{
 "measurement": "Re-verification of the MCP per-tool curves on Claude Code 2.1.246",
 "claude_code_version": "2.1.246",
 "claude_code_version_recorded_at_runtime": "2.1.246 (Claude Code)",
 "trial_date": "2026-08-27",
 "supersedes": "mcp-curve-2-1-238.json for the curve figures only. That corpus also carried an isolation control; this one could not reproduce that control and says so below rather than omitting it.",
 "headline": "Every cell is byte-identical to the previous release and every cell is single-valued across four rounds with zero spread. The isolation control could NOT be run: its unisolated arm lost two of four rounds and its baseline moved 5,271 tokens between the two that survived.",
 "method": {
  "fixture": "A minimal stdio MCP server advertising a controllable number of tools, each with a fixed 798-byte definition, read back out of the server's own tools/list reply so the tool count is a measured fact rather than an argument that was passed.",
  "pairing": "Each arm is paired against a floor measured with ITS OWN tool-search flag state. Pairing the loaded arm against a tool-search-ON floor would fold the switch cost into the per-tool figure and bill it twice beside BASELINE.on/off.",
  "isolation": "--setting-sources project asserted onto the command line for every call.",
  "estimator": "Every cell is single-valued, so the per-round list IS the result. No median is published: it would imply a smoothing that did not happen.",
  "population": "Four rounds per cell, all usable, pooled.",
  "controls": {
   "arrival": "The reply had to be exactly OK.",
   "flag_both_ways": "ENABLE_TOOL_SEARCH asserted present on the loaded arm and ABSENT on the deferred arm, so the treatment is proved on both sides.",
   "usable": "result_guard was added to this harness before the run and rejects a result whose modelUsage is empty or which reports an error. Control-tested against a synthetic 529 first.",
   "fixture_read_back": "Every run recorded 798 bytes per definition."
  }
 },
 "results": {
  "curve": {
   "mcp_deferred": {
    "5": {
     "delta": 90,
     "all_rounds": [
      90,
      90,
      90,
      90
     ],
     "rounds": 4,
     "min": 90,
     "max": 90,
     "spread": 0,
     "per_tool": 18.0,
     "previous_release_delta": 90.0,
     "unchanged_since_previous": true
    },
    "50": {
     "delta": 810,
     "all_rounds": [
      810,
      810,
      810,
      810
     ],
     "rounds": 4,
     "min": 810,
     "max": 810,
     "spread": 0,
     "per_tool": 16.2,
     "previous_release_delta": 810.0,
     "unchanged_since_previous": true
    },
    "200": {
     "delta": 3210,
     "all_rounds": [
      3210,
      3210,
      3210,
      3210
     ],
     "rounds": 4,
     "min": 3210,
     "max": 3210,
     "spread": 0,
     "per_tool": 16.05,
     "previous_release_delta": 3210.0,
     "unchanged_since_previous": true
    }
   },
   "mcp_loaded": {
    "5": {
     "delta": 3270,
     "all_rounds": [
      3270,
      3270,
      3270,
      3270
     ],
     "rounds": 4,
     "min": 3270,
     "max": 3270,
     "spread": 0,
     "per_tool": 654.0,
     "previous_release_delta": 3270.0,
     "unchanged_since_previous": true
    },
    "50": {
     "delta": 32610,
     "all_rounds": [
      32610,
      32610,
      32610,
      32610
     ],
     "rounds": 4,
     "min": 32610,
     "max": 32610,
     "spread": 0,
     "per_tool": 652.2,
     "previous_release_delta": 32610.0,
     "unchanged_since_previous": true
    },
    "200": {
     "delta": 130410,
     "all_rounds": [
      130410,
      130410,
      130410,
      130410
     ],
     "rounds": 4,
     "min": 130410,
     "max": 130410,
     "spread": 0,
     "per_tool": 652.05,
     "previous_release_delta": 130410.0,
     "unchanged_since_previous": true
    }
   }
  },
  "calculator_curves_now": {
   "mcpDeferred": [
    [
     0,
     0
    ],
    [
     5,
     90
    ],
    [
     50,
     810
    ],
    [
     200,
     3210
    ]
   ],
   "mcpLoaded": [
    [
     0,
     0
    ],
    [
     5,
     3270
    ],
    [
     50,
     32610
    ],
    [
     200,
     130410
    ]
   ]
  },
  "every_cell_unchanged_since_previous_release": true,
  "every_cell_single_valued": true,
  "floors_this_run": {
   "tool_search_on": [
    22793
   ],
   "tool_search_off": [
    37862
   ]
  },
  "isolation_control_ATTEMPTED_AND_FAILED": {
   "why_it_is_reported_not_omitted": "The previous corpus published this control, so dropping it silently would look like it had passed.",
   "rounds_attempted": 4,
   "rounds_usable": 2,
   "unisolated_floor_readings": [
    94509,
    99780
   ],
   "unisolated_floor_spread": 5271,
   "isolated_floor_readings": [
    37874
   ],
   "what_went_wrong": "The unisolated arm loads this machine's user-scope configuration. Two of four rounds lost that floor entirely, and the two that survived disagreed by thousands of tokens, so every delta computed against it inherits that movement. On the previous release the unisolated deltas matched the isolated ones, which is what made the control meaningful.",
   "no_cause_claimed": "What moved the unisolated baseline between rounds is NOT established. It is this machine's own configuration and nothing here isolates which part of it changed or why, so no direction or mechanism is asserted.",
   "consequence": "The per-tool figures below rest on the ISOLATED arm alone, which is what the calculator uses. The claim the control would have supported, that the per-tool cost is the same whether or not user config is loaded, is NOT re-established on this release and should not be read as carried forward."
