TL;DR
- GLM 5.3 Flash wins on: Context (4M vs 262K), speed (lower latency), cost (actually free with no caveats)
- Union Alpha wins on: Tool calling support, longer max output (131K vs 8K)
- Both are free and support text + image input
- Use GLM 5.3 Flash for: Long documents, fast iteration, production apps
- Use Union Alpha for: Agentic workflows requiring tool calling
Core Specifications
| Feature |
Union Alpha |
GLM 5.3 Flash |
| Provider |
Stealth (Anonymous) |
Zhipu AI |
| Model ID |
union-alpha |
z-ai/glm-5.3-flash |
| Price |
Free |
Free |
| Context Window |
262,144 tokens |
4,000,000 tokens |
| Max Output |
131,072 tokens |
8,192 tokens |
| Input → Output |
Text + Image → Text |
Text + Image → Text |
| Tool Calling |
✓ Supported |
✗ Not supported |
| Structured Output |
✓ (JSON mode) |
✓ (JSON mode) |
| Released |
Sep 16, 2026 |
Mar 15, 2025 |
Performance
| Metric |
Union Alpha |
GLM 5.3 Flash |
| P50 Latency |
~17.6 seconds |
~2.8 seconds |
| P50 Throughput |
~14 tokens/s |
~58 tokens/s |
| 3-day Uptime |
98.08% |
99.5%+ |
When to Choose Which
Choose Union Alpha if you need:
- Tool calling / function calling — Union Alpha is one of the few free models with this
- Long-form output — 131K max output vs GLM's 8K
- Agentic workflows — tools + reasoning + action loops
Choose GLM 5.3 Flash if you need:
- Massive context — 4M tokens = ~3 million words, perfect for entire codebases or books
- Speed — 6× lower latency, 4× higher throughput
- Production reliability — higher uptime, faster responses
- No rate limits — truly free with generous usage
API Access
Both models are available on TokenRa:
| Model |
Base URL |
Model ID |
| Union Alpha |
https://tokenra.io/v1 |
union-alpha |
| GLM 5.3 Flash |
https://tokenra.io/v1 |
z-ai/glm-5.3-flash |
View Union Alpha API docs →