Cheaper overall
GPT-6 Luna
16% lower blended rate
Cheaper on long prompts
GLM 5.3 Flash
above 272,000 input tokens
Bigger context window
GPT-6 Luna
1,050,000 vs 1,000,000 tokens
Cheaper cached input
GPT-6 Luna
$0.01 vs $0.03, 67% less
Where each one wins
GPT-6 Luna
- Cheaper input tokens $0.10 vs $0.15, 33% less
- Cheaper cached input $0.01 vs $0.03, 67% less
- Larger context window 1,050,000 tokens
- Higher long-context reasoning (AA-LCR) 83.3 vs 80
- Higher scientific coding (SciCode) 54.6 vs 51.6
- Higher physics research reasoning (CritPt) 19.4 vs 15.4
- Ahead on 1 more benchmark figure
- Offers Batch, Flex and Priority pricing not listed for GLM 5.3 Flash
GLM 5.3 Flash
- Cheaper on long prompts above 272,000 input tokens
- Higher overall intelligence (Intelligence Index) 41.9 vs 37.3
- Higher expert-exam performance (Humanity's Last Exam) 39.9 vs 38.5
- Higher real-world task performance (GDPval) 57.7 vs 43.4
- Ahead on 1 more benchmark figure
What four workloads cost
One run, and the same run a thousand times.
The gap opens on long prompts: GLM 5.3 Flash costs $0.0615 against $0.0823, a difference of $20.75 over a thousand runs.
| Workload | GPT-6 Luna | GLM 5.3 Flash | ×1,000 | Difference |
|---|---|---|---|---|
| Chat turn 1,000 in / 500 out | $0.0004 | $0.0004 | $0.3500 / $0.4000 | GPT-6 Luna is 13% cheaper |
| RAG answer 10,000 in / 800 out | $0.0014 | $0.0019 | $1.40 / $1.90 | GPT-6 Luna is 26% cheaper |
| Agent loop 32,000 in / 700 out × 20 calls | $0.0170 | $0.0310 | $17.00 / $31.00 | GPT-6 Luna is 45% cheaper |
| Long document 400,000 in / 3,000 out | $0.0823 | $0.0615 | $82.25 / $61.50 | GLM 5.3 Flash is 25% cheaper |
Price per 1M tokens
Above 272,000 input tokens the rates change, and the new rate applies to the whole request, not just the tokens past that point: GPT-6 Luna's input goes from $0.1000 to $0.2000. That is where the cheaper model changes.
| Context band | Price | GPT-6 Luna | GLM 5.3 Flash | Difference |
|---|---|---|---|---|
| Prompts up to 272,000 tokens | Input | $0.10 | $0.15 | GPT-6 Luna is 33% cheaper |
| Prompts up to 272,000 tokens | Cached input | $0.01 | $0.03 | GPT-6 Luna is 67% cheaper |
| Prompts up to 272,000 tokens | Output | $0.50 | $0.50 | Same |
| Prompts over 272,000 tokens | Input | $0.20 | $0.15 | GLM 5.3 Flash is 25% cheaper |
| Prompts over 272,000 tokens | Cached input | $0.02 | $0.03 | GPT-6 Luna is 33% cheaper |
| Prompts over 272,000 tokens | Output | $0.75 | $0.50 | GLM 5.3 Flash is 33% cheaper |
Blended: GPT-6 Luna $0.20, GLM 5.3 Flash $0.2375 per 1M — one rate at 3:1 input to output, for comparing two models at a glance.
GPT-6 Luna priced by OpenAI, GLM 5.3 Flash by Z.ai. Standard tier, pay-as-you-go.
Other pricing tiers
Only GPT-6 Luna lists Batch, Flex and Priority, at up to 50% off its own standard rate; GLM 5.3 Flash offers none of them.