  }
 },
 "known_limits": {
  "one_tool_shape": "CARRIED FORWARD from the previous corpus. Every definition is 798 bytes built from repeated characters, which is the published fixture and is what makes the cross-version comparison valid, but a run of one character tokenises far worse than prose. A real 798-byte schema will not cost the same. The comparison across versions is sound; the absolute per-tool figure is fixture-specific.",
  "no_explanation_for_the_doubling": "CARRIED FORWARD. A loaded tool measured 304 tokens on 2.1.223/224 and 652 here. Nothing identifies what changed or in which release.",
  "the_deferred_arm_noise_is_RETIRED": "The previous corpus limited itself because the tool-search-ON floor carried an intermittent component that gave every deferred cell a 719-token spread, as large as the measurement at 5 and 50 tools. On this release every deferred cell returned the SAME value in all four rounds, spread zero. RETIRED, and the histograms above are the evidence.",
  "the_isolation_control_is_not_carried_forward": "See the failed-control block. Its claim is not re-established on this release.",
  "one_machine_one_model": "Opus on Claude Code 2.1.246, one machine."
 },
 "runs": {
  "curve": [
   {
    "arm": "floor_tool_search_on",
    "n": 0,
    "round": 0,
    "status": "ok",
    "tool_search_off": false,
    "context": 22793,
    "delta": 0
   },
   {
    "arm": "floor_tool_search_off",
    "n": 0,
    "round": 0,
    "status": "ok",
    "tool_search_off": true,
    "context": 37862,
    "delta": 0
   },
   {
    "arm": "mcp_deferred",
    "n": 5,
    "round": 0,
    "status": "ok",
    "tool_search_off": false,
    "tools_served_by_server": 5,
    "bytes_per_tool_definition": 798,
    "paired_floor": 22793,
    "context": 22883,
    "delta": 90,
    "per_tool": 18.0
   },
   {
    "arm": "mcp_loaded",
    "n": 5,
    "round": 0,
    "status": "ok",
    "tool_search_off": true,
    "tools_served_by_server": 5,
    "bytes_per_tool_definition": 798,
    "paired_floor": 37862,
    "context": 41132,
    "delta": 3270,
    "per_tool": 654.0
   },
   {
    "arm": "mcp_deferred",
    "n": 50,
    "round": 0,
    "status": "ok",
    "tool_search_off": false,
    "tools_served_by_server": 50,
    "bytes_per_tool_definition": 798,
    "paired_floor": 22793,
    "context": 23603,
    "delta": 810,
    "per_tool": 16.2
   },
   {
    "arm": "mcp_loaded",
    "n": 50,
    "round": 0,
    "status": "ok",
    "tool_search_off": true,
    "tools_served_by_server": 50,
    "bytes_per_tool_definition": 798,
    "paired_floor": 37862,
    "context": 70472,
    "delta": 32610,
    "per_tool": 652.2
   },
   {
    "arm": "mcp_deferred",
    "n": 200,
    "round": 0,
    "status": "ok",
    "tool_search_off": false,
    "tools_served_by_server": 200,
    "bytes_per_tool_definition": 798,
    "paired_floor": 22793,
    "context": 26003,
    "delta": 3210,
    "per_tool": 16.05
   },
   {
    "arm": "mcp_loaded",
    "n": 200,
    "round": 0,
    "status": "ok",
    "tool_search_off": true,
    "tools_served_by_server": 200,
    "bytes_per_tool_definition": 798,
    "paired_floor": 37862,
    "context": 168272,
    "delta": 130410,
    "per_tool": 652.05
   },
   {
    "arm": "floor_tool_search_on",
    "n": 0,
    "round": 1,
    "status": "ok",
    "tool_search_off": false,
    "context": 22793,
    "delta": 0
   },
   {
    "arm": "floor_tool_search_off",
    "n": 0,
    "round": 1,
    "status": "ok",
    "tool_search_off": true,
    "context": 37862,
    "delta": 0
   },
   {
    "arm": "mcp_deferred",
    "n": 5,
    "round": 1,
    "status": "ok",
    "tool_search_off": false,
    "tools_served_by_server": 5,
    "bytes_per_tool_definition": 798,
    "paired_floor": 22793,
    "context": 22883,
    "delta": 90,
    "per_tool": 18.0
   },
   {
    "arm": "mcp_loaded",
    "n": 5,
    "round": 1,
    "status": "ok",
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    "paired_floor": 37862,
    "context": 41132,
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    "per_tool": 654.0
   },
   {
    "arm": "mcp_deferred",
    "n": 50,
    "round": 1,
    "status": "ok",
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    "bytes_per_tool_definition": 798,
    "paired_floor": 22793,
    "context": 23603,
    "delta": 810,
    "per_tool": 16.2
   },
   {
