diff --git a/edgebench/tasks/arc_compiler_runtime/NOTES.md b/edgebench/tasks/arc_compiler_runtime/NOTES.md
index 86a65028..d8ca4c06 100644
--- a/edgebench/tasks/arc_compiler_runtime/NOTES.md
+++ b/edgebench/tasks/arc_compiler_runtime/NOTES.md
@@ -20,7 +20,7 @@ and runs each with `tsx` under `timeout 90`. Raw score = `100 × WEIGHTED_PASSED
   snapshot; all 361 packages that step adds are checked against v1's versions. Base: `bases/python`.
 - `judge/eval_hidden.py` is v1's inline eval program, verbatim; `judge/run.sh` and
   `judge/write_result.py` are new and write `result.json` with v1's structured-result logic.
-- `instruction.md`: v1's prompt, verbatim.
+- `instruction.md`: v1's prompt, verbatim in 1.0.0; 1.0.1 adds the `analyze()` return shape.
 
 ## Deviations from v1
 
@@ -48,6 +48,15 @@ each. The grader is deterministic. Raw score (= 0..100).
 
 Every row matches exactly, including raw and weighted counts, and equals the historical v1 scores.
 
+## Changes
+
+### 1.0.1
+
+The hidden type-system suites (1000 of the 2970 weighted points, 33.67 of 100) call `.filter` on the
+return value of `analyze()`, but nothing the agent sees gives that shape, and the starter returns an
+object. A submission that keeps the object scores 0 on those suites. `instruction.md` now states the
+shape. The judge and work images are unchanged (same tags), so grading is unchanged.
+
 ## Known issues
 
 Kept as in v1, so scores stay comparable. Fixing any of them changes scores and bumps `version`.
diff --git a/edgebench/tasks/arc_compiler_runtime/instruction.md b/edgebench/tasks/arc_compiler_runtime/instruction.md
index 33a95db0..5917ca54 100644
--- a/edgebench/tasks/arc_compiler_runtime/instruction.md
+++ b/edgebench/tasks/arc_compiler_runtime/instruction.md
@@ -1 +1,3 @@
-Implement the missing Arc compiler and runtime modules under compiler/src/. Use CHEATSHEET.md, TASK.md, and the public smoke tests as the language contract. Modify only files under compiler/src/. Do not modify tests, scoring scripts, task metadata, Dockerfiles, package files, node_modules, generated dist artifacts, source maps, or evaluator-owned files. Work offline and do not depend on hidden tests or hard-coded answers.
\ No newline at end of file
+Implement the missing Arc compiler and runtime modules under compiler/src/. Use CHEATSHEET.md, TASK.md, and the public smoke tests as the language contract. Modify only files under compiler/src/. Do not modify tests, scoring scripts, task metadata, Dockerfiles, package files, node_modules, generated dist artifacts, source maps, or evaluator-owned files. Work offline and do not depend on hidden tests or hard-coded answers.
+
+The evaluator calls `analyze(parse(lex(source)))`. `analyze` in `compiler/src/semantic.js` must return an array of diagnostics (empty when there are none), each an object with `level` (`"error"` or `"warning"`) and `message` (a string). The starter's `analyze` returns a different shape.
\ No newline at end of file
diff --git a/edgebench/tasks/arc_compiler_runtime/task.toml b/edgebench/tasks/arc_compiler_runtime/task.toml
index af688a74..8adae239 100644
--- a/edgebench/tasks/arc_compiler_runtime/task.toml
+++ b/edgebench/tasks/arc_compiler_runtime/task.toml
@@ -4,7 +4,7 @@ name = "Arc Compiler Runtime"
 category = "Systems & Software Engineering"
 language = "Python"        # v1 tasks.jsonl value (base image); the submission itself is JavaScript run by Node 20
 description = "Implement a complete TypeScript compiler pipeline (lexer, parser, type checker, code generator) for a novel programming language defined by specification documents."
-version = "1.0.0"
+version = "1.0.1"
 status = "migrated"
 
 [environment]