diff --git a/src/scoring/model.ts b/src/scoring/model.ts
index 1ec4675e75..35f930064b 100644
--- a/src/scoring/model.ts
+++ b/src/scoring/model.ts
@@ -140,12 +140,16 @@ export async function getOrCreateScoringModelSnapshot(env: Env): Promise<Scoring
 export function parsePythonNumberConstants(source: string, options: { knownOnly?: boolean } = { knownOnly: true }): Record<string, number> {
   const constants: Record<string, number> = {};
   for (const line of source.split("\n")) {
-    const match = line.match(/^([A-Z][A-Z0-9_]+)\s*=\s*([-+]?\d+(?:\.\d+)?)/);
+    // Match Python numeric literals including underscore separators (1_000_000), floats, and exponents
+    // (1e-9, 5.8e1). The previous /[-+]?\d+(?:\.\d+)?/ stopped at `_`/`e`, truncating 1_000_000 -> 1 and
+    // 1e-9 -> 1, which silently misparsed any such upstream constant and polluted the unmodeled list (#810).
+    const match = line.match(/^([A-Z][A-Z0-9_]+)\s*=\s*([-+]?(?:\d[\d_]*\.?\d*|\.\d+)(?:[eE][-+]?\d+)?)/);
     if (!match) continue;
     const name = match[1]!;
     const raw = match[2]!;
     if (options.knownOnly !== false && !SCORING_CONSTANT_NAMES.has(name)) continue;
-    constants[name] = Number(raw);
+    // Number() rejects underscore separators, so strip them before parsing.
+    constants[name] = Number(raw.replace(/_/g, ""));
   }
   return constants;
 }
diff --git a/test/unit/scoring.test.ts b/test/unit/scoring.test.ts
index 0ab930517c..2502255382 100644
--- a/test/unit/scoring.test.ts
+++ b/test/unit/scoring.test.ts
@@ -72,6 +72,20 @@ IGNORED = "not numeric"
     expect(detectActiveModel({})).toBe("unknown");
   });
 
+  it("parses underscore separators, floats, and scientific notation without truncating (#810)", () => {
+    const parsed = parsePythonNumberConstants(`
+CONTRIBUTION_SCORE_FOR_FULL_BONUS = 1_500_000
+SRC_TOK_SATURATION_SCALE = 5.8e1
+MERGED_PR_BASE_SCORE = 1e-9
+OSS_EMISSION_SHARE = 0.90
+`);
+    // The previous /[-+]?\\d+(?:\\.\\d+)?/ regex stopped at `_`/`e`: 1_500_000 -> 1, 5.8e1 -> 5.8, 1e-9 -> 1.
+    expect(parsed.CONTRIBUTION_SCORE_FOR_FULL_BONUS).toBe(1500000);
+    expect(parsed.SRC_TOK_SATURATION_SCALE).toBe(58);
+    expect(parsed.MERGED_PR_BASE_SCORE).toBe(1e-9);
+    expect(parsed.OSS_EMISSION_SHARE).toBe(0.9);
+  });
+
   it("prefers exponential saturation when mixed upstream constants are present", () => {
     const parsed = parsePythonNumberConstants(`
 MERGED_PR_BASE_SCORE = 25