    "arm": "mcp_loaded",
    "n": 50,
    "round": 1,
    "status": "ok",
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    "bytes_per_tool_definition": 798,
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    "per_tool": 652.2
   },
   {
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   },
   {
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   },
   {
    "arm": "floor_tool_search_on",
    "n": 0,
    "round": 2,
    "status": "ok",
    "tool_search_off": false,
    "context": 22793,
    "delta": 0
   },
   {
    "arm": "floor_tool_search_off",
    "n": 0,
    "round": 2,
    "status": "ok",
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    "context": 37862,
    "delta": 0
   },
   {
    "arm": "mcp_deferred",
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    "status": "ok",
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   },
   {
    "arm": "mcp_loaded",
    "n": 5,
    "round": 2,
    "status": "ok",
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   },
   {
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    "round": 2,
    "status": "ok",
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    "bytes_per_tool_definition": 798,
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    "context": 23603,
    "delta": 810,
    "per_tool": 16.2
   },
   {
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    "round": 2,
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    "paired_floor": 37862,
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    "delta": 32610,
    "per_tool": 652.2
   },
   {
    "arm": "mcp_deferred",
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    "round": 2,
    "status": "ok",
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    "tools_served_by_server": 200,
    "bytes_per_tool_definition": 798,
    "paired_floor": 22793,
    "context": 26003,
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    "per_tool": 16.05
   },
   {
    "arm": "mcp_loaded",
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    "round": 2,
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    "bytes_per_tool_definition": 798,
    "paired_floor": 37862,
    "context": 168272,
    "delta": 130410,
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   },
   {
    "arm": "floor_tool_search_on",
    "n": 0,
    "round": 3,
    "status": "ok",
    "tool_search_off": false,
    "context": 22793,
    "delta": 0
   },
   {
    "arm": "floor_tool_search_off",
    "n": 0,
    "round": 3,
    "status": "ok",
    "tool_search_off": true,
    "context": 37862,
    "delta": 0
   },
   {
    "arm": "mcp_deferred",
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    "round": 3,
    "status": "ok",
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    "bytes_per_tool_definition": 798,
    "paired_floor": 22793,
    "context": 22883,
    "delta": 90,
    "per_tool": 18.0
   },
   {
    "arm": "mcp_loaded",
    "n": 5,
    "round": 3,
    "status": "ok",
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    "bytes_per_tool_definition": 798,
    "paired_floor": 37862,
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   },
   {
    "arm": "mcp_deferred",
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    "round": 3,
    "status": "ok",
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    "bytes_per_tool_definition": 798,
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    "per_tool": 16.2
   },
   {
    "arm": "mcp_loaded",
    "n": 50,
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    "status": "ok",
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    "bytes_per_tool_definition": 798,
    "paired_floor": 37862,
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    "delta": 32610,
    "per_tool": 652.2
   },
   {
    "arm": "mcp_deferred",
    "n": 200,
    "round": 3,
    "status": "ok",
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   },
   {
    "arm": "mcp_loaded",
    "n": 200,
    "round": 3,
    "status": "ok",
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   }
  ],
  "bridge_attempt": [
   {
    "arm": "floor_isolated",
    "n": 0,
    "round": 0,
    "status": "ok",
    "isolated": true,
    "tool_search_off": true,
    "context": 37874,
    "delta": 0
   },
   {
    "arm": "floor_unisolated",
    "n": 0,
    "round": 0,
    "status": "ok",
