---
title: "Gemini API — Preview Models Have Stricter Rate Limits Than Stable"
aliases: [gemini-preview-rate-limits, gemini-rpm-limits, gemini-429-preview]
tags: [gemini, google-ai, rate-limits, multi-agent, baic, debugging]
sources:
  - "daily/2026-05-18.md"
created: 2026-05-18
updated: 2026-05-18
---

# Gemini API — Preview Models Have Stricter Rate Limits Than Stable

Models with `-preview` in their name (e.g., `gemini-3.1-pro-preview`, `gemini-3.1-flash-preview`) have **5–10× stricter RPM limits** than their stable counterparts. This limit is not prominently documented and causes 429 / 504 errors that look like transient network issues.

## The Pattern

```python
# WRONG — preview model hits rate limits fast in multi-agent setups
model = "gemini-3.1-pro-preview"

# CORRECT — stable model has much higher RPM ceiling
model = "gemini-3.1-flash-lite"          # or "gemini-3.1-pro" (stable)
```

## Why It Happens

- Google uses preview models to test new capabilities under controlled load
- Rate limits on preview models are intentionally low to prevent over-reliance before GA
- In a multi-agent system, N parallel agents each make independent API calls — RPM exposure multiplies by N
- The result is a burst of 429s which the API gateway surfaces as 504 after timeout

## Diagnostic Signals

1. `429 Too Many Requests` — immediate rate limit hit
2. `504 Gateway Timeout` — rate limit reached, upstream gave up waiting
3. Errors appear only under parallel load (single-agent tests pass fine)
4. Errors correlate with `-preview` model IDs in logs

## Fix

Replace `-preview` model IDs with stable equivalents:

| Preview (avoid in prod) | Stable replacement |
|------------------------|-------------------|
| `gemini-3.1-pro-preview` | `gemini-3.1-pro` |
| `gemini-3.1-flash-preview` | `gemini-3.1-flash-lite` |
| `gemini-2.5-pro-preview-*` | `gemini-2.5-pro` (when GA) |

## Multi-Agent Amplification

In a multi-agent system with N concurrent agents:
- Each agent independently counts toward the shared RPM quota
- A 10 RPM preview limit with 5 parallel agents = effectively 2 RPM per agent
- Use stable models in production; preview models only in single-agent dev/test

## Related Concepts

- [[wiki/concepts/gemini-conversation-cost-scaling]] — token cost per conversation turn in Gemini
- [[wiki/llm-models/_index]] — full Gemini model catalog with stable IDs

## Sources

- [[daily/2026-05-18.md]] — Discovered during BAIC multi-agent system debugging; 504/429 errors caused by parallel agents all using `gemini-3.1-pro-preview`; fixed by switching to `gemini-3.1-flash-lite`
