ReAct

The canonical observe / think / act loop, and the default architecture. Yao et al. 2022. ReAct: Synergizing Reasoning and Acting in Language Models.

                 ┌────────── loop until no tool calls ──────────┐
                 │                                              │
   prompt ───► Model ───► tool calls? ──yes──► run tools ──► results
                 │                              (parallel)
                 └─────────► no calls ───► final output

What each turn does

1. Check budget (token / cost / wall-clock); emit BUDGET_WARNING or BUDGET_EXCEEDED if needed.
2. Call the model with the current message stack + available tools.
3. Stream tokens and aggregate text + tool_calls + usage.
4. If the assistant has no tool calls, append the final message and break.
5. Otherwise dispatch every tool call in parallel under a single anyio.create_task_group. Through before_tool hooks, then permissions, then the tool host. Append the results as role=tool messages.
6. Loop back to step 1.

Usage

from loomflow import Agent
 
# Default — no kwarg needed
agent = Agent("You are helpful.", model="claude-opus-4-7")
 
# Or pass the spec explicitly
agent = Agent("...", model="...", architecture="react")
 
# Or an instance for tuning
from loomflow import ReAct
 
agent = Agent(
    "...",
    model="claude-opus-4-7",
    architecture=ReAct(),
)

max_turns lives on the Agent, not on ReAct. Pass Agent(..., max_turns=20) (default 50). Hitting the cap returns a RunResult with interrupted=True and interruption_reason="max_turns".

Parallel tool dispatch

Tool calls in the same model turn run concurrently. The model emits multiple tool_calls in one assistant message; the framework fans them out under one task group, awaits them all, then continues. Tool results are appended in arrival order. Deterministic for the model’s next turn.

A failing tool doesn’t poison the others: each tool’s exception is captured in its own ToolResult(ok=False) and the loop continues with the partial set.

When ReAct is the right call

• The number of steps is hard to predict upfront → ReAct’s one-step-at-a-time observation pays off.
• Tools occasionally fail or return surprising data that should re-shape the plan.
• You want the simplest possible loop with good production behaviour.

When to swap it out

• Cost matters and you know the steps. Plan-and-Execute or ReWOO cut LLM calls by half.
• Quality matters more than cost. ActorCritic or Reflexion iterate on output until a critic signs off.
• The problem is combinatorial. Tree of Thoughts branches and beam-searches.
• You need multiple specialists. Router / Supervisor / Swarm.