diff --git a/src/scoring/preview.ts b/src/scoring/preview.ts
index 03eafc9341..d2a585c5eb 100644
--- a/src/scoring/preview.ts
+++ b/src/scoring/preview.ts
@@ -169,7 +169,12 @@ export type ScorePreviewResult = {
     issueDiscoveryShare: number;
   };
   scoreEstimate: {
+    /** Computed base score (the earned foundation before multipliers apply). */
     baseScore: number;
+    /** The maximum possible baseScore given the active model and snapshot constants; used by the score
+     *  breakdown to surface saturation vs sub-cap status. Undefined when a fixedBaseScore override is in
+     *  effect (the override is not bounded by the model cap). */
+    baseScoreCap?: number;
     densityMultiplier: number;
     contributionBonus: number;
     labelMultiplier: number;
@@ -362,6 +367,12 @@ function computeScoreCore(
       : snapshot.activeModel === "pending_saturation_model"
         ? saturationBaseScore
         : densityBaseScore;
+  const baseScoreCap =
+    fixedBaseScore !== undefined
+      ? undefined
+      : snapshot.activeModel === "pending_saturation_model"
+        ? constant(constants, "MERGED_PR_BASE_SCORE") + constant(constants, "MAX_CONTRIBUTION_BONUS")
+        : constant(constants, "MERGED_PR_BASE_SCORE") * constant(constants, "MAX_CODE_DENSITY_MULTIPLIER") + constant(constants, "MAX_CONTRIBUTION_BONUS");
   const activeContributionBonus = snapshot.activeModel === "pending_saturation_model" ? saturationContributionBonusValue : densityContributionBonus;
   const labelMultiplier = selectLabelMultiplier(input.labels ?? [], config?.labelMultipliers ?? {}, config?.defaultLabelMultiplier ?? 1);
   const branchEligibility = normalizeBranchEligibility(input);
@@ -443,6 +454,7 @@ function computeScoreCore(
     },
     scoreEstimate: {
       baseScore: roundScore(baseScore),
+      ...(baseScoreCap !== undefined ? { baseScoreCap: roundScore(baseScoreCap) } : {}),
       densityMultiplier: roundScore(densityMultiplier),
       contributionBonus: roundScore(activeContributionBonus),
       labelMultiplier,
diff --git a/src/services/score-breakdown.ts b/src/services/score-breakdown.ts
index 69e2a7f95f..e3e96255a9 100644
--- a/src/services/score-breakdown.ts
+++ b/src/services/score-breakdown.ts
@@ -31,6 +31,48 @@ function bandForMultiplier(value: number, blockedAtZero = true): ScoreMultiplier
   return "reduced";
 }
 
+// Sibling of densityBreakdown for the saturated base-score value (#808 / entrius/gittensor
+// constants.py): `base_score = MERGED_PR_BASE_SCORE × (1 - exp(-src_tok / SRC_TOK_SATURATION_SCALE))
+// + min(total_token_score / CONTRIBUTION_SCORE_FOR_FULL_BONUS, 1) × MAX_CONTRIBUTION_BONUS`.
+// densityBreakdown surfaces the saturation ratio (densityMultiplier); this surfaces the
+// actual base_score the contributor has earned — the foundation that flows into estimatedMergedScore
+// before the multipliers apply — so a miner sees both the curve and the resulting cap contribution.
+// Uses preview.scoreEstimate.baseScoreCap (carried from the scoring core, which has the snapshot
+// constants) to compute a relative saturation ratio instead of a hardcoded threshold.
+const BASE_SCORE_SATURATION_RATIO = 0.95;
+
+function baseScoreBreakdown(preview: ScorePreviewResult): ScoreMultiplierBreakdown {
+  const { baseScore, baseScoreCap, contributionBonus } = preview.scoreEstimate;
+  const baseGatePassed = preview.gates.baseTokenGatePassed;
+  if (!baseGatePassed) {
+    return {
+      component: "baseScore",
+      band: "blocked",
+      summary: `Base score is not yet in the score pipeline — the change does not meet the minimum meaningful source-change threshold (current base is ${roundBand(baseScore)}).`,
+      lever: "Add more substantive source changes or tighten the diff before relying on this preview.",
+      leverageScore: 75,
+    };
+  }
+  const saturated = baseScoreCap !== undefined && baseScoreCap > 0 && baseScore / baseScoreCap >= BASE_SCORE_SATURATION_RATIO;
+  const hasBonus = contributionBonus > 0;
+  const bonusClause = hasBonus ? `; contribution bonus contributing at ${roundBand(contributionBonus)}` : "; contribution bonus not contributing";
+  const capClause = baseScoreCap === undefined
+    ? "using a fixed base score override (not bounded by the model cap)"
+    : saturated
+      ? "saturated near the score cap"
+      : "contributing toward the score cap";
+  const summary = `Base score is ${capClause} (current base ${roundBand(baseScore)}${bonusClause}).`;
+  return {
+    component: "baseScore",
+    band: saturated ? "full" : "neutral",
+    summary,
+    lever: saturated
+      ? "Maintain source quality on subsequent contributions; the base-score pipeline is at saturation."
