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Head-to-head comparison

GPT-5.6 Luna vs GLM 5.3 Flash

GPT-5.6 Luna (OpenAI) and GLM 5.3 Flash (Z.ai) compared on the ModelCap Index, API price, context window, provider availability, weight access and every public benchmark board they share. Figures are the same ones shown on the live rankings; nothing here is a hidden score.

Snapshot as of 9 September 2026

As of 9 September 2026, GLM 5.3 Flash holds the stronger ModelCap Index position (#11 vs #25); GLM 5.3 Flash is 4.8× cheaper per output token ($0.25/1M vs $1.20/1M); GLM 5.3 Flash offers the longer context window (1.3M vs 1M tokens); and GLM 5.3 Flash ships open weights.

Which should you choose?

Choose GPT-5.6 Luna if…

  • ModelCap publishes no field on which GPT-5.6 Luna leads GLM 5.3 Flash for this pair.

Choose GLM 5.3 Flash if…

  • you want the stronger overall ModelCap Index position — #11 against #25 (78.7 vs 70.5 points).
  • API cost matters — $0.25/1M output tokens against $1.20/1M, about 4.8× cheaper.
  • your workload is prompt-heavy — input tokens cost $0.075/1M against $0.20/1M.
  • you need the longer context window — 1.3M tokens against 1M.
  • you want to self-host: GLM 5.3 Flash ships open weights while GPT-5.6 Luna is api only.
  • you want provider choice — 26 listed API providers against 3.
  • Arena coding is your yardstick — 1534 against 1497.
  • LMArena Agent is your yardstick — 2.0% against 1.1%.
  • AA Intelligence Index is your yardstick — 41.9 against 37.5.
  • AA Terminal-Bench 2.1 is your yardstick — 84.3% against 80.9%.
  • AA Humanity's Last Exam is your yardstick — 39.9% against 39.5%.
  • you want the more recently listed model — GLM 5.3 Flash was listed 26 August 2026, GPT-5.6 Luna 9 July 2026.

GPT-5.6 Luna vs GLM 5.3 Flash: specs, pricing and context

Specification comparison of GPT-5.6 Luna and GLM 5.3 Flash
FieldGPT-5.6 LunaOpenAIGLM 5.3 FlashZ.ai
ModelCap Index position#25#11
Index score70.578.7
EvidenceMeasuredMeasured
Input price / 1M tokens$0.20$0.075
Output price / 1M tokens$1.20$0.25
Context window1M tokens1.3M tokens
Max output tokens128K131K
API providers listed326
Weight accessAPI onlyOpen weights
Input modalitiesFile, Image, TextText, Image, Video
First listed9 July 202626 August 2026
PublisherOpenAIZ.ai

Evidence: 6 public benchmark observations across 6 boards · 4 public benchmark observations across 4 boards. Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.

Benchmark scores: GPT-5.6 Luna vs GLM 5.3 Flash

Public benchmark boards where GPT-5.6 Luna or GLM 5.3 Flash has a published result
BoardGPT-5.6 LunaGLM 5.3 FlashLeads
Arena codingArena (LMArena)14971489–1505X-High15341517–1551GLM 5.3 Flash
LMArena AgentLMArena1.1%0.0%–2.2%X-High2.0%1.1%–2.9%GLM 5.3 Flash
ARC-AGI-2ARC Prize Foundation59.5%Max—Only one result
ARC-AGI-3ARC Prize Foundation0.2%Max—Only one result
AA Intelligence IndexArtificial Analysis37.5intelligence-index:v4.3:max41.9intelligence-index:v4.3:reasoning-unspecifiedGLM 5.3 Flash
AA Terminal-Bench 2.1Artificial Analysis80.9%terminal-bench:2.1:terminus-2:e2b:pass-at-1:3-repeats:source-model="GPT-5.6 Luna (max)":reasoning=true84.3%terminal-bench:2.1:terminus-2:e2b:pass-at-1:3-repeats:source-model="GLM-5.3-Flash":reasoning=trueGLM 5.3 Flash
AA Humanity's Last ExamArtificial Analysis39.5%hle:may-2025:text-only-2158:no-tools:pass-at-1:source-model="GPT-5.6 Luna (max)":reasoning=true39.9%hle:may-2025:text-only-2158:no-tools:pass-at-1:source-model="GLM-5.3-Flash":reasoning=trueGLM 5.3 Flash
Terminal-Bench 4.0Terminal-Bench (Laude Institute)17.3%14.4%–20.1%Codex · Max—Only one result

Scores are the sources' own published figures for each model's best evaluated configuration; ModelCap never re-runs a benchmark.

Want a different pairing? Open the interactive comparison tool to swap either model for any current ranked language model.

GPT-5.6 Luna vs GLM 5.3 Flash: common questions

Is GPT-5.6 Luna better than GLM 5.3 Flash?

GLM 5.3 Flash ranks higher on the ModelCap Index as of 9 September 2026: #11 against #25. That is a capability ranking built from public benchmark evidence with published uncertainty; whether it is "better" for you also depends on price, context and where you can run it. Their published uncertainty intervals overlap, so the rank difference alone does not establish a reliable capability advantage for your workload.

Is GPT-5.6 Luna cheaper than GLM 5.3 Flash?

GLM 5.3 Flash is cheaper on output tokens: $0.25/1M against $1.20/1M. Input tokens are $0.20/1M for GPT-5.6 Luna and $0.075/1M for GLM 5.3 Flash. Prices are the lowest listed API offer ModelCap observed, in USD per million tokens. For 1,000 requests with 2,000 input and 500 output tokens each (2M input + 0.5M output), the listed-rate estimate is $1.00 for GPT-5.6 Luna versus $0.28 for GLM 5.3 Flash. GLM 5.3 Flash costs 72.5% less in this scenario. This excludes caching, batch discounts, prompt-length tiers, tool charges and retries; verify the selected endpoint before budgeting.

Which has the bigger context window, GPT-5.6 Luna or GLM 5.3 Flash?

GLM 5.3 Flash has the larger context window: 1.3M tokens against 1M.

Which is better for coding, GPT-5.6 Luna or GLM 5.3 Flash?

Arena coding: GPT-5.6 Luna 1497, GLM 5.3 Flash 1534 — GLM 5.3 Flash leads. AA Terminal-Bench 2.1: GPT-5.6 Luna 80.9%, GLM 5.3 Flash 84.3% — GLM 5.3 Flash leads.

Are GPT-5.6 Luna and GLM 5.3 Flash open-weight models?

GPT-5.6 Luna: API only. GLM 5.3 Flash: Open weights. Open weights mean the checkpoint can be downloaded and self-hosted under its licence; API-only models are available solely through hosted endpoints.

Where can I run GPT-5.6 Luna and GLM 5.3 Flash?

ModelCap currently lists 3 API providers for GPT-5.6 Luna and 26 for GLM 5.3 Flash, from the OpenRouter catalogue snapshot the site serves; each model page lists the providers and their prices.

How current is this GPT-5.6 Luna vs GLM 5.3 Flash comparison?

Every figure comes from the sealed ModelCap dataset published 9 September 2026; the page re-renders within a minute of each data refresh, and the ModelCap Index positions are the same ones shown on the live rankings.

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