    "isolated": false,
    "tool_search_off": true,
    "context": 94509,
    "delta": 0
   },
   {
    "arm": "loaded_isolated",
    "n": 5,
    "round": 0,
    "status": "ok",
    "isolated": true,
    "tool_search_off": true,
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    "paired_floor": 37874,
    "context": 41140,
    "delta": 3266,
    "per_tool": 653.2
   },
   {
    "arm": "loaded_unisolated",
    "n": 5,
    "round": 0,
    "status": "ok",
    "isolated": false,
    "tool_search_off": true,
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    "bytes_per_tool_definition": 798,
    "paired_floor": 94509,
    "context": 116440,
    "delta": 21931,
    "per_tool": 4386.2
   },
   {
    "arm": "loaded_isolated",
    "n": 50,
    "round": 0,
    "status": "ok",
    "isolated": true,
    "tool_search_off": true,
    "tools_served_by_server": 50,
    "bytes_per_tool_definition": 798,
    "paired_floor": 37874,
    "context": 70480,
    "delta": 32606,
    "per_tool": 652.12
   },
   {
    "arm": "loaded_unisolated",
    "n": 50,
    "round": 0,
    "status": "ok",
    "isolated": false,
    "tool_search_off": true,
    "tools_served_by_server": 50,
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    "paired_floor": 94509,
    "context": 145780,
    "delta": 51271,
    "per_tool": 1025.42
   },
   {
    "arm": "loaded_isolated",
    "n": 200,
    "round": 0,
    "status": "ok",
    "isolated": true,
    "tool_search_off": true,
    "tools_served_by_server": 200,
    "bytes_per_tool_definition": 798,
    "paired_floor": 37874,
    "context": 168280,
    "delta": 130406,
    "per_tool": 652.03
   },
   {
    "arm": "loaded_unisolated",
    "n": 200,
    "round": 0,
    "status": "ok",
    "isolated": false,
    "tool_search_off": true,
    "tools_served_by_server": 200,
    "bytes_per_tool_definition": 798,
    "paired_floor": 94509,
    "context": 243580,
    "delta": 149071,
    "per_tool": 745.36
   },
   {
    "arm": "floor_isolated",
    "n": 0,
    "round": 1,
    "status": "ok",
    "isolated": true,
    "tool_search_off": true,
    "context": 37874,
    "delta": 0
   },
   {
    "arm": "floor_isolated",
    "n": 0,
    "round": 2,
    "status": "ok",
    "isolated": true,
    "tool_search_off": true,
    "context": 37874,
    "delta": 0
   },
   {
    "arm": "floor_unisolated",
    "n": 0,
    "round": 2,
    "status": "ok",
    "isolated": false,
    "tool_search_off": true,
    "context": 99780,
    "delta": 0
   },
   {
    "arm": "loaded_isolated",
    "n": 5,
    "round": 2,
    "status": "ok",
    "isolated": true,
    "tool_search_off": true,
    "tools_served_by_server": 5,
    "bytes_per_tool_definition": 798,
    "paired_floor": 37874,
    "context": 41140,
    "delta": 3266,
    "per_tool": 653.2
   },
   {
    "arm": "loaded_unisolated",
    "n": 5,
    "round": 2,
    "status": "ok",
    "isolated": false,
    "tool_search_off": true,
    "tools_served_by_server": 5,
    "bytes_per_tool_definition": 798,
    "paired_floor": 99780,
    "context": 116440,
    "delta": 16660,
    "per_tool": 3332.0
   },
   {
    "arm": "loaded_isolated",
    "n": 50,
    "round": 2,
    "status": "ok",
    "isolated": true,
    "tool_search_off": true,
    "tools_served_by_server": 50,
    "bytes_per_tool_definition": 798,
    "paired_floor": 37874,
    "context": 70480,
    "delta": 32606,
    "per_tool": 652.12
   },
   {
    "arm": "loaded_unisolated",
    "n": 50,
    "round": 2,
    "status": "ok",
    "isolated": false,
    "tool_search_off": true,
    "tools_served_by_server": 50,
    "bytes_per_tool_definition": 798,
    "paired_floor": 99780,
    "context": 145780,
    "delta": 46000,
    "per_tool": 920.0
   },
   {
    "arm": "loaded_isolated",
    "n": 200,
    "round": 2,
    "status": "ok",
    "isolated": true,
    "tool_search_off": true,
    "tools_served_by_server": 200,
    "bytes_per_tool_definition": 798,
    "paired_floor": 37874,
    "context": 168280,
    "delta": 130406,
    "per_tool": 652.03
   },
   {
    "arm": "loaded_unisolated",
    "n": 200,
    "round": 2,
    "status": "ok",
    "isolated": false,
    "tool_search_off": true,
    "tools_served_by_server": 200,
    "bytes_per_tool_definition": 798,
    "paired_floor": 99780,
    "context": 243580,
    "delta": 143800,
    "per_tool": 719.0
   }
  ]
 }
}