---
url: >-
  https://adk.nht.io/api/@nhtio/adk/batteries/context/thrift/subtractive_pass/variables/DEFAULT_RESERVE_FRACTION.md
description: >-
  Fallback output reserve, as a fraction of the window, used ONLY when the exact
  max-output budget is unknown.
---

# Variable: DEFAULT\_RESERVE\_FRACTION

```ts
const DEFAULT_RESERVE_FRACTION: 0.35 = 0.35;
```

Defined in: [src/batteries/context/thrift/subtractive\_pass.ts:87](https://github.com/NHTIO/ADK/blob/v1.20260713.1/src/src/batteries/context/thrift/subtractive_pass.ts#L87)

Fallback output reserve, as a fraction of the window, used ONLY when the exact max-output budget is
unknown.

## Remarks

Prefer passing the caller's actual generation `maxTokens` as `outputReserve` — reserving a flat
fraction of the window when the model can emit at most, say, 2048 tokens throws away real input
budget (RAG chunks, history) for output that can never be produced. This fraction is the calibrated
value from the flagship reference agent (0.35 of the window), kept as the default for a caller who
genuinely doesn't know their generation cap yet.