diff --git a/lib/graph/prompt-builder.js b/lib/graph/prompt-builder.js
index dc11a9a..ebd2338 100644
--- a/lib/graph/prompt-builder.js
+++ b/lib/graph/prompt-builder.js
@@ -134,6 +134,14 @@ The JSON object must contain exactly these top-level fields:
 31. If the answer explicitly states a hard constraint, state that directly in userSupportedMeaning.
 32. Populate resolutionGuidance when the user's meaning genuinely implies must_remain_unresolved, may_resolve, or must_resolve. Keep it null only when no existing resolution state actually applies.
 
+## Decision Sufficiency Rule
+
+An unresolved decision between options should not remain open merely because some uncertainty still exists.
+
+Keep a decision context unresolved only when you can identify a specific unresolved factor that could materially change which option is preferred.
+
+If the currently supported evidence is sufficient to distinguish the options and no such material unresolved factor remains, resolve the existing decision context and do not ask a generic continuation question.
+
 ## Decision Option Structure Rules
 When the user presents mutually exclusive candidate actions for one unresolved choice:
 
diff --git a/tests/graph/prompt-builder.test.js b/tests/graph/prompt-builder.test.js
index e22d4c8..c73abe0 100644
--- a/tests/graph/prompt-builder.test.js
+++ b/tests/graph/prompt-builder.test.js
@@ -764,3 +764,102 @@ describe("60A.3 decision option prompt rules", () => {
     expect(altLine).toBeDefined();
   });
 });
+
+// ── Experiment 60B.4 — Decision Materiality Rule ──────────────
+
+describe("60B.4 decision materiality rule", () => {
+  const prompt = buildGraphUpdatePrompt(makeContext());
+
+  it("rule: unresolved decision not kept open merely because uncertainty remains", () => {
+    expect(prompt).toContain(
+      "should not remain open merely because some uncertainty still exists",
+    );
+  });
+
+  it("rule: continuation requires a specific unresolved factor", () => {
+    expect(prompt).toContain("specific unresolved factor");
+  });
+
+  it("rule: that factor must be capable of materially changing the preferred option", () => {
+    expect(prompt).toContain(
+      "could materially change which option is preferred",
+    );
+  });
+
+  it("rule: if no material factor remains, resolve existing decision context rather than asking generic question", () => {
+    expect(prompt).toContain(
+      "resolve the existing decision context",
+    );
+    expect(prompt).toContain(
+      "do not ask a generic continuation question",
+    );
+  });
+
+  it("does NOT introduce financial thresholds", () => {
+    expect(prompt).not.toContain("threshold");
+    expect(prompt).not.toContain("£600k");
+    expect(prompt).not.toContain("£2m");
+    expect(prompt).not.toContain("payback");
+  });
+
+  it("does NOT introduce relocation-specific examples", () => {
+    expect(prompt).not.toContain("relocation");
+    expect(prompt).not.toContain("Manchester");
+    expect(prompt).not.toContain("London");
+    expect(prompt).not.toContain("engineer");
+  });
+
+  it("does NOT introduce automatic resolution whenever one option appears better", () => {
+    // The rule must not say "always resolve" or "resolve when one looks better"
+    const sufficiencySection = prompt.split(
+      "## Decision Sufficiency Rule",
+    )[1].split("## Decision Option Structure Rules")[0];
+    expect(sufficiencySection).not.toContain("always resolve");
+    expect(sufficiencySection).not.toContain(
+      "resolve when one option",
+    );
+    expect(sufficiencySection).not.toContain("looks better");
+  });
+
+  it("does NOT introduce new schema fields or node kinds", () => {
+    // The rule text must not reference schema fields or node kinds outside the contract
+    expect(prompt).not.toContain("materiality_score");
+    expect(prompt).not.toContain("decision_sufficiency");
+    expect(prompt).not.toContain('kind "decision"');
+  });
+
+  it("does NOT mention specific currency or amounts", () => {
+    expect(prompt).not.toContain("£2 million");
+    expect(prompt).not.toContain("£600k");
+    expect(prompt).not.toContain("$1M");
+    expect(prompt).not.toContain("financial threshold");
+  });
+
+  it("existing Rule 20 preserved", () => {
+    expect(prompt).toContain(
+      "Return selectedQuestion as null only when no consequential unresolved unknown remains.",
+    );
+  });
+
+  it("is domain-general — no provider-specific, taxonomic, or keyword-based language", () => {
+    expect(prompt).not.toContain("qwen");
+    expect(prompt).not.toContain("claude");
+    expect(prompt).not.toContain("gpt");
+    expect(prompt).not.toContain("keyword");
+    expect(prompt).not.toContain("synonym");
+  });
+
+  it("preserves the possibility of keeping a decision open when grounded factor exists", () => {
+    // The rule must allow continuation when a specific unresolved factor could change the outcome
+    expect(prompt).toContain("specific unresolved factor");
+    expect(prompt).toContain("could materially change which option is preferred");
+  });
+
+  it("distinguishes uncertainty from decision-relevant uncertainty", () => {
+    // The rule must distinguish mere uncertainty from uncertainty that matters to the decision
+    const sufficiencySection = prompt.split(
+      "## Decision Sufficiency Rule",
+    )[1].split("## Decision Option Structure Rules")[0];
+    expect(sufficiencySection).toContain("should not remain open merely because some uncertainty still exists");
+  });
+});