Every tier either model sells is here, so this is the whole price sheet. A saving is measured against that model's own standard rate — how we read tiers.
| Tier | GPT-6 Luna | GLM 5.3 Flash | Cheaper |
|---|---|---|---|
| Batch only on GPT-6 Luna | $0.05 in / $0.25 out 50% off Standard | Not offered | — |
| Flex only on GPT-6 Luna | $0.05 in / $0.25 out 50% off Standard | Not offered | — |
| Priority only on GPT-6 Luna | $0.20 in / $1.00 out | Not offered | — |
Benchmarks
They share 8 figures: GPT-6 Luna leads on 4, GLM 5.3 Flash on 4. The widest gap is 49.1 points, on answer reliability (Omniscience Non-Hallucination).
Overall intelligence
Intelligence Index — Overall intelligence across reasoning, knowledge & math evals
GLM 5.3 Flash ahead by 4.6
Expert-exam performance
Humanity's Last Exam — Expert-level questions across many academic domains
GLM 5.3 Flash ahead by 1.4
Long-context reasoning
AA-LCR — Long-context reasoning across large inputs
GPT-6 Luna ahead by 3.3
Scientific coding
SciCode — Research-level scientific coding tasks
GPT-6 Luna ahead by 3
Physics research reasoning
CritPt — Unpublished physics research reasoning problems
GPT-6 Luna ahead by 4
Real-world task performance
GDPval — Economically valuable, real-world knowledge work
GLM 5.3 Flash ahead by 14.3
Factual accuracy
Omniscience Accuracy — Breadth of factual knowledge across domains
GPT-6 Luna ahead by 16.3
Answer reliability
Omniscience Non-Hallucination — How reliably the model avoids fabricated answers
GLM 5.3 Flash ahead by 49.1
Each figure is that model's best published run, with the effort level named beside it — where these scores come from.
Specifications
GPT-6 Luna holds 50,000 more input tokens in one request. GLM 5.3 Flash also takes video. Only GPT-6 Luna lists web search; only GLM 5.3 Flash lists open weights.
| Specification | GPT-6 Luna | GLM 5.3 Flash |
|---|---|---|
| Context window | 1,050,000 tokens | 1,000,000 tokens |
| Max output | 128,000 tokens | 128,000 tokens |
| Takes in | Text, image, file | Text, image, video, file |
| Puts out | Text | Text |
| Knowledge cutoff | 18 May 2026 | — |
| Released | 22 Sep 2026 | 26 Aug 2026 |
| Status | Active | Active |
| Sold by | OpenAI | Perplexity, Z.ai |
| Tool use | Yes | Yes |
| Structured outputs | Yes | Yes |
| Web search | Yes | Not listed |
| Prompt caching | Yes | Yes |
| Code execution | Yes | Yes |
| Computer use | Yes | Yes |
| Open weights | Not listed | Yes |
| Reasoning | Yes | Yes |
FAQs
- Is GPT-6 Luna cheaper than GLM 5.3 Flash?
- Yes. A 1,000-token prompt with a 500-token reply costs $0.0004 on GPT-6 Luna and $0.0004 on GLM 5.3 Flash.
- How much do GPT-6 Luna and GLM 5.3 Flash cost per 1M tokens?
- GPT-6 Luna costs $0.10 for input and $0.50 for output. GLM 5.3 Flash costs $0.15 and $0.50. Standard pay-as-you-go rates, as of 22 Sep 2026.
- Which is better, GPT-6 Luna or GLM 5.3 Flash?
- On published benchmarks, GLM 5.3 Flash. It leads on 4 of the 8 figures both models report, including overall intelligence (Intelligence Index), where it scores 41.9 against 37.3.
- Is GPT-6 Luna or GLM 5.3 Flash cheaper for long prompts?
- GLM 5.3 Flash, above 272,000 input tokens. A rate that changes at a context length applies to the whole request, not only the tokens past it, so the switch is sharp rather than gradual.
- Does GPT-6 Luna or GLM 5.3 Flash offer batch pricing?
- GPT-6 Luna only. Its batch input costs $0.05, 50% off its standard rate, and GLM 5.3 Flash lists no batch tier at all.
- Does GPT-6 Luna or GLM 5.3 Flash have a bigger context window?
- GPT-6 Luna, at 1,050,000 tokens against 1,000,000. That is 50,000 more input tokens in a single request.