+      : "Keep source changes substantive and proportional to supporting changes for the contribution bonus to continue earning.",
+    leverageScore: saturated ? 3 : hasBonus ? 7 : 12,
+  };
+}
+
 function densityBreakdown(preview: ScorePreviewResult): ScoreMultiplierBreakdown {
   const { densityMultiplier, contributionBonus } = preview.scoreEstimate;
   const baseGatePassed = preview.gates.baseTokenGatePassed;
@@ -308,6 +350,7 @@ function pickHighestLeverage(components: ScoreMultiplierBreakdown[]): ScoreBreak
  */
 export function explainScoreBreakdown(preview: ScorePreviewResult): ScoreBreakdownExplanation {
   const components = [
+    baseScoreBreakdown(preview),
     densityBreakdown(preview),
     contributionBonusBreakdown(preview),
     labelMultiplierBreakdown(preview),
diff --git a/test/unit/score-breakdown.test.ts b/test/unit/score-breakdown.test.ts
index 4a6038612d..b8fd118729 100644
--- a/test/unit/score-breakdown.test.ts
+++ b/test/unit/score-breakdown.test.ts
@@ -16,7 +16,7 @@ const snapshot: ScoringModelSnapshotRecord = {
     MERGED_PR_BASE_SCORE: 25,
     MIN_TOKEN_SCORE_FOR_BASE_SCORE: 5,
     MAX_CODE_DENSITY_MULTIPLIER: 1.15,
-    MAX_CONTRIBUTION_BONUS: 25,
+    MAX_CONTRIBUTION_BONUS: 5,
     CONTRIBUTION_SCORE_FOR_FULL_BONUS: 1500,
     STANDARD_ISSUE_MULTIPLIER: 1.33,
     MAINTAINER_ISSUE_MULTIPLIER: 1.66,
@@ -75,6 +75,7 @@ describe("explainScoreBreakdown", () => {
     const componentNames = breakdown.components.map((entry) => entry.component);
     expect(componentNames).toEqual(
       expect.arrayContaining([
+        "baseScore",
         "densityMultiplier",
         "contributionBonus",
         "labelMultiplier",
@@ -380,7 +381,9 @@ describe("explainScoreBreakdown", () => {
     const breakdown = explainScoreBreakdown(preview);
     expect(breakdown.components.find((entry) => entry.component === "densityMultiplier")).toMatchObject({ band: "blocked" });
     expect(breakdown.components.find((entry) => entry.component === "issueMultiplier")?.lever).toMatch(/Fix linked issue state/i);
-    expect(breakdown.highestLeverageLever.component).toBe("densityMultiplier");
+    // baseScore and densityMultiplier tie at leverageScore 75 when the gate is not passed;
+    // baseScore wins alphabetically as the root-cause lever.
