Diagrams · Fig. 04

The tier ladder

Only the deterministic rung is on. Tiers 1 to 3 are built and held off by default.

The tier ladderA four-rung ladder. Tier 0, the deterministic contract diff over the ChangeKind taxonomy plus a marker scan, is live, runs first, is local and egresses nothing, and fails closed. Tier 1 cloud corpus lookup, tier 2 LLM consult and tier 3 behavioural verifier are built as in-path seams but each is held off by default and requires explicit opt-in. The default build is tier 0 only. The behavioural tier clears or refutes a change; it never proves a tool safe.TIER 3behavioural verifierexercises the changed toolclears or refutes a changeHELD OFF · OPT-INexecutes the toolTIER 2LLM consultreads the ambiguous casejudges what the diff cannotHELD OFF · OPT-INan LLM callTIER 1cloud corpus lookupone judgement, sharedjudged once, known everywhereHELD OFF · OPT-INa contract hash leavesTIER 0deterministic contract-diffChangeKind taxonomy + injection / exfil marker scandid this contract change versus what you pinned?no LLM, no scoring you cannot traceLIVE · RUNS FIRSTlocal · no egress · fail-closedTHE DEFAULT BUILD IS TIER-0 ONLY. THE BEHAVIOURAL TIER CLEARS OR REFUTES; IT NEVER PROVES A TOOL SAFE.
Fig. 04 · Only the deterministic rung is on. Tiers 1 to 3 are built and held off by default.
Read Fig. 04 as text
  TIER 3  behavioural verifier   clears or refutes a change   [ ] HELD OFF - opt-in
          exercises the changed tool                             executes the tool
  TIER 2  LLM consult            judges the ambiguous         [ ] HELD OFF - opt-in
                                                                 an LLM call
  TIER 1  cloud corpus lookup    judged once, known           [ ] HELD OFF - opt-in
                                 everywhere                      a contract hash leaves
  ---------------------------------------------------------------------------------
  TIER 0  deterministic          did this contract change     [X] LIVE - runs first
          contract-diff          versus what you pinned?          local - no egress
          ChangeKind taxonomy                                     fail-closed
          + marker scan

  the default build is tier-0 only. it egresses nothing.
  the behavioural tier clears or refutes. it never proves a tool safe.
What the figure says

A four-rung ladder. Tier 0, the deterministic contract diff over the ChangeKind taxonomy plus a marker scan, is live, runs first, is local and egresses nothing, and fails closed. Tier 1 cloud corpus lookup, tier 2 LLM consult and tier 3 behavioural verifier are built as in-path seams but each is held off by default and requires explicit opt-in. The default build is tier 0 only. The behavioural tier clears or refutes a change; it never proves a tool safe.

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Last reviewed 2026-07-27 · derived live from well-known:drift_gate.tiers · never hand-typed

Questions this answers

mcp trust tiers &middot; mcpindex tier 0 &middot; deterministic contract diff &middot; mcp gate architecture