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Documentation Index

Fetch the complete documentation index at: https://reasonblocks.mintlify.app/llms.txt

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FSMState is the enum at the heart of ReasonBlocks’ difficulty tracking. After scoring each reasoning step, the SDK advances a finite state machine through these states to determine whether to skip E-trace retrieval, switch models, or escalate to a more aggressive intervention. You read the current state from TraceState.current_state and from individual StepRecord.state fields in step_log. 
from reasonblocks.types import FSMState

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States

StateTrigger conditionBehavior
INITStart of every runTransitions to NORMAL on the first scored step
FASTAll recent steps below fast_threshold (0.2)Skips E-trace retrieval; routes to cheap model if routing is configured
NORMALDefault when difficulty is neither consistently low nor highFull E-trace pipeline runs; default model used
SLOWAll recent steps above slow_threshold (0.6)Routes to strong model if routing is configured; E-trace injection enabled
SKIPExtended struggle: 35+ consecutive steps above skip_threshold (0.85)Most severe intervention; the SDK forces a skip injection to break the loop
ENDAgent produced a final answerRun is complete; no further scoring or injection occurs

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State reference

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FSMState.INIT

The machine starts in INIT at the beginning of every run. It does not persist past the first scored step — the FSM transitions to NORMAL immediately after the first step is assessed. You will typically only see INIT in StepRecord.state for step index 0.

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FSMState.FAST

The FSM enters FAST when all steps in the recent difficulty window fall below fast_threshold (default 0.2). In FAST state, the SDK skips the E-trace retrieval round-trip entirely — the agent is performing well and does not need steering. If you have model routing configured, the SDK routes the next LLM call to the cheaper fast model.

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FSMState.NORMAL

NORMAL is the default operating state. The full E-trace pipeline runs: the SDK queries the pattern store, ranks results by similarity, and injects the best-matching guidance into the system prompt. The model specified in your ReasonBlocks config is used without rerouting.

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FSMState.SLOW

The FSM transitions to SLOW when all steps in the recent window exceed slow_threshold (default 0.6). This indicates the agent is consistently struggling. E-trace injection continues, and if model routing is configured the SDK upgrades the next call to the strong model.
The FSM uses hysteresis — it requires the entire recent window to be above or below the threshold before changing state. A single high-difficulty step does not immediately push the run into SLOW.

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FSMState.SKIP

SKIP is the most severe intervention state. The FSM enters SKIP after 35 or more consecutive steps where difficulty exceeds skip_threshold (default 0.85). At this point the SDK injects a hard skip directive into the system prompt, instructing the agent to exit its current approach and produce a partial answer. This is a last-resort measure to prevent infinite loops from consuming your entire token budget.
Once the FSM enters SKIP, every subsequent step receives the skip injection until the agent produces a final answer and transitions to END. You cannot manually reset the state mid-run.

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FSMState.END

The FSM enters END when the agent emits a final answer. No further step scoring, E-trace retrieval, or injection occurs after this transition. The TraceState is frozen and available for inspection.

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Checking the current state

After a run completes, read current_state from the middleware’s step_log: 
from reasonblocks import ReasonBlocks
from reasonblocks.types import FSMState

rb = ReasonBlocks(api_key="rb_live_...")

with rb.middleware(run_id="run-1", agent_name="bugfixer", task="...") as mw:
    result = agent.invoke({"messages": [("user", "Fix the failing tests.")]})

# mw.step_log is a list[StepLogEntry], one entry per model call
for entry in mw.step_log:
    print(entry.step, entry.fsm_state, entry.difficulty)

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Values

FSMState is a standard Python enum.Enum. Each member’s .value is its uppercase string name, which is also what appears in the ReasonBlocks dashboard and API responses. 
FSMState.FAST.value    # "FAST"
FSMState.NORMAL.value  # "NORMAL"
FSMState.SLOW.value    # "SLOW"
FSMState.SKIP.value    # "SKIP"
FSMState.INIT.value    # "INIT"
FSMState.END.value     # "END"