+    expect(breakdown.highestLeverageLever.component).toBe("baseScore");
   });
 
   it("selects a reduced multiplier as highest leverage when nothing is fully blocked", () => {
@@ -446,4 +449,204 @@ describe("explainScoreBreakdown", () => {
     expect(breakdown.components.find((entry) => entry.component === "credibilityMultiplier")).toMatchObject({ band: "blocked" });
     expect(breakdown.components.find((entry) => entry.component === "openPrMultiplier")).toMatchObject({ band: "blocked" });
   });
+
+  it("blocks base-score projection when the source-token gate has not passed", () => {
+    const preview = buildScorePreview({
+      repo,
+      snapshot,
+      input: {
+        repoFullName: repo.fullName,
+        contributorLogin: "miner",
+        sourceTokenScore: 0,
+        totalTokenScore: 0,
+        sourceLines: 4,
+        openPrCount: 0,
+        credibility: 1,
+      },
+    });
+    const entry = explainScoreBreakdown(preview).components.find((c) => c.component === "baseScore")!;
+    expect(entry).toMatchObject({ band: "blocked", leverageScore: 75 });
+    expect(entry.summary).toMatch(/not yet in the score pipeline|minimum meaningful source-change/);
+  });
+
+  it("surfaces a neutral (sub-cap) base score with the contribution bonus present", () => {
+    const preview = buildScorePreview({
+      repo,
+      snapshot,
+      input: {
+        repoFullName: repo.fullName,
+        contributorLogin: "miner",
+        sourceTokenScore: 25,
+        totalTokenScore: 800,
+        sourceLines: 120,
+        openPrCount: 0,
+        credibility: 1,
+      },
+    });
+    const entry = explainScoreBreakdown(preview).components.find((c) => c.component === "baseScore")!;
+    expect(entry).toMatchObject({ band: "neutral" });
+    expect(entry.summary).toMatch(/contributing toward|base \d|contribution bonus/);
+  });
+
+  it("surfaces a neutral base-score branch when gate passed but no contribution bonus earned", () => {
+    const preview = buildScorePreview({
+      repo,
+      snapshot,
+      input: {
+        repoFullName: repo.fullName,
+        contributorLogin: "miner",
+        sourceTokenScore: 10,
+        totalTokenScore: 0,
+        sourceLines: 40,
+        openPrCount: 0,
+        credibility: 1,
+      },
+    });
+    const entry = explainScoreBreakdown(preview).components.find((c) => c.component === "baseScore")!;
+    expect(entry).toMatchObject({ band: "neutral" });
+    expect(entry.leverageScore).toBe(12);
+    expect(entry.summary).toMatch(/contributing toward|base \d|contribution bonus not contributing/);
+  });
+
+  it("surfaces the base score as saturated (full) near the score cap", () => {
+    // Density model: baseScoreCap = MERGED_PR_BASE_SCORE × MAX_CODE_DENSITY_MULTIPLIER +
+    // MAX_CONTRIBUTION_BONUS = 25 × 1.15 + 5 = 33.75. Need baseScore / baseScoreCap ≥ 0.95 (≈ 32.06).
+    // With densityMultiplier = 1.15 and totalTokenScore = 1500 (full bonus 5), baseScore = 28.75 + 5 = 33.75.
+    const preview = buildScorePreview({
+      repo,
+      snapshot,
+      input: {
+        repoFullName: repo.fullName,
+        contributorLogin: "miner",
+        sourceTokenScore: 200,
+        totalTokenScore: 1500,
+        sourceLines: 170,
+        openPrCount: 0,
+        credibility: 1,
+      },
+    });
+    const entry = explainScoreBreakdown(preview).components.find((c) => c.component === "baseScore")!;
+    expect(entry).toMatchObject({ band: "full" });
+    expect(entry.summary).toMatch(/saturated near the score cap/);
+    expect(JSON.stringify(explainScoreBreakdown(preview))).not.toMatch(FORBIDDEN);
+  });
+
+  it("adapts the saturation threshold to non-default snapshot constants (regression)", () => {
+    // Use a snapshot with different constants to prove the threshold is not hardcoded to 29.5.
+    // If MERGED_PR_BASE_SCORE=50 and MAX_CONTRIBUTION_BONUS=10, cap = 50 × 1.15 + 10 = 67.5.
+    // 95% saturation ≈ 64.13. Inputs that would give baseScore=32 (well below 64) must NOT read as full.
+    // Cap: 50 × 1.15 + 10 = 67.5. 95% saturation ≈ 64.13.
+    const altSnapshot: ScoringModelSnapshotRecord = {
+      ...snapshot,
+      id: "score-model-alt-cap",
+      constants: {
+        ...snapshot.constants,
+        MERGED_PR_BASE_SCORE: 50,
+        MAX_CONTRIBUTION_BONUS: 10,
+      },
+    };
+    // With source 200 / lines 170 → density 1.15 → baseDensity = 50 × 1.15 = 57.5.
+    // totalTokenScore 0 → contributionBonus 0 → baseScore = 57.5 < 64.13 → NOT saturated.
