ZMIME
Comparison · 2 models · Updated Oct 4, 2026

GPT-6 Luna vs GLM-5.3-Flash

GPT-6 Luna comes out ahead, 84 to 79 on our weighted score, and it is the cheaper option too.

  1. Our pick

    OpenAI

    GPT-6 Luna

    Released Sep 22, 2026

    84/100
    • ECI—
    • Price$0.10 / $0.50
    • Context1.05M
    Full specs Remove GPT-6 Luna

  2. Z.ai (Zhipu)

    GLM-5.3-Flash

    Released Aug 26, 2026

    79/100
    • ECI151.9
    • Price$0.15 / $0.50
    • Context1M
    Full specs Remove GLM-5.3-Flash

  3. Add a model

    Make it a three-way comparison.

01 — Verdict

GPT-6 Luna is our pick

GPT-6 Luna is the better all-round choice, scoring 84/100 against GLM-5.3-Flash (79). It leads on capability and price. GLM-5.3-Flash wins on inputs & features. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%. Capability uses the average of shared benchmarks (GPQA Diamond, FrontierMath Tiers 1–3 and OTIS Mock AIME 2024–2025), because GPT-6 Luna has no Capabilities Index score yet.

  • CapabilityGPT-6 LunaShared benchmarks: GPT-6 Luna 89.4% · GLM-5.3-Flash 79.9%
  • Lowest priceGPT-6 LunaGPT-6 Luna $0.20 · GLM-5.3-Flash $0.237 per 1M tokens (3:1 blend)
  • Longest contextGPT-6 LunaGPT-6 Luna 1,050,000 · GLM-5.3-Flash 1,000,000 tokens
  • Widest inputsGLM-5.3-FlashGPT-6 Luna: Text, Images, PDFs · GLM-5.3-Flash: Text, Images, PDFs, Video
  • Self-hostingGLM-5.3-FlashPublishes downloadable weights
How the score is built
MeasureWeightGPT-6 LunaGLM-5.3-Flash
CapabilityShared benchmarks50%8980
Price25%8379
Inputs & features15%8090
Context window10%6160
Overall100%84/10079/100
02 — Side by side

Every spec in one table

Highlighted cells lead their row. Dashes mean the data is not published.

GPT-6 Luna vs GLM-5.3-Flash specifications side by side
SpecificationGPT-6 LunaOpenAIGLM-5.3-FlashZ.ai (Zhipu)
Capability
Capabilities Index (ECI)—151.9
ECI rank—#42 of 148
GPQA DiamondGraduate-level science questions90.5% (best)90.2%
FrontierMath Tiers 1–3Research-level mathematics79.0% (best)55.8%
OTIS Mock AIME 2024–2025Competition mathematics98.9% (best)93.9%
SimpleQA VerifiedShort factual questions41.4%—
Price per million tokens
Input$0.10 (best)$0.15
Output$0.50$0.50
Cached input$0.01 (best)$0.03
Blended (3:1)$0.20 (best)$0.237
Long-context rateOver 272K: $0.20 / $0.75Same rate
Price sourceOfficial OpenAI APIOfficial Z.AI API
Limits
Context window1,050,000 tokens (best)1,000,000 tokens
Max output128,000 tokens131,072 tokens (best)
Inputs and features
TextYesYes
ImagesYesYes
PDFsYesYes
AudioNoNo
VideoNoYes
ReasoningYeslow · medium · high · xhigh · maxYeslow · high · max
Tool callingYesYes
Structured outputYesYes
Availability
WeightsProprietaryOpen
API model IDgpt-6-lunaglm-5.3-flash
API providers2465 (best)
ReleasedSep 22, 2026Aug 26, 2026
Knowledge cutoffMay 18, 2026—
03 — Cost

What would a month cost?

Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.

  • GPT-6 Luna$2.00
  • GLM-5.3-Flash$2.50
04 — Questions

Which should you choose?

Which is better: GPT-6 Luna or GLM-5.3-Flash?

GPT-6 Luna is the better all-round choice, scoring 84/100 against GLM-5.3-Flash (79). It leads on capability and price. GLM-5.3-Flash wins on inputs & features. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%. Capability uses the average of shared benchmarks (GPQA Diamond, FrontierMath Tiers 1–3 and OTIS Mock AIME 2024–2025), because GPT-6 Luna has no Capabilities Index score yet.

Which is cheaper, GPT-6 Luna or GLM-5.3-Flash?

GPT-6 Luna is cheaper at $0.10 input / $0.50 output per million tokens (official OpenAI API price). GLM-5.3-Flash costs $0.15 input / $0.50 output per million tokens (official Z.AI API price). At a typical mix of three input tokens to one output token, that is $0.20 per million tokens for GPT-6 Luna versus $0.237 for GLM-5.3-Flash (1.2× as much).

Which scores higher on benchmarks?

Not every model here has a Capabilities Index score, so we compare the average of shared benchmarks (GPQA Diamond, FrontierMath Tiers 1–3 and OTIS Mock AIME 2024–2025): GPT-6 Luna 89.4% and GLM-5.3-Flash 79.9%. On individual benchmarks: GPQA Diamond — GPT-6 Luna 90.5%, GLM-5.3-Flash 90.2%; FrontierMath Tiers 1–3 — GPT-6 Luna 79.0%, GLM-5.3-Flash 55.8%; OTIS Mock AIME 2024–2025 — GPT-6 Luna 98.9%, GLM-5.3-Flash 93.9%.

Which is better for coding?

There are no published SWE-bench Verified results for GPT-6 Luna and GLM-5.3-Flash yet, so there is no like-for-like coding score. On overall capability, GPT-6 Luna leads, which tends to carry over to coding, but test on your own codebase. Both support tool calling for agent workflows.

Which has the bigger context window?

GPT-6 Luna has the largest context window at 1,050,000 tokens, against 1,000,000 for GLM-5.3-Flash. Maximum output per response: GPT-6 Luna up to 128,000, GLM-5.3-Flash up to 131,072 tokens.

Which can read images, PDFs, audio or video?

GPT-6 Luna accepts text, images and PDFs; GLM-5.3-Flash accepts text, images, PDFs and video. GLM-5.3-Flash handles the widest range of inputs.

Are any of these open source?

GLM-5.3-Flash publishes its weights and can be self-hosted; GPT-6 Luna is proprietary.

Which is newer?

GPT-6 Luna is the newest, released Sep 22, 2026. GLM-5.3-Flash came out Aug 26, 2026. Knowledge cutoff: GPT-6 Luna May 18, 2026.

How do you decide the winner?

Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.

05 — Keep comparing

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