# Speculative execution (agents)

**Source:** https://promtable.com/glossary/speculative-execution

> Speculative execution in agents launches multiple plausible tool calls in parallel before knowing which the user wants — accepting the winning result and discarding the others — to cut perceived latency.

---
Speculative execution in agents launches multiple plausible tool calls in parallel before knowing which the user wants — accepting the winning result and discarding the others — to cut perceived latency.

Distinct from speculative decoding (token-level), speculative execution operates at the agent step level. The agent predicts the most likely tool call and pre-runs it in parallel with the LLM's actual decision; if the prediction matches, the result is already ready; if not, the unused result is discarded. Used heavily in voice agents and latency-critical assistants in 2026 where waiting on tool calls before responding produces awkward pauses. The cost is wasted compute on rejected predictions; the win is materially better perceived latency on the happy path.

## When to use

- Latency-critical voice agents.
- Realtime assistants where tool calls add noticeable lag.

## Common mistakes

- Speculating too widely — wastes compute without consistent wins.
- Side-effecting speculative calls — tools that change state can't be rolled back.

## Related terms

- [agent](https://promtable.com/glossary/agent)
- [agent-loop](https://promtable.com/glossary/agent-loop)
- [voice](https://promtable.com/glossary/voice)
- [speculative-decoding](https://promtable.com/glossary/speculative-decoding)

*Last updated: 2026-06-01*
---

Original page: https://promtable.com/glossary/speculative-execution
Maintained by Promtable (https://promtable.com). Content: CC BY 4.0. Cite as "Promtable — https://promtable.com/glossary/speculative-execution".
Contact: info@vibecodingturkey.com.