+    const subCap = buildScorePreview({
+      repo,
+      snapshot: altSnapshot,
+      input: {
+        repoFullName: repo.fullName,
+        contributorLogin: "miner",
+        sourceTokenScore: 200,
+        totalTokenScore: 0,
+        sourceLines: 170,
+        openPrCount: 0,
+        credibility: 1,
+      },
+    });
+    const notSaturated = explainScoreBreakdown(subCap).components.find((c) => c.component === "baseScore")!;
+    expect(notSaturated).toMatchObject({ band: "neutral" });
+    // Full bonus (totalTokenScore >= 1500) → baseScore = 57.5 + 10 = 67.5, which IS ≥ 95% of 67.5.
+    const saturated = buildScorePreview({
+      repo,
+      snapshot: altSnapshot,
+      input: {
+        repoFullName: repo.fullName,
+        contributorLogin: "miner",
+        sourceTokenScore: 200,
+        totalTokenScore: 1500,
+        sourceLines: 170,
+        openPrCount: 0,
+        credibility: 1,
+      },
+    });
+    const isSaturated = explainScoreBreakdown(saturated).components.find((c) => c.component === "baseScore")!;
+    expect(isSaturated).toMatchObject({ band: "full" });
+    expect(isSaturated.summary).toMatch(/saturated near the score cap/);
+    expect(JSON.stringify(explainScoreBreakdown(saturated))).not.toMatch(FORBIDDEN);
+  });
+
+  it("handles fixedBaseScore override (baseScoreCap undefined, copy without cap mention)", () => {
+    // When fixedBaseScore is set, the cap is undefined — the copy should not mention "score cap".
+    // Use sourceTokenScore >= MIN_TOKEN_SCORE_FOR_BASE_SCORE (5) so the gate passes.
+    const preview = buildScorePreview({
+      repo,
+      snapshot,
+      input: {
+        repoFullName: repo.fullName,
+        contributorLogin: "miner",
+        sourceTokenScore: 10,
+        totalTokenScore: 0,
+        sourceLines: 40,
+        openPrCount: 0,
+        credibility: 1,
+        fixedBaseScore: 50,
+      },
+    });
+    const entry = explainScoreBreakdown(preview).components.find((c) => c.component === "baseScore")!;
+    expect(entry).toMatchObject({ band: "neutral" });
+    expect(entry.summary).toMatch(/fixed base score override/);
+    expect(entry.summary).not.toMatch(/score cap/);
+    expect(JSON.stringify(explainScoreBreakdown(preview))).not.toMatch(FORBIDDEN);
+  });
+
+  it("derives the base-score cap from the saturation model constants", () => {
+    // Saturation model: baseScoreCap = MERGED_PR_BASE_SCORE + MAX_CONTRIBUTION_BONUS = 25 + 5 = 30.
+    // Need baseScore / 30 >= 0.95 (≈ 28.5). With source 200 / scale 58: 25 × (1 - exp(-200/58)) ≈ 24.2,
+    // plus full bonus 5 → baseScore = 29.2. Slightly below 28.5 → NOT saturated.
+    // Use a higher src to push past 95%: with source 400: 25 × (1 - exp(-400/58)) ≈ 24.99 + 5 = 29.99 ≥ 28.5.
+    const satSnapshot: ScoringModelSnapshotRecord = {
+      ...snapshot,
+      id: "score-model-saturation",
+      activeModel: "pending_saturation_model",
+    };
+    const subCap = buildScorePreview({
+      repo,
+      snapshot: satSnapshot,
+      input: {
+        repoFullName: repo.fullName,
+        contributorLogin: "miner",
+        sourceTokenScore: 100,
+        totalTokenScore: 0,
+        sourceLines: 100,
+        openPrCount: 0,
+        credibility: 1,
+      },
+    });
+    const notSaturated = explainScoreBreakdown(subCap).components.find((c) => c.component === "baseScore")!;
+    expect(notSaturated).toMatchObject({ band: "neutral" });
+    const saturated = buildScorePreview({
+      repo,
+      snapshot: satSnapshot,
+      input: {
+        repoFullName: repo.fullName,
+        contributorLogin: "miner",
+        sourceTokenScore: 400,
+        totalTokenScore: 1500,
+        sourceLines: 400,
+        openPrCount: 0,
+        credibility: 1,
+      },
+    });
+    const isSaturated = explainScoreBreakdown(saturated).components.find((c) => c.component === "baseScore")!;
+    expect(isSaturated).toMatchObject({ band: "full" });
+    expect(isSaturated.summary).toMatch(/saturated near the score cap/);
+    expect(JSON.stringify(explainScoreBreakdown(saturated))).not.toMatch(FORBIDDEN);
+  });
 });