capabilities.
Specifications
Spec
Grok Code Fast 1
Mercury 2.5 Preview
Provider
xAI (US)
Inception Labs (US)
Released
August 28, 2025
August 31, 2026
Context window
256K (~384 pages)
260K tokens (~390 pages)
Price (in/out)
$0.2/$1.5 per 1M tokens
$0.04/$0.15 per 1M tokens
Open weight?
No — API only
No — API only
Modalities
text, code
text
SWE-Bench Verified
Not published
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
Fast, cheap agentic coding at $0.20/$1.50: Grok Code Fast 1 — Grok Code Fast 1 lists fast, cheap agentic coding at $0.20/$1.50 among its strengths; Mercury 2.5 Preview does not.
Low-latency code generation and terminal tasks: Grok Code Fast 1 — Grok Code Fast 1 lists low-latency code generation and terminal tasks among its strengths; Mercury 2.5 Preview does not.
High-volume coding pipelines where speed beats peak quality: Grok Code Fast 1 — Grok Code Fast 1 lists high-volume coding pipelines where speed beats peak quality 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 Grok Code Fast 1 ($0.2/$1.5 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.
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 Grok Code Fast 1, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases: Mercury 2.5 Preview — Larger 260K tokens window fits more in one prompt.
Anyone whose priority is fast, cheap agentic coding at $0.20/$1.50: Grok Code Fast 1 — 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.
Grok Code Fast 1: where it fits
XAI's speed-tier coding model at $0.20/$1.50 with a 256K window — cheap, fast agentic code over frontier quality. Released August 28, 2025 by xAI, it is built for fast, cheap agentic coding at $0.20/$1.50, low-latency code generation and terminal tasks, high-volume coding pipelines where speed beats peak quality, and a 256K window sized for real codebases.
Its trade-offs are real: text and code only — no image, audio or video input, xAI did not publish a SWE-Bench Verified score, a speed-tier coding model, not a frontier reasoner, and narrow focus — built for code, not general knowledge work. At $0.2 in / $1.5 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
Grok Code Fast 1 and Mercury 2.5 Preview overlap enough that the right pick depends on your specific job. Mercury 2.5 Preview costs less per token; Mercury 2.5 Preview holds the larger context; and each leads in its own area — Grok Code Fast 1 for fast, cheap agentic coding at $0.20/$1.50, 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 Grok Code Fast 1 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, Grok Code Fast 1 leans toward fast, cheap agentic coding at $0.20/$1.50 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, Grok Code Fast 1 or Mercury 2.5 Preview?
Mercury 2.5 Preview is cheaper — $0.2/$1.5 per 1M tokens vs $0.04/$0.15 per 1M tokens, roughly 5× apart on input.
Which has the bigger context window?
Effectively neither — 256K vs 260K tokens is a difference of a few percent. Remember advertised ≠ usable: recall typically degrades before the ceiling.
Can I use both Grok Code Fast 1 and Mercury 2.5 Preview together?
Yes — a multi-model platform like LumiChats gives you Grok Code Fast 1, 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, Grok Code Fast 1 or Mercury 2.5 Preview?
Mercury 2.5 Preview — released August 31, 2026, about 12 months after Grok Code Fast 1.
Grok Code Fast 1 vs Mercury 2.5 Preview
xAI · US | Inception Labs · US · Updated June 2026
Quick verdict
Pick Grok Code Fast 1 for fast, cheap agentic coding at $0.20/$1.50 or low-latency code generation and terminal 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.
Grok Code Fast 1 (xAI) and Mercury 2.5 Preview (Inception Labs) are two of the models people most often weigh against each other in 2026. Grok Code Fast 1 is xAI's speed-tier coding model at $0.20/$1.50 with a 256K window — cheap, fast agentic code over frontier quality. 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 5× cheaper on input ($0.04/$0.15 per 1M tokens vs $0.2/$1.5 per 1M tokens) — a large enough gap that at scale it can be the single biggest line item in the decision.
▸Context window: 256K vs 260K tokens — within a few percent of each other, so treat this as a tie and test on your own long inputs, since usable recall varies by model.
▸Recency: Mercury 2.5 Preview is the newer model by about 12 months (released August 31, 2026), usually meaning fresher training data and capabilities.
Side-by-side specs
Spec
Grok Code Fast 1
Mercury 2.5 Preview
Provider
xAI (US)
Inception Labs (US)
Released
August 28, 2025
August 31, 2026
Context window
256K (~384 pages)
260K tokens (~390 pages)
Price (in/out)
$0.2/$1.5 per 1M tokens
$0.04/$0.15 per 1M tokens
Open weight?
No — API only
No — API only
Modalities
text, code
text
SWE-Bench Verified
Not published
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
Fast, cheap agentic coding at $0.20/$1.50
Grok Code Fast 1
Grok Code Fast 1 lists fast, cheap agentic coding at $0.20/$1.50 among its strengths; Mercury 2.5 Preview does not.
Low-latency code generation and terminal tasks
Grok Code Fast 1
Grok Code Fast 1 lists low-latency code generation and terminal tasks among its strengths; Mercury 2.5 Preview does not.
High-volume coding pipelines where speed beats peak quality
Grok Code Fast 1
Grok Code Fast 1 lists high-volume coding pipelines where speed beats peak quality 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 Grok Code Fast 1 ($0.2/$1.5 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.
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 Grok Code Fast 1, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases
→ Mercury 2.5 Preview
Larger 260K tokens window fits more in one prompt.
Anyone whose priority is fast, cheap agentic coding at $0.20/$1.50
→ Grok Code Fast 1
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.
Grok Code Fast 1: where it fits
XAI's speed-tier coding model at $0.20/$1.50 with a 256K window — cheap, fast agentic code over frontier quality. Released August 28, 2025 by xAI, it is built for fast, cheap agentic coding at $0.20/$1.50, low-latency code generation and terminal tasks, high-volume coding pipelines where speed beats peak quality, and a 256K window sized for real codebases.
Its trade-offs are real: text and code only — no image, audio or video input, xAI did not publish a SWE-Bench Verified score, a speed-tier coding model, not a frontier reasoner, and narrow focus — built for code, not general knowledge work. At $0.2 in / $1.5 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
Grok Code Fast 1 and Mercury 2.5 Preview overlap enough that the right pick depends on your specific job. Mercury 2.5 Preview costs less per token; Mercury 2.5 Preview holds the larger context; and each leads in its own area — Grok Code Fast 1 for fast, cheap agentic coding at $0.20/$1.50, 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 Grok Code Fast 1 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 Grok Code Fast 1 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, Grok Code Fast 1 leans toward fast, cheap agentic coding at $0.20/$1.50 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, Grok Code Fast 1 or Mercury 2.5 Preview?
Mercury 2.5 Preview is cheaper — $0.2/$1.5 per 1M tokens vs $0.04/$0.15 per 1M tokens, roughly 5× apart on input.
Which has the bigger context window?
Effectively neither — 256K vs 260K tokens is a difference of a few percent. Remember advertised ≠ usable: recall typically degrades before the ceiling.
Can I use both Grok Code Fast 1 and Mercury 2.5 Preview together?
Yes — a multi-model platform like LumiChats gives you Grok Code Fast 1, 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, Grok Code Fast 1 or Mercury 2.5 Preview?
Mercury 2.5 Preview — released August 31, 2026, about 12 months after Grok Code Fast 1.
Specifications and benchmarks reflect publicly reported figures as of June 2026 and may change as providers release updates. Always verify on your own workload.