API cost decision in 10 seconds

🔥GLM 5.3 Flash vs NewGPT-6 Luna

Pick GPT-6 Luna for lower cost; pick GLM 5.3 Flash only if the larger context window matters more.

Page updated: 2026-09-22T19:07:54Z Data confirmed: 2026-09-22T20:07:50Z Prices normalized to USD per 1M tokens Sample workload: 1M input + 500K output

Budget verdict

Pick GPT-6 Luna for lower cost; pick GLM 5.3 Flash only if the larger context window matters more.

On the standard 1M input plus 500K output workload, GPT-6 Luna is estimated at $0.35 vs $0.4 for GLM 5.3 Flash, saving $0.05 (12.5% lower).

Cost-first pickGPT-6 Luna

Context-first pickGLM 5.3 Flash

Sample savings$0.0512.5%

10x traffic gap$0.5

GLM 5.3 Flash has more context, but GPT-6 Luna saves $0.05 on the standard workload. At 10x that traffic, the same price gap is about $0.5. Use the calculator below to replace the sample workload with your own token volume.

Cost sensitivity

Workload Sensitivity

Same prices, different token mixes.

GPT-6 Luna stays cheaper across input-heavy, balanced, and output-heavy sample workloads.

Workload shape	Token mix	Better pick	GLM 5.3 Flash	GPT-6 Luna
Input-heavy / RAG	5M input + 500K output	GPT-6 Luna	$1	$0.75
Balanced workload	1M input + 1M output	GPT-6 Luna	$0.65	$0.6
Output-heavy chatbot	1M input + 5M output	GPT-6 Luna	$2.65	$2.6

Cheaper input GPT-6 Luna $0.15 vs $0.1 / 1M

GPT-6 Luna is $0.05 cheaper per 1M input tokens (33.3% lower; 1.5x difference).

Cheaper output Tie $0.5 vs $0.5 / 1M

Both models report the same output price at $0.5 per 1M tokens.

Larger context GLM 5.3 Flash 1.31M vs 1.05M

GLM 5.3 Flash has 260.72K more context (1.25x larger).

Sample workload GPT-6 Luna $0.4 vs $0.35

GPT-6 Luna is $0.05 cheaper on the standard workload (12.5% lower).

Estimate your workload cost

Your Workload Cost

Prices are normalized to USD per 1M tokens.

Monthly input tokens Monthly output tokens

GLM 5.3 Flash Calculating… Estimated API cost

GPT-6 Luna Calculating… Estimated API cost

Cheaper for this workload Calculating… Difference: calculating…

This estimate uses normalized public API pricing per 1M tokens. It is a planning aid, not a billing quote. Verify provider pricing, limits, and terms before production use.

Quick Decision

Verdict

GPT-6 Luna has the lower input price; both models tie on output price; GLM 5.3 Flash offers the larger context window. For the 1M input plus 500K output sample, GPT-6 Luna is cheaper for the standard workload.

For a 1M input token plus 500K output token workload, the estimated API cost is $0.4 for GLM 5.3 Flash and $0.35 for GPT-6 Luna.

Best Fit

Choose GLM 5.3 Flash when you care most about larger context window.

Choose GPT-6 Luna when you care most about lower input-token price.

Decision Notes

On the standard 1M input plus 500K output workload, GPT-6 Luna is estimated at $0.35 vs $0.4 for GLM 5.3 Flash, saving $0.05 (12.5% lower).
GPT-6 Luna is $0.05 cheaper on the standard workload (12.5% lower).
GPT-6 Luna is $0.05 cheaper per 1M input tokens (33.3% lower; 1.5x difference).
Both models report the same output price at $0.5 per 1M tokens.
GLM 5.3 Flash has 260.72K more context (1.25x larger).

Head-to-Head Specs

Feature	🔥GLM 5.3 Flash (Z.ai)	NewGPT-6 Luna (OpenAI)
Input Price prompt tokens per 1M	$0.15	$0.1
Completion Price per 1M tokens	$0.5	$0.5
Sample Workload Cost 1M input + 500K output	$0.4	$0.35
Context Window	1.31M	1.05M
Release Date	2026-08-26	2026-09-22
Popularity	#4

Use-Case Decision Matrix

Use case	Better pick	Why
Budget-constrained production	GPT-6 Luna	On the standard 1M input plus 500K output workload, GPT-6 Luna is estimated at $0.35 vs $0.4 for GLM 5.3 Flash, saving $0.05 (12.5% lower).
High-volume input processing	GPT-6 Luna	Lower prompt-token price matters most when prompts, retrieved passages, or documents dominate the bill.
Long responses and chatbots	Tie	Lower output-token price matters most when assistants generate many completion tokens.
RAG or long-document work	GLM 5.3 Flash	A larger context window leaves more room for retrieved passages, conversation history, or source files.

Related Alternatives

Same-provider lower-cost swaps

GLM 5.2 (free) can replace GLM 5.3 Flash when lower sample workload cost matters most: $0.
GLM 4.5 Air (free) can replace GLM 5.3 Flash when lower sample workload cost matters most: $0.
GLM 4 32B can replace GLM 5.3 Flash when lower sample workload cost matters most: $0.15.
GLM 5.3 Flash (batch) can replace GLM 5.3 Flash when lower sample workload cost matters most: $0.16.

Larger context near this budget

No larger-context model is currently tracked within a close sample-cost band.

Popular competitors

MiMo-V2.6-Pro · Xiaomi · #1
Qwen3.8 Max (0902) · Qwen · #2
DeepSeek V4.1 Flash · DeepSeek · #3
Hy4 preview · Tencent · #5

Cheaper alternatives

Review low-cost models sorted by a standard 1M input plus 500K output workload.

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Larger context alternatives

Find models with larger context windows for RAG, long documents, and codebase review.

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Provider catalogs

Compare models within provider hubs before choosing a final API vendor.

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Z.ai catalog

Review all tracked Z.ai models before deciding whether this matchup is the right shortlist.

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OpenAI catalog

Check other OpenAI models with comparable pricing, context, or release timing.

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GLM 5.3 Flash

GLM-5.3-Flash is a native multimodal model from Z.ai. It is suited for efficient coding and long-horizon agent tasks. Its hybrid sparse and linear attention architecture maintains accurate long-context behavior while...

GPT-6 Luna

GPT-6 Luna is the fast, cost-efficient model in OpenAI's GPT-6 series, positioned below GPT-6 Sol. It is suited for high-volume and latency-sensitive workloads such as chat, classification, and lightweight agentic...