GLM 5.3 Flash vs GPT OSS 20 B: cost comparison
Prices updated 2026-11-01 · computed from live provider data
Short answer: GPT OSS 20 B is cheaper on a
3:1 input/output blend — $0.028 per million tokens versus
$0.050, a 43% difference.
GLM 5.3 Flash offers the larger context window at 1,048,576 tokens, against 131,072 for GPT OSS 20 B.
Head to head
| GLM 5.3 Flash | GPT OSS 20 B | |
|---|---|---|
| Input, per 1M tokens | $0.013 | $0.015 |
| Output, per 1M tokens | $0.158 | $0.070 |
| Blended 3:1, per 1M | $0.050 | $0.028 |
| Context window | 1,048,576 | 131,072 |
| Vendor | z-ai | darkbloom |
Monthly cost at real volumes
| Workload (input / output) | GLM 5.3 Flash | GPT OSS 20 B |
|---|---|---|
| 1M in / 250K out | $0.053 | $0.032 |
| 10M in / 2.5M out | $0.529 | $0.320 |
| 100M in / 25M out | $5.29 | $3.20 |
Which should you pick?
Pick GLM 5.3 Flash when you need the longer context window (1,048,576 vs 131,072 tokens). Pick GPT OSS 20 B when price per token dominates your workload — high-volume classification, extraction, or batch summarisation.