GPT-5.6 Luna vs Grok 4.5
OpenAI · US | xAI · US · Updated June 2026
Quick verdict
Pick GPT-5.6 Luna for cheapest gpt-5.6 tier for high-volume drafting and automation or fast, affordable execution while keeping respectable coding. Pick Grok 4.5 for cheap, token-efficient agentic coding — about gpt-5.5-codex quality at roughly half the cost or extreme token efficiency — around 4x fewer output tokens per task than opus 4.8. On a tight budget at scale, GPT-5.6 Luna is the value pick.
GPT-5.6 Luna (OpenAI) and Grok 4.5 (xAI) are two of the models people most often weigh against each other in 2026. GPT-5.6 Luna is the budget, high-throughput GPT-5.6 tier — built for cheap, fast, large-volume work rather than deep long-context reasoning. Grok 4.5 is xAI's first coding-focused model — pitched as Opus-class but faster, more token-efficient, and cheaper, undercutting GPT-5.5-Codex. They diverge most on price and context window — each quantified below from the models' real specs.
Key differences at a glance
- ▸Price: GPT-5.6 Luna is about 2× cheaper on input ($1/$6 per 1M tokens vs $2/$6 per 1M tokens) — meaningful once you are processing millions of tokens a month.
- ▸Context window: GPT-5.6 Luna holds 2× more — 1M (~1,500 pages) vs 500K (~750 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
Side-by-side specs
| Spec | GPT-5.6 Luna | Grok 4.5 |
|---|---|---|
| Provider | OpenAI (US) | xAI (US) |
| Released | July 9, 2026 | July 8, 2026 |
| Context window | 1M (~1,500 pages) | 500K (~750 pages) |
| Price (in/out) | $1/$6 per 1M tokens | $2/$6 per 1M tokens |
| Open weight? | No — API only | No — API only |
| Modalities | text, image, code | text, image, code |
| SWE-Bench Verified | Not published | Not published |
| MRCR v2 @ 1M | Not published | Not published |
Who wins what
Cheapest GPT-5.6 tier for high-volume drafting and automation
GPT-5.6 Luna
At $1/$6 per 1M tokens it undercuts Grok 4.5 ($2/$6 per 1M tokens), and that gap compounds at volume.
Fast, affordable execution while keeping respectable coding
GPT-5.6 Luna
The budget, high-throughput GPT-5.6 tier — built for cheap, fast, large-volume work rather than deep long-context reasoning — and it runs cheaper at $1/$6 per 1M tokens.
Same 1M context and programmatic tool calling as its siblings
GPT-5.6 Luna
Its 1M window holds about 2× more than Grok 4.5's 500K in a single prompt.
Cheap, token-efficient agentic coding — about GPT-5.5-Codex quality at roughly half the cost
Grok 4.5
Grok 4.5 lists cheap, token-efficient agentic coding — about GPT-5.5-Codex quality at roughly half the cost among its strengths; GPT-5.6 Luna does not.
Extreme token efficiency — around 4x fewer output tokens per task than Opus 4.8
Grok 4.5
Grok 4.5 lists extreme token efficiency — around 4x fewer output tokens per task than Opus 4.8 among its strengths; GPT-5.6 Luna does not.
In-IDE coding, trained on real Cursor developer sessions and shipped natively in Cursor
Grok 4.5
Grok 4.5 lists in-IDE coding, trained on real Cursor developer sessions and shipped natively in Cursor among its strengths; GPT-5.6 Luna does not.
Lowest cost at scale
GPT-5.6 Luna
At $1/$6 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Largest single-prompt input
GPT-5.6 Luna
Its 1M window is about 2× larger than Grok 4.5's 500K, fitting roughly 1,500 pages in one prompt.
Which should you pick?
A cost-sensitive startup shipping high volume
→ GPT-5.6 Luna
At $1/$6 per 1M tokens it undercuts Grok 4.5, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases
→ GPT-5.6 Luna
Larger 1M window fits more in one prompt.
Anyone whose priority is cheapest gpt-5.6 tier for high-volume drafting and automation
→ GPT-5.6 Luna
It is specifically built for that.
Anyone whose priority is cheap, token-efficient agentic coding — about gpt-5.5-codex quality at roughly half the cost
→ Grok 4.5
That is its strongest area.
GPT-5.6 Luna: where it fits
The budget, high-throughput GPT-5.6 tier — built for cheap, fast, large-volume work rather than deep long-context reasoning. Released July 9, 2026 by OpenAI, it is built for cheapest GPT-5.6 tier for high-volume drafting and automation, fast, affordable execution while keeping respectable coding, same 1M context and programmatic tool calling as its siblings, and high-throughput simple agentic jobs.
Its trade-offs are real: weak long-context recall deep in its 1M window (MRCR far below Sol), and lowest raw capability of the three GPT-5.6 tiers; no open weights. At $1 in / $6 out per million tokens, it sits in the budget price band.
Grok 4.5: where it fits
XAI's first coding-focused model — pitched as Opus-class but faster, more token-efficient, and cheaper, undercutting GPT-5.5-Codex. Released July 8, 2026 by xAI, it is built for cheap, token-efficient agentic coding — about GPT-5.5-Codex quality at roughly half the cost, extreme token efficiency — around 4x fewer output tokens per task than Opus 4.8, in-IDE coding, trained on real Cursor developer sessions and shipped natively in Cursor, and top-tier placement on the Artificial Analysis Intelligence Index.
Its trade-offs: smaller 500K context (halved from the 1M generation), with pricing that doubles above 200K tokens, and eU launch delayed; no open weights. At $2 in / $6 out per million tokens, it sits in the mid price band.
The bottom line for this matchup
GPT-5.6 Luna and Grok 4.5 overlap enough that the right pick depends on your specific job. GPT-5.6 Luna costs less per token; GPT-5.6 Luna holds the larger context; and each leads in its own area — GPT-5.6 Luna for cheapest gpt-5.6 tier for high-volume drafting and automation, Grok 4.5 for cheap, token-efficient agentic coding — about gpt-5.5-codex quality at roughly half the cost. Rather than crowning one, run the same hard task through both once and let the results decide.
Want both GPT-5.6 Luna and Grok 4.5 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.
See pricingFrequently asked questions
Is GPT-5.6 Luna or Grok 4.5 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-5.6 Luna leans toward cheapest gpt-5.6 tier for high-volume drafting and automation while Grok 4.5 leans toward cheap, token-efficient agentic coding — about gpt-5.5-codex quality at roughly half the cost, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, GPT-5.6 Luna or Grok 4.5?
GPT-5.6 Luna is cheaper — $1/$6 per 1M tokens vs $2/$6 per 1M tokens, roughly 2× apart on input.
Which has the bigger context window?
GPT-5.6 Luna — 1M vs 500K, about 2× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both GPT-5.6 Luna and Grok 4.5 together?
Yes — a multi-model platform like LumiChats gives you GPT-5.6 Luna, Grok 4.5 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-5.6 Luna or Grok 4.5?
GPT-5.6 Luna — released July 9, 2026, about 1 days after Grok 4.5.
Related comparisons
Specifications and benchmarks reflect publicly reported figures as of June 2026 and may change as providers release updates. Always verify